CA2268597C - Process for hydraulically fracturing oil and gas wells utilizing coiled tubing - Google Patents
Process for hydraulically fracturing oil and gas wells utilizing coiled tubing Download PDFInfo
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- CA2268597C CA2268597C CA002268597A CA2268597A CA2268597C CA 2268597 C CA2268597 C CA 2268597C CA 002268597 A CA002268597 A CA 002268597A CA 2268597 A CA2268597 A CA 2268597A CA 2268597 C CA2268597 C CA 2268597C
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- coiled tubing
- pay zone
- pay
- tubing string
- fracturing
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Classifications
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
- E21B17/20—Flexible or articulated drilling pipes, e.g. flexible or articulated rods, pipes or cables
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B19/00—Handling rods, casings, tubes or the like outside the borehole, e.g. in the derrick; Apparatus for feeding the rods or cables
- E21B19/22—Handling reeled pipe or rod units, e.g. flexible drilling pipes
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
Abstract
A wellbore (10) in an earth formation (12) having a casing (14) and a plurality of pay or production zones (32, 34, 36) provided in the formation. A coiled tubing string (18) from a reel (20) is injected by an injector (24) into the wellbore (10) for first perforating casing section (38) at each pay zone (32, 34, 36) in a single pass of the coiled tubing (18). Next, the coiled tubing (18) is utilized for hydraulic fracturing each of the pay zones (32, 34, 36) individually from the lowermost pay zone (32) to the uppermost pay zone (36) in a single pass of the coiled tubing (18). Each pay zone (32, 34, 36) is isolated for the hydraulic fracturing. An upper packer (44 or 54) is provided above each of the pay zones for isolation and a lower packer (56) or sand plug (50) is utilized for isolating the lower or outermost end of each pay zone (32, 34, 36). Swab cups (58, 54A, 56A, 54B, 56B) are also utilized for isolation of pay zones.
Description
PROCESS FOR HYDRAULICALLY FRACTURING OIL AND GAS WELLS
UTILIZING COILED TUBING
Field of the Invention This invention relates to a process for hydraulically fracturing oil and gas wells utilizing coiled tubing, and particularly to such a process in which the oil and gas wells have multiple production or pay zones.
BACKGROUND OF THE INVENTION
Hydraulic fracturing is a term that has been applied to a variety of methods used to stimulate the production of fluids such as oil, natural gas, brines, etc., from subterranean formations. In hydraulic fracturing, a fracturing fluid is injected through a wellbore and against the face of the formation at a pressure and flow rate at least sufficient to overcome the minimum principal stress in the reservoir and extend a fractures) into the formation.
The fracturing fluid usually carries a proppant such as 20-40 mesh sand, bauxite, glass beads, etc., suspended in the fracturing fluid and transported into a fracture. The proppant then keeps the formation from closing back down upon itself when the pressure is released. The proppant filled fractures provide permeable channels through which the formation fluids can flow to the wellbore and thereafter be withdrawn.
Hydraulic fracturing has been used for many years as a stimulation technique and extensive work has been done to some problems present at each stage of the process. For example, a fracturing fluid is often exposed to high temperatures and/or high pump rates and shear which can cause the fluids to degrade and to prematurely "drop" the proppant before the fracturing operation is completed.
Considerable effort has, therefore, been spent trying to design fluids that will satisfactorily meet these rigorous conditions.
High permeability formations such as those having permeabilities in excess of 50 millidarcy and particularly in excess of 200 millidarcy, present special challenges, especially when the reservoir temperature is above about 400°F. In these situations, the amount of fluid lost to the formation can be very high, resulting in increased damage and decreased fracture length. Further, the difference in permeability between the formation and the fracture is less than that realized in less permeable formations. Improved fracture cleanup is therefore necessary in order to maximize well productivity.
A wide variety of fluids has been developed, but most of the fracturing fluids used today are aqueous based liquids which have been engineered for use in low permeability formations and are generally not well suited for use in higher permeability formations.
It has been common heretofore for the hydraulic fracturing of old oil and gas wells to utilize a workover rig and wireline for setting a packer and bridge plug combination about jointed tubing for isolation of each production zone for hydraulic fracturing. Such a fracturing operation is time consuming. For example, in a gas well with four production zones, the completions involving a fracturing and workover program may take about ten to fifteen days. If hydraulic fracturing is provided individually with a workover rig for each production zone in a multiple zone well, multiple trips to the well for perforating and multiple trips to the well for hydraulic fracturing are required. Obviously, substantial time and expense are involved with such a process utilizing a workover rig or other isolation methods.
However, prior art processes have been utilized heretofore in which coiled tubing without a workover rig has been used for fracturing a gas reservoir. Upper and lower mechanical packers were utilized on upper and lower sides of the production zones. The setting and release of the mechanical packers were required for each pay zone. For example, U.S. Patent No. 5,427,177 dated June 27, 1995 shows the utilization of coiled tubing particularly for the completion of lateral wells and multilateral wells. A re-entry tool on coiled tubing has a plurality of inflatable casing packers thereon to block the annulus and permit various operations such as fracturing or acidizing.
It is an object of this invention to provide a process for hydraulically fracturing oil and gas wells having multiple pay zones utilizing a coiled tubing string and fracturing the desired pay zones in a single pass of the coiled tubing string.
Another object of the invention is to provide such a process in which the multiple pay zones are perforated prior to the hydraulic fracturing of the pay zones.
A further object of the invention is to provide such a process for fracturing a multizone well with coiled tubing in which a fracturing fluid is utilized which has a low friction for minimizing the fluid pressure within the coiled tubing during the fracturing process.
Another object of the invention is to provide a process for fracturing a multizone well with coiled tubing in which each selected pay zone is isolated separately in a minimum of time while utilizing the associated coiled tubing string with the coiled tubing movable after fracturing to another pay zone for isolation of subsequent pay zones.
SUMMARY OF THE INVENTION
This invention is directed to a process for hydraulically fracturing of oil and gas wells having multiple pay zones utilizing coiled tubing with the multiple pay zones fractured with a single pass of the coiled tubing.
Each pay zone is individually isolated and fractured. Prior to fracturing the multiple pay zones are perforated in a single pass of a wireline or a coiled tubing string. The pay zones are isolated with a sand plug on a lower end of a pay zone or with swab cups.
For hydraulic fracturing of the multiple pay zones after the zones have been perforated, the lowermost or farthermost pay zone is initially hydraulically fractured, then the bottom hole assembly on the end of the coiled tubing is moved to the perforation at the next pay zone for hydraulic fracturing. This sequence continues until all of the very zones have been individually fractured and stimulated.
For isolation of each pay zone in one embodiment, a mechanical packer is positioned adjacent the upper side of the pay zone and after fracturing, a sand plug is deposited adjacent the lower side of the pay zone. Then, upon release of the mechanical packer, the coiled tubing string is raised to the next pay zone. For the lowermost pay zone, a bridge plug may sometimes be utilized without a sand plug, and for the uppermost pay zone, a wellhead hanger may sometimes be utilized adjacent the upper end of the pay zone for isolation without requiring a mechanical packer.
UTILIZING COILED TUBING
Field of the Invention This invention relates to a process for hydraulically fracturing oil and gas wells utilizing coiled tubing, and particularly to such a process in which the oil and gas wells have multiple production or pay zones.
BACKGROUND OF THE INVENTION
Hydraulic fracturing is a term that has been applied to a variety of methods used to stimulate the production of fluids such as oil, natural gas, brines, etc., from subterranean formations. In hydraulic fracturing, a fracturing fluid is injected through a wellbore and against the face of the formation at a pressure and flow rate at least sufficient to overcome the minimum principal stress in the reservoir and extend a fractures) into the formation.
The fracturing fluid usually carries a proppant such as 20-40 mesh sand, bauxite, glass beads, etc., suspended in the fracturing fluid and transported into a fracture. The proppant then keeps the formation from closing back down upon itself when the pressure is released. The proppant filled fractures provide permeable channels through which the formation fluids can flow to the wellbore and thereafter be withdrawn.
Hydraulic fracturing has been used for many years as a stimulation technique and extensive work has been done to some problems present at each stage of the process. For example, a fracturing fluid is often exposed to high temperatures and/or high pump rates and shear which can cause the fluids to degrade and to prematurely "drop" the proppant before the fracturing operation is completed.
Considerable effort has, therefore, been spent trying to design fluids that will satisfactorily meet these rigorous conditions.
High permeability formations such as those having permeabilities in excess of 50 millidarcy and particularly in excess of 200 millidarcy, present special challenges, especially when the reservoir temperature is above about 400°F. In these situations, the amount of fluid lost to the formation can be very high, resulting in increased damage and decreased fracture length. Further, the difference in permeability between the formation and the fracture is less than that realized in less permeable formations. Improved fracture cleanup is therefore necessary in order to maximize well productivity.
A wide variety of fluids has been developed, but most of the fracturing fluids used today are aqueous based liquids which have been engineered for use in low permeability formations and are generally not well suited for use in higher permeability formations.
It has been common heretofore for the hydraulic fracturing of old oil and gas wells to utilize a workover rig and wireline for setting a packer and bridge plug combination about jointed tubing for isolation of each production zone for hydraulic fracturing. Such a fracturing operation is time consuming. For example, in a gas well with four production zones, the completions involving a fracturing and workover program may take about ten to fifteen days. If hydraulic fracturing is provided individually with a workover rig for each production zone in a multiple zone well, multiple trips to the well for perforating and multiple trips to the well for hydraulic fracturing are required. Obviously, substantial time and expense are involved with such a process utilizing a workover rig or other isolation methods.
However, prior art processes have been utilized heretofore in which coiled tubing without a workover rig has been used for fracturing a gas reservoir. Upper and lower mechanical packers were utilized on upper and lower sides of the production zones. The setting and release of the mechanical packers were required for each pay zone. For example, U.S. Patent No. 5,427,177 dated June 27, 1995 shows the utilization of coiled tubing particularly for the completion of lateral wells and multilateral wells. A re-entry tool on coiled tubing has a plurality of inflatable casing packers thereon to block the annulus and permit various operations such as fracturing or acidizing.
It is an object of this invention to provide a process for hydraulically fracturing oil and gas wells having multiple pay zones utilizing a coiled tubing string and fracturing the desired pay zones in a single pass of the coiled tubing string.
Another object of the invention is to provide such a process in which the multiple pay zones are perforated prior to the hydraulic fracturing of the pay zones.
A further object of the invention is to provide such a process for fracturing a multizone well with coiled tubing in which a fracturing fluid is utilized which has a low friction for minimizing the fluid pressure within the coiled tubing during the fracturing process.
Another object of the invention is to provide a process for fracturing a multizone well with coiled tubing in which each selected pay zone is isolated separately in a minimum of time while utilizing the associated coiled tubing string with the coiled tubing movable after fracturing to another pay zone for isolation of subsequent pay zones.
SUMMARY OF THE INVENTION
This invention is directed to a process for hydraulically fracturing of oil and gas wells having multiple pay zones utilizing coiled tubing with the multiple pay zones fractured with a single pass of the coiled tubing.
Each pay zone is individually isolated and fractured. Prior to fracturing the multiple pay zones are perforated in a single pass of a wireline or a coiled tubing string. The pay zones are isolated with a sand plug on a lower end of a pay zone or with swab cups.
For hydraulic fracturing of the multiple pay zones after the zones have been perforated, the lowermost or farthermost pay zone is initially hydraulically fractured, then the bottom hole assembly on the end of the coiled tubing is moved to the perforation at the next pay zone for hydraulic fracturing. This sequence continues until all of the very zones have been individually fractured and stimulated.
For isolation of each pay zone in one embodiment, a mechanical packer is positioned adjacent the upper side of the pay zone and after fracturing, a sand plug is deposited adjacent the lower side of the pay zone. Then, upon release of the mechanical packer, the coiled tubing string is raised to the next pay zone. For the lowermost pay zone, a bridge plug may sometimes be utilized without a sand plug, and for the uppermost pay zone, a wellhead hanger may sometimes be utilized adjacent the upper end of the pay zone for isolation without requiring a mechanical packer.
For isolation of each pay zone in another embodiment, swab cups may be utilized at opposed sides or ends of the pay zone. In one embodiment, a downwardly facing swab cup is positioned adjacent the upper end of the pay zone and a sand plug is provided after fracturing adjacent the lower end of the pay zone. In another embodiment, a downwardly facing swab cup is positioned adjacent the upper end of each pay zone and an upwardly facing swab cup is positioned adjacent the lower end of each pay zone for isolating each pay zone prior to hydraulic fracturing. The swab cups are normally spaced from each other a distance generally equal to the maximum thickness pay zone. Then, upon movement of the coiled tubing string to an adjacent pay zone, the swab cups do not have to be adjusted unless the thicknesses of the pay zones are widely different. Swab cups do not require setting and releasing.
Thus, the swab cups and coiled tubing string can be moved quickly to subsequent pay zones. If desired, a plurality of swab cups may be provided on each side of a pay zone for isolation of the pay zone.
The fracturing material utilized with the coiled tubing of this invention provides a low friction against the coiled tubing when flowing therein to minimize the pressure in the coiled tubing which are particularly desirable at depths over about 4,500 feet. Coiled tubing normally has an external diameter of between 1 3/4 inches and 2 3/8 inches and in some instances as great as 2 7/8 inches. Friction from the fracturing material can be reduced by reducing the rate of injection or by increasing the diameter of the coiled tubing. A low injection rate is normally undesirable for placement of the proppant and for effective fracturing of the formation. Coiled tubing has operating limitations and it is necessary that fluid pressure within the coiled tubing be within the operating range of the coiled tubing.
A fracturing fluid for a specific job is selected based primarily on (1) the friction, (2) the surface pressure limitation, (3) the safe operating limits of the coiled tubing, (4) the desired fracture geometry, and (5) the characteristics of the formation. The use of a fracturing fluid having a low friction permits the utilization of a smaller diameter coiled tubing in many instances, particularly at depths over 4,500 feet. For example, at formations at about 7,000 feet in depth, a low friction fluid may be used for fracturing whereas a higher friction fluid is generally limited to substantially shallower formations.
A broad aspect of the invention provides a process in a fracturing system for fracturing wells having a pay zone in a borehole, the system utilizing coiled tubing wound on a reel and an injector for inserting a coiled tubing string from the reel within the borehole; said process comprising the following steps: lowering the coiled tubing string within the borehole to the pay zone; providing a packer about the coiled tubing inwardly of the pay zone;
injecting a fracturing material from the coiled tubing string into the perforated pay zone, wherein the fracturing material is a viscoelastic surfactant; and injecting sand from said coiled tubing string into the pay zone after injection of said fracturing material to form a sand plug covering the pay zone.
Another broad aspect of the invention provides a process in a fracturing system for fracturing gas wells and having a plurality of spaced pay zones in a borehole, the system utilizing coiled tubing apparatus including a reel and an injector for inserting a coiled tubing string from the reel within the borehole; said process comprising the following steps: perforating a plurality of pay zones from a farthermost pay zone; injecting the coiled tubing string within the borehole for lowering the coiled tubing string to an outermost perforated pay zone; providing a packer about the coiled tubing string inwardly of the outermost perforated pay zone; injecting a fracturing material from the coiled tubing string into the outermost perforated pay zone, wherein the fracturing material is a viscoelastic surfactant; and injecting sand from said coiled tubing string after injection of said fracturing material to form a sand plug covering the outermost perforated pay zone.
A further broad aspect of the invention provides a process for perforating and fracturing shallow gas wells having a plurality of spaced pay zones in a borehole comprising the steps of: perforating the spaced pay zones with a perforating apparatus from an outermost pay zone to an innermost pay zone; providing a coiled tubing reel and an injector adjacent the borehole; unreeling and injecting the coiled tubing downhole in the borehole to the outermost perforated pay zone; providing a packer about the coiled tubing inwardly of the outermost perforated pay zone;
injecting a fracturing material from the coiled tubing string into the outermost perforated pay zone, wherein the fracturing material is a viscoelastic surfactant; and injecting sand from said coiled tubing string into said outermost perforated pay zone after injection of said fracturing material to form a sand plug covering said outermost perforated pay zone.
A further broad aspect of the invention provides a process in a fracturing system for hydraulically fracturing wells having a plurality of spaced pay zones in a borehole, the system utilizing coiled tubing apparatus including a reel and an injector for inserting a coiled tubing string from the reel; said process including the steps of:
perforating said spaced pay zones with a perforating apparatus from the outermost pay zone to the innermost pay zone; providing a pair of spaced swab cups on the coiled tubing string for positioning on opposite sides of a selected perforated pay zone; inserting the coiled tubing string with the swab cups thereon within the borehole for positioning on opposed sides of said selected perforated pay zone; and injecting a fracturing material from the coiled tubing string within said selected perforated pay zone between said pair of swab cups, wherein the fracturing material is a viscoelastic surfactant.
A further broad aspect of the invention provides a process for hydraulically fracturing a pay zone in a well having a plurality of spaced pay zones in a borehole comprising the following steps: perforating the pay zones;
providing a coiled tubing string having a pair of spaced swab cups thereon for positioning on opposed sides of a selected pay zone; inserting the coiled tubing string with the pair of spaced swab cups thereon within the borehole and lowering the coiled tubing string to the selected pay zone with each one of the pair of the swab cups positioned on an opposed side of the selected pay zone; and injecting a fracturing material from the coiled tubing string within the selected pay zone between the pair of swab cups, wherein the fracturing material is a viscoelastic surfactant.
A further broad aspect of the invention provides a process for perforating and fracturing a plurality of spaced pay zones in a borehole for a well; the system utilizing coiled tubing apparatus including a reel and injector for inserting a coiled tubing string from the reel within the borehole; said process comprising the following steps:
Thus, the swab cups and coiled tubing string can be moved quickly to subsequent pay zones. If desired, a plurality of swab cups may be provided on each side of a pay zone for isolation of the pay zone.
The fracturing material utilized with the coiled tubing of this invention provides a low friction against the coiled tubing when flowing therein to minimize the pressure in the coiled tubing which are particularly desirable at depths over about 4,500 feet. Coiled tubing normally has an external diameter of between 1 3/4 inches and 2 3/8 inches and in some instances as great as 2 7/8 inches. Friction from the fracturing material can be reduced by reducing the rate of injection or by increasing the diameter of the coiled tubing. A low injection rate is normally undesirable for placement of the proppant and for effective fracturing of the formation. Coiled tubing has operating limitations and it is necessary that fluid pressure within the coiled tubing be within the operating range of the coiled tubing.
A fracturing fluid for a specific job is selected based primarily on (1) the friction, (2) the surface pressure limitation, (3) the safe operating limits of the coiled tubing, (4) the desired fracture geometry, and (5) the characteristics of the formation. The use of a fracturing fluid having a low friction permits the utilization of a smaller diameter coiled tubing in many instances, particularly at depths over 4,500 feet. For example, at formations at about 7,000 feet in depth, a low friction fluid may be used for fracturing whereas a higher friction fluid is generally limited to substantially shallower formations.
A broad aspect of the invention provides a process in a fracturing system for fracturing wells having a pay zone in a borehole, the system utilizing coiled tubing wound on a reel and an injector for inserting a coiled tubing string from the reel within the borehole; said process comprising the following steps: lowering the coiled tubing string within the borehole to the pay zone; providing a packer about the coiled tubing inwardly of the pay zone;
injecting a fracturing material from the coiled tubing string into the perforated pay zone, wherein the fracturing material is a viscoelastic surfactant; and injecting sand from said coiled tubing string into the pay zone after injection of said fracturing material to form a sand plug covering the pay zone.
Another broad aspect of the invention provides a process in a fracturing system for fracturing gas wells and having a plurality of spaced pay zones in a borehole, the system utilizing coiled tubing apparatus including a reel and an injector for inserting a coiled tubing string from the reel within the borehole; said process comprising the following steps: perforating a plurality of pay zones from a farthermost pay zone; injecting the coiled tubing string within the borehole for lowering the coiled tubing string to an outermost perforated pay zone; providing a packer about the coiled tubing string inwardly of the outermost perforated pay zone; injecting a fracturing material from the coiled tubing string into the outermost perforated pay zone, wherein the fracturing material is a viscoelastic surfactant; and injecting sand from said coiled tubing string after injection of said fracturing material to form a sand plug covering the outermost perforated pay zone.
A further broad aspect of the invention provides a process for perforating and fracturing shallow gas wells having a plurality of spaced pay zones in a borehole comprising the steps of: perforating the spaced pay zones with a perforating apparatus from an outermost pay zone to an innermost pay zone; providing a coiled tubing reel and an injector adjacent the borehole; unreeling and injecting the coiled tubing downhole in the borehole to the outermost perforated pay zone; providing a packer about the coiled tubing inwardly of the outermost perforated pay zone;
injecting a fracturing material from the coiled tubing string into the outermost perforated pay zone, wherein the fracturing material is a viscoelastic surfactant; and injecting sand from said coiled tubing string into said outermost perforated pay zone after injection of said fracturing material to form a sand plug covering said outermost perforated pay zone.
A further broad aspect of the invention provides a process in a fracturing system for hydraulically fracturing wells having a plurality of spaced pay zones in a borehole, the system utilizing coiled tubing apparatus including a reel and an injector for inserting a coiled tubing string from the reel; said process including the steps of:
perforating said spaced pay zones with a perforating apparatus from the outermost pay zone to the innermost pay zone; providing a pair of spaced swab cups on the coiled tubing string for positioning on opposite sides of a selected perforated pay zone; inserting the coiled tubing string with the swab cups thereon within the borehole for positioning on opposed sides of said selected perforated pay zone; and injecting a fracturing material from the coiled tubing string within said selected perforated pay zone between said pair of swab cups, wherein the fracturing material is a viscoelastic surfactant.
A further broad aspect of the invention provides a process for hydraulically fracturing a pay zone in a well having a plurality of spaced pay zones in a borehole comprising the following steps: perforating the pay zones;
providing a coiled tubing string having a pair of spaced swab cups thereon for positioning on opposed sides of a selected pay zone; inserting the coiled tubing string with the pair of spaced swab cups thereon within the borehole and lowering the coiled tubing string to the selected pay zone with each one of the pair of the swab cups positioned on an opposed side of the selected pay zone; and injecting a fracturing material from the coiled tubing string within the selected pay zone between the pair of swab cups, wherein the fracturing material is a viscoelastic surfactant.
A further broad aspect of the invention provides a process for perforating and fracturing a plurality of spaced pay zones in a borehole for a well; the system utilizing coiled tubing apparatus including a reel and injector for inserting a coiled tubing string from the reel within the borehole; said process comprising the following steps:
(1) perforating the plurality of pay zones from an outermost pay zone; (2) providing a pair of swab cups on the coiled tubing string for positioning on opposed sides of the pay zones; (3) injecting the coiled tubing string with the swab cups thereon within the borehole for lowering the coiled tubing string to the outermost perforated pay zone with the swab cups positioned on opposed sides of said outermost pay zone; (4) injecting a fracturing material from the coiled tubing string into the outermost pay zone between the swab cups, wherein the fracturing material is a viscoelastic surfactant; (5) raising the coiled tubing string to the next adjacent pay zone with said swab cups on opposed sides of the next pay zone; and (6) injecting the fracturing material from the coiled tubing string into a next pay zone.
A further broad aspect of the invention provides a process for perforating and fracturing a plurality of vertically spaced pay zones in a shallow vertically extending gas well having a depth less than about 3,000 feet comprising the steps of: perforating the spaced pay zones with a perforating apparatus in a single trip of the perforating apparatus within the well; providing a coiled tubing apparatus including a reel and injector for inserting a coiled tubing string from the reel in the well;
positioning a pair of opposed spaced swab cups on the coiled tubing string for positioning on opposed sides of a selected pay zone for isolating the pay zone; inserting the coiled tubing within the well and positioning the swab cups on opposite sides of a lowermost perforated pay zone; injecting a fracturing material having a low friction from the coiled tubing string within the lowermost perforated pay zone; then raising the coiled tubing string to a next superjacent perforated pay zone with the swab cups isolating the next superjacent perforated pay zone; then injecting the fracturing material from the coiled tubing string within the next superjacent perforated pay zone; and repeating the steps of raising the coiled tubing string and injecting the fracturing material for all remaining perforated pay zones in the shallow well.
A further broad aspect of the invention provides a process for perforating and fracturing a plurality of vertically spaced pay zones in a shallow vertically extending well having a depth less than about 3,000 feet comprising the steps of: perforating the spaced pay zones with a perforating apparatus from an outermost pay zone to an innermost pay zone; providing a coiled tubing apparatus including a reel and injector for inserting a coiled tubing string from the reel in the well; positioning a packer on the coiled tubing string for positioning on the upper side of a selected pay zone for isolating the selected pay zone;
inserting the coiled tubing within the well and positioning the packer adjacent an upper side of a lowermost perforated pay zone; injecting a fracturing material having a low friction from the coiled tubing string within the lowermost perforated pay zone; then injecting sand from said coiled tubing string into the pay zone after injection of said fracturing material to form a sand plug covering the lowermost perforated pay zone; then raising the coiled tubing string to a next superjacent perforated pay zone with the packer isolating the next superjacent perforated pay zone; then injecting the fracturing material from the coiled tubing string within the next superjacent perforated pay zones; then injecting sand from said coiled tubing string into the next superjacent pay zone to form a next sand plug covering the next superjacent perforated pay zone; and repeating the steps of raising the coiled tubing string, injecting the fracturing material, and then injecting sand for all remaining perforated pay zones in the shallow well.
A further broad aspect of the invention provides a process for perforating and fracturing a plurality of vertically spaced pay zones in a shallow vertically extending gas well having a depth less than about 5,000 feet comprising the steps of: perforating the spaced pay zones with a perforating apparatus; providing a coiled tubing apparatus including a reel and an injector for inserting coiled tubing from the reel in the well; positioning a pair of opposed spaced swab cups on the coiled tubing for positioning on opposed sides of a selected pay zone for isolating the pay zone; inserting coiled tubing having an outer diameter of 2 3/8 inches within the well and positioning the swab cups on opposite sides of a lowermost perforated pay zone; injecting a fracturing material having a friction less than about 1,200 psi/1,000 feet from the coiled tubing within the lowermost perforated pay zone; then raising the coiled tubing to a next superjacent perforated pay zone with the swab cups isolating the next superjacent perforated pay zone; then injecting the fracturing material having a friction less than about 1,200 psi/1,000 feet from the coiled tubing within the next superjacent perforated pay zone; and repeating the steps of raising the coiled tubing and injecting said fracturing material for all remaining perforated pay zones in the shallow well.
Other features and advantages will be apparent from the following specification and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic view of a typical multiple pay zone wellbore showing perforating means suspended from coiled tubing for perforating each of the pay zones of the wellbore in a single trip of the coiled tubing;
Figure 2 is a schematic view of the multiple pay zone wellbore shown in Figure 1 but showing coiled tubing suspending a bottom hole assembly for hydraulic fracturing of each of the pay zones in sequence from the lowermost pay zone to the uppermost pay zone and showing the bottom hole assembly in position for hydraulic fracturing of the lowermost pay zone;
Figure 3 is an elevational view of a suitable bottom hole assembly suspended from the coiled tubing for hydraulic fracturing of the pay zones;
Figure 4 is a schematic view similar to Figure 2 but showing the bottom hole assembly in position for hydraulic fracturing of the second pay zone from the bottom of the wellbore with a sand plug within the wellbore covering the perforations in the lowermost pay zone which has been hydraulically fractured;
Figure 5 is a schematic view of the wellbore shown in Figures 2 and 4 with the fracturing operation completed and sand within the wellbore being washed out for production;
Figure 6 is a schematic view of another embodiment of the invention in which the coiled tubing fracturing process utilizes upper and lower swab cups for isolating each of the pay zones in sequence from the lowermost pay zone;
Figure 7 is a schematic view of a further embodiment of the invention in which the coiled tubing fracturing process utilizes only upper swab cups for isolation of a pay zone with a sand plug utilized for isolating the lower end of the zone after hydraulic fracturing;
Figure 8 is a schematic view of a further embodiment illustrating the coiled tubing fracturing process for a plurality of lateral bore portions extending to pay zones from a single vertical borehole; and Figure 9 is a schematic of another embodiment illustrating the coiled tubing fracturing process for a horizontal borehole having a plurality of separate pay zones.
DESCRIPTION OF THE INVENTION
This invention is directed particularly to a process of hydraulically fracturing a multiple pay zone wellbore with coiled tubing in one trip of the coiled tubing. The process also includes the perforation of the multiple pay zones with a wireline or coiled tubing prior to the hydraulic fracturing in a single pass of the wireline as shown in Figure 1.
A wellbore for an oil or gas well is generally indicated at 10 in an earth formation 12 and has a casing 14 connected to a wellhead generally indicated at 16. A coiled tubing string 18 is wound on a reel 20 and extends from reel 20 over a gooseneck 22 to an injector 24 positioned over wellhead 16 for injecting the coiled tubing string 18 through wellhead 16 within casing 14 as well known.
Suspended from the lower end of the coiled tubing string 18 are a plurality of perforating guns 26 connected by a cable 28. A wireline 30 positioned within coiled tubing 18 is connected to perforating guns 26 for selective detonation of perforating guns 26 from a surface location. In some instances, wireline 30 may be utilized without the coiled tubing 18 and suspend perforating guns 26. Perforated guns may be detonated individually or may be detonated simultaneously depending primarily on the configuration of the well.
Earth formation 12 has a plurality of spaced production or pay zones including a lowermost zone 32, an intermediate zone 34, and an uppermost zone 36. Zones 32, 34, and 36 are formed of an earth material having a high permeability in excess of 50 millidarcy for example. A
bridge plug 37 is positioned in casing 14 adjacent the bottom of casing 14 below lowermost pay zone 32. Casing 14 is perforated at pay zones 32, 34, 36 in a single pass of the coiled tubing string 18 commencing with the lowermost pay zone 32. Lower perforating gun or head 26 is detonated when aligned with pay zone 32. Coiled tubing string 18 is then raised until the intermediate perforating gun 26 is adjacent pay zone 34 for detonation. The coiled tubing string 18 is next raised until the uppermost perforating gun 26 is in alignment with pay zone 36 and is then detonated utilizing wireline 30. The casing 14 is then perforated along casing sections 38 for pay zones 32, 34, and 36 as shown particularly in Figure 2. If desired for some applications, perforating guns 26 may be initially aligned with pay zones 32, 34, 36 and detonated simultaneously.
As shown in Figure 2, coiled tubing string 18 has a bottom hole assembly generally indicated at 40 suspending within casing 14 adjacent the lowermost pay zone 32 and arranged for hydraulically fracturing lowermost pay zone 32 adjacent perforated casing section 38. As shown particularly in Figure 3, bottom hole assembly 40 includes a grapple connector 42 connected to tubing string 18 and a tension set packer indicated at 44. A tail pipe connector 46 is connected to packer 44 and a tail pipe 48 extends downwardly from tail pipe connector 46. A tension set packer which has been found to be satisfactory is a Baker Model ADl packer sold by Baker Hughes, Inc., of Houston, Texas. Packer 44 is shown schematically in set position above the upper end of lowermost pay zone 32 in Figure 3 and end tail pipe 48 extends downwardly therefrom.
The low friction fracturing material in the form of a slurry is discharged from tail pipe 48 at a predetermined pressure and volume for flowing into the permeable formation adjacent perforated casing section 38. After pay zone 32 has been fractured with the predetermined low friction fracturing material and stabilized with a predetermined amount of the fracturing material, the slurry system is switched to a flush position and sufficient sand is added to form a sand plug in casing 14. The pumping system is then shut down and the sand settles to form a sand plug shown at 50 in Figure 4 across the perforations adjacent the lower end of the perforated section 38 and extending above perforated section 38.
After it has been determined that sand plug 50 is in place, packer 44 is released and the bottom hole assembly 40 raised or pulled to the next pay zone 34.
Packer 44 is then set at a position about twenty (20) meters, for example, above the uppermost perforations in casing section 38. The process is then repeated for pay zone 34 as shown in Figure 4. The sand plug 50 for each pay zone 32, 34, 36 is sufficient to cover the perforations in each of the pay zones so that an adequate sand plug is provided for isolation of each of the pay zones. The sand plug is formed at the end of the fracturing process by increasing the sand concentration in the slurry to provide the desired sand plug. After the pump is shut down, the sand settles to form the sand plug across the adjacent perforations.
After providing the sand plug for pay zone 34, the tension packer 44 is released and the bottom hole assembly 40 raised to the next pay zone 36 for a repeat of the process. Any number of pay zones may be hydraulically fractured by the present process in a single trip of the coiled tubing string 18 and a sand plug is positioned at each pay zone. For the uppermost pay zone, an upper mechanical packer may not always be necessary as a hanger may be provided for wellhead 16 in some instances to provide sealing of the annulus as illustrated in Figure 5. After the fracturing process is completed, the coiled tubing assembly is removed from the borehole or well. The sand in the wellbore may be removed by another coiled tubing unit using air or water to wash the sand from the borehole as illustrated in Figure 5.
Referring now to Figure 6, the process of the present invention is shown with each pay zone 32, 34, 36 being isolated individually by opposed swap cups mounted on the coiled tubing string 18. A pair of inverted downwardly projecting swab cups 54 are mounted on coiled tubing string 18 for positioning above the upper side of pay zone 32 and a pair of upwardly directed swab cups 56 are mounted on coiled tubing string 18 for positioning below the lower side of pay zone 32. Swab cups 54, 56 do not have to be released and set for movement from one zone to another zone for isolating each zone individually and may be easily moved from one zone to another zone in a minimum of time by raising of tubing string 18. A suitable bottom hole assembly 59 is provided between upper and lower swab cups 54, 56 for discharge of the fracturing material into the adjacent formation.
Lower swab cups 56 are preferably spaced from upper swab cups 54 a distance at least equal to the thickness of the pay zone having the greatest thickness.
Thus, the distances between swab cups 54 and swab cups 56 do not have to be adjusted upon movement from one pay zone to another pay zone. Swab cups which have been found to be satisfactory for use with the present invention are sold by Progressive Technology of Langdon, Alberta, Canada.
As shown in the embodiment of Figure 7, coiled tubing string 18 has a pair of inverted downwardly directed upper swab cups 58 mounted thereon for positioning above the upper side of pay zone 32. A bottom hole assembly 60 extends downwardly from upper swab cups 58. A sand plug is utilized for isolation of the lower side of pay zone 32 as in the embodiment shown in Figures 1-5. Coiled tubing 18 and swab cups 58 may be easily moved to the next superjacent pay zone without any release or setting of a packer. The process as shown in the embodiments of Figures 1-7 utilizes a single perforated casing for a plurality of vertically spaced pay zones. As shown in Figure 8, the process of the present invention is shown for a borehole having a plurality of horizontally extending borehole portions defining pay zones 32A, 34A, and 36A. A vertical casing 18A has a plurality of lateral branches 35A, 37A, and 39A extending laterally from casing 14A within pay zones 32A, 34A, and 36A. Zones 32A, 34A, and 36A are hydraulically fractured in sequence. Innermost swab cups 54A and outermost swab cups 56A are mounted about coiled tubing 18A
from reel 20A on opposite sides of perforations 38A of casing branch 35A which forms the farthermost casing branch.
While outermost swab cups 56A are shown mounted on coiled tubing 18A, it may be desirable to provide a sand plug in lieu of outermost swab cups 56A as shown in Figure 7. After fracturing of pay zone 32A, pay zones 34A and 36A are fractured in a similar manner.
As shown in Figure 9, the process of the present invention is shown for a plurality of horizontally spaced pay zones 32B, 34B and 36B. Casing 14B has a plurality of perforated sections 38B in pay zones 32B, 34B and 36B and a bridge plug 37B adjacent the end of casing 14B. While farthermost swab cups 56B are shown mounted on tubing string 18B, it may be desired to substitute sand plugs for swab cups 56B as in the embodiment of Figure 7. Coiled tubing string 18B from reel 20B has inner swab cups 54B and outer swab cups 56B. Production or pay zones 32B, 34B
and 36B are hydraulically fractured in sequence with each pay zone being individually isolated by swab cups. As used in the specification and claims herein, the term "outermost"
pay zone is interpreted as including the lowermost and farthermost pay zones as shown in the various embodiments.
In all of the embodiments of this invention, the casing is preferably perforated in a single pass of the wireline or coiled tubing as shown and described in Figure 1, although in some instances multiple passes may be made.
The process of the present invention utilizes coiled tubing for hydraulic fracturing a formation having a plurality of separate pay or production zones to be individually fractured in a single pass of coiled tubing with each zone being isolated with sand plugs or swab cups.
In some instances, it might be desirable to provide hydraulic fracturing for a selected one of the plurality of pay zones such as might be desirable if a pay zone was previously bypassed. Also, selected fracturing might be provided for multiple lateral wells such as shown in Figure 8 of the invention. In some instances, the process may also be provided for an open or uncased borehole without perforation of the pay zones. The process is particularly adapted for relatively shallow wells such as less than about 8,000 feet and particularly for gas which might exist in bypassed pay zones. Heretofore, on new wells, a retrievable bridge plug was positioned below the bottom side of each of the pay zones which was relatively time consuming. For many applications of hydraulic fracturing with coiled tubing, a relatively shallow well or borehole less than about 3,000 feet is utilized with hydraulic fracturing at a pressure under about 7,500 psi.
Fiber-Based Additive For Friction Reduction A fracturing fluid which has been found to have low friction properties and is utilized with this invention is shown in U.S. Patent No. 5,501,275. U.S. Patent No. 5,501,275 shows a fiber-based additive that is used to control proppant flowback from a hydraulic fracture during production and to reduce surface pressure during injection.
The following friction calculations illustrate such a reduction:
Inj. Rate (Pounds of Tubing ID Op psi/1000 ft Proppant Added) PPA
18 9 2.44" 37 7 2.76" 48 32 5 2.70" 62 5 3.24" 9.5 6 2.75" 84 40 7 2.76" 13.8 However, even for comparable pipe sizes, injection rates and prop concs, a significant disparity in ~p is seen.
This is attributed to the difficulty in accurately estimating friction from surface pressures and a detailed calculation is required prior to utilization of the fiber-based additive for friction reduction although it is clearly established that the fiber-base additive shown in U.S.
Patent No. 5,501,275 reduces friction. The '275 patent includes a porous solid pack of fibers and proppant which reduces the energy consumption of equipment and provide a significant reduction in frictional forces. The fiber length is at least about 2 millimeters and the fiber diameter ranges between about 3 to 200 microns. Glass fibers are particularly preferred although carbon fibers are oftentimes preferred for harsh conditions. A proppant is normally utilized and may comprise a resin coated sand.
Resin coated sand and fibers provide a strong pack.
Viscoelastic Surfactant (VES) Fracturing Fluid Another fracturing material utilized with this invention which has been found to have a low friction is shown in U.S. Patent No. 5,551,516 dated September 3, 1996.
U.S. Patent No. 5,551,516 is directed to an aqueous viscoelastic surfactant (VES) fluid as a fracturing fluid.
Commonly used fracturing fluids consist of water and the use of a gelling agent. The gelling agent normally is a polymer, such as guar or its derivatives. This polymer exists in the form of long molecular chains. These chains are then cross-linked to enhance the viscosity of a fracturing fluid. This increased viscosity is needed during fracturing but is undesirable for productivity of the wellbore and is preferably removed following the fracturing operation. This however is not easy and more than often, gel residue is left behind in the fracturing, which affects the well productivity.
A viscoelastic surfactant is a non-polymeric fluid. It relies on the use of a surfactant to develop viscosity. In contrast to the x-linked structure of a polymeric fluid, a VES fluid develops viscosity through the aggregation of which is referred to as micelles. This micellar structure however deteriorates when brought in contact with a hydrocarbon. The fluid thus naturally looses viscosity during production, leaving behind a clean proppant pack in the fracture.
The friction reducing characteristics of VES
fluids have been shown in field practice. A comparative set of friction numbers for the VES fluid and a polymeric system (low-guar) identified as YF120LG, a low guar borate cross-linked fracture fluid sold by Dowell Schlumberger of Houston, Texas, with an injection rate of 9.5 bpm (barrels per minute) and a 1.34 inch internal diameter of coiled tubing is shown below:
Fluid Friction (psi/1000 ft) YF120LG 3,460 VES 1,170 .
VES is believed to have a low friction pressure resulting from a different rheological structure. VES
provides a 100% retained permeability to permit a fracture treatment to be designed with a relatively small proppant concentration.
The aqueous viscoelastic surfactant comprises water, an inorganic salt stabilizer, a surfactant/thickener and an organic salt or alcohol. The fracturing fluid may optionally contain a gas such as air, nitrogen or carbon dioxide to provide an energized fluid or a foam. A small group of surfactants having unique viscoelastic properties make them of high interest for use in fracturing applications and find particular utility in forming fracturing fluids for fracturing treatment of high permeability subterranean formations.
In addition to the viscoelastic surfactant, the aqueous fracturing fluid requires a sufficient quantity of at least one water soluble inorganic salt to effect formation stability. Typically, water soluble potassium and ammonium salts, such as potassium chloride and ammonium chloride are employed. Additionally, calcium chloride, calcium bromide and zinc halide salts may also be used.
Formation stability and in particular clay stability is achieved at a concentration level of a few percent by weight and as such the density of the fluid is not significantly altered by the presence of the inorganic salt unless fluid density becomes an important consideration, at which point, heavier inorganic salts may be employed.
A sufficient quantity of at least one surfactant/thickener soluble in the aqueous salt solution is employed to effect, in combination with an organic salt and/or alcohol, sufficient viscosity to suspend proppant during placement.
A sufficient quantity of a water soluble organic salt and/or alcohol is employed to effect, in combination with the thickener, the desired viscoelastic properties.
Preferably the organic salt is water soluble carboxylate salt such as sodium or potassium salicylate or the like.
Preferably the alcohol is a cosurfactant, typically a C4 to C12 aliphatic alcohol.
Other fracturing fluids Two other fracturing fluids that exhibit a relatively lower friction pressure can also be used with coiled tubing fracturing operations. The first of these is the Xanthan-polymer based fracturing fluid. This fluid dampens turbulence which is developed at large flow velocities. Turbulence is the primary reason for friction pressure losses in the tubing during injection. A second such friction reducing fluid is the synergistic polymer blend. This fluid system is developed by mixing a particular proportion of the Xanthan and guar polymers.
These fluids have a lower viscosity than YF120LG at the high shear rate that are encountered within the coiled tubing.
This lower viscosity is primarily responsible for the reduced friction during injection.
Coiled tubing fracturing can alternatively be performed with additives that are included with the fracturing fluid to reduce friction during fluid injection.
One such additive is sold under the name "UltraLube", and is commercially manufactured by Stavanger Fluids of Stavanger, Norway. The Ultralube additive reduces fluid friction by forming a lubricating coating on the internal walls of the coiled tubing which reduces the fluid drag and hence friction pressure losses.
As indicated previously, a fracturing fluid utilized with coiled tubing in a fracturing operation is required to have a low friction which may vary dependent primarily on the diameter of the coiled tubing and the depth of the outermost pay zone. The following table sets forth the maximum friction in a fracturing fluid which can obtain satisfactory results for a particular OD of coiled tubing and a particular depth of the pay zone.
Coiled Tubing OD Depth of Pay Zone Maximum Friction (inches) (feet) (psi/1,000 feet) 1 3/4 3,000 4,560 2 3/8 3,000 1,680 1 3/4 5,000 4,200 2 3/8 5,000 1,200 1 3/4 8,000 3,700 2 3/8 8,000 850 Specific Example For testing of the process, a four well project with each of the wells having four pay zones to be fractured individually was selected having a shallow well depth of about 1,500 feet and utilizing coiled tubing of 2 3/8 inch outer diameter. Each of the individual zones are isolated by a mechanical packer adjacent the upper end of each zone and a sand plug adjacent the lower end of each zone. Each of the pay zones was perforated prior to the beginning of the fracturing operation utilizing coiled tubing in one trip. Two types of packers were utilized as the upper packer. One of the packers was a Baker Model ADI Tension Packer sold by Baker Hughes, Inc. of Houston, Texas. The other upper packer was an inverted swab cup arrangement utilizing one or two downwardly facing cups in series to allow easy movement of the coiled tubing from one zone to another zone without having to mechanically set and upset the packer. A one meter tail pipe was suspended from the end of the coiled tubing. The fracturing material was pumped at a rate between about 1 and 1 ~ cubic meters a minute to initiate fracture breakdown and then the rate was increased for the remainder of the treatment to about 2 cubic meters per minute. The well was fractured with a suitable amount of fluid and proppant varying with the selected zone and increasing the concentration of sand. At the end of the pumping of the fractured fluid, the pump was switched to a flush position and sand was added to provide a suitable sand plug of about 20 to 30 meters in height. when the pump is shut down, the sand settled to create a sand plug across the perforations of the zone which was fractured. After testing of the sand plug, the packer was released and lifted to the next zone for hydraulic fracturing. The sand plug for each of the four pay zones was effective and a relatively fast sand placement was achieved.
In another test, an inverted swab cup was positioned about the coiled tubing above the pay zone.
Thus, the utilization of coiled tubing for fracturing multiple relatively shallow pay zones with isolation provided by a mechanical packer and a sand plug for each zone was successfully completed. Further, utilizing swab cups in lieu of the mechanical packer and later in lieu of the sand plugs were found to be highly effective and resulted in a minimum of time in hydraulic fracturing of the plurality of zones as movement from one zone to another zone was minimized.
While preferred embodiments of the present invention have been illustrated in detail, it is apparent that modifications and adaptations of the preferred embodiments will occur to those skilled in the art.
However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention as set forth in the following claims.
A further broad aspect of the invention provides a process for perforating and fracturing a plurality of vertically spaced pay zones in a shallow vertically extending gas well having a depth less than about 3,000 feet comprising the steps of: perforating the spaced pay zones with a perforating apparatus in a single trip of the perforating apparatus within the well; providing a coiled tubing apparatus including a reel and injector for inserting a coiled tubing string from the reel in the well;
positioning a pair of opposed spaced swab cups on the coiled tubing string for positioning on opposed sides of a selected pay zone for isolating the pay zone; inserting the coiled tubing within the well and positioning the swab cups on opposite sides of a lowermost perforated pay zone; injecting a fracturing material having a low friction from the coiled tubing string within the lowermost perforated pay zone; then raising the coiled tubing string to a next superjacent perforated pay zone with the swab cups isolating the next superjacent perforated pay zone; then injecting the fracturing material from the coiled tubing string within the next superjacent perforated pay zone; and repeating the steps of raising the coiled tubing string and injecting the fracturing material for all remaining perforated pay zones in the shallow well.
A further broad aspect of the invention provides a process for perforating and fracturing a plurality of vertically spaced pay zones in a shallow vertically extending well having a depth less than about 3,000 feet comprising the steps of: perforating the spaced pay zones with a perforating apparatus from an outermost pay zone to an innermost pay zone; providing a coiled tubing apparatus including a reel and injector for inserting a coiled tubing string from the reel in the well; positioning a packer on the coiled tubing string for positioning on the upper side of a selected pay zone for isolating the selected pay zone;
inserting the coiled tubing within the well and positioning the packer adjacent an upper side of a lowermost perforated pay zone; injecting a fracturing material having a low friction from the coiled tubing string within the lowermost perforated pay zone; then injecting sand from said coiled tubing string into the pay zone after injection of said fracturing material to form a sand plug covering the lowermost perforated pay zone; then raising the coiled tubing string to a next superjacent perforated pay zone with the packer isolating the next superjacent perforated pay zone; then injecting the fracturing material from the coiled tubing string within the next superjacent perforated pay zones; then injecting sand from said coiled tubing string into the next superjacent pay zone to form a next sand plug covering the next superjacent perforated pay zone; and repeating the steps of raising the coiled tubing string, injecting the fracturing material, and then injecting sand for all remaining perforated pay zones in the shallow well.
A further broad aspect of the invention provides a process for perforating and fracturing a plurality of vertically spaced pay zones in a shallow vertically extending gas well having a depth less than about 5,000 feet comprising the steps of: perforating the spaced pay zones with a perforating apparatus; providing a coiled tubing apparatus including a reel and an injector for inserting coiled tubing from the reel in the well; positioning a pair of opposed spaced swab cups on the coiled tubing for positioning on opposed sides of a selected pay zone for isolating the pay zone; inserting coiled tubing having an outer diameter of 2 3/8 inches within the well and positioning the swab cups on opposite sides of a lowermost perforated pay zone; injecting a fracturing material having a friction less than about 1,200 psi/1,000 feet from the coiled tubing within the lowermost perforated pay zone; then raising the coiled tubing to a next superjacent perforated pay zone with the swab cups isolating the next superjacent perforated pay zone; then injecting the fracturing material having a friction less than about 1,200 psi/1,000 feet from the coiled tubing within the next superjacent perforated pay zone; and repeating the steps of raising the coiled tubing and injecting said fracturing material for all remaining perforated pay zones in the shallow well.
Other features and advantages will be apparent from the following specification and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic view of a typical multiple pay zone wellbore showing perforating means suspended from coiled tubing for perforating each of the pay zones of the wellbore in a single trip of the coiled tubing;
Figure 2 is a schematic view of the multiple pay zone wellbore shown in Figure 1 but showing coiled tubing suspending a bottom hole assembly for hydraulic fracturing of each of the pay zones in sequence from the lowermost pay zone to the uppermost pay zone and showing the bottom hole assembly in position for hydraulic fracturing of the lowermost pay zone;
Figure 3 is an elevational view of a suitable bottom hole assembly suspended from the coiled tubing for hydraulic fracturing of the pay zones;
Figure 4 is a schematic view similar to Figure 2 but showing the bottom hole assembly in position for hydraulic fracturing of the second pay zone from the bottom of the wellbore with a sand plug within the wellbore covering the perforations in the lowermost pay zone which has been hydraulically fractured;
Figure 5 is a schematic view of the wellbore shown in Figures 2 and 4 with the fracturing operation completed and sand within the wellbore being washed out for production;
Figure 6 is a schematic view of another embodiment of the invention in which the coiled tubing fracturing process utilizes upper and lower swab cups for isolating each of the pay zones in sequence from the lowermost pay zone;
Figure 7 is a schematic view of a further embodiment of the invention in which the coiled tubing fracturing process utilizes only upper swab cups for isolation of a pay zone with a sand plug utilized for isolating the lower end of the zone after hydraulic fracturing;
Figure 8 is a schematic view of a further embodiment illustrating the coiled tubing fracturing process for a plurality of lateral bore portions extending to pay zones from a single vertical borehole; and Figure 9 is a schematic of another embodiment illustrating the coiled tubing fracturing process for a horizontal borehole having a plurality of separate pay zones.
DESCRIPTION OF THE INVENTION
This invention is directed particularly to a process of hydraulically fracturing a multiple pay zone wellbore with coiled tubing in one trip of the coiled tubing. The process also includes the perforation of the multiple pay zones with a wireline or coiled tubing prior to the hydraulic fracturing in a single pass of the wireline as shown in Figure 1.
A wellbore for an oil or gas well is generally indicated at 10 in an earth formation 12 and has a casing 14 connected to a wellhead generally indicated at 16. A coiled tubing string 18 is wound on a reel 20 and extends from reel 20 over a gooseneck 22 to an injector 24 positioned over wellhead 16 for injecting the coiled tubing string 18 through wellhead 16 within casing 14 as well known.
Suspended from the lower end of the coiled tubing string 18 are a plurality of perforating guns 26 connected by a cable 28. A wireline 30 positioned within coiled tubing 18 is connected to perforating guns 26 for selective detonation of perforating guns 26 from a surface location. In some instances, wireline 30 may be utilized without the coiled tubing 18 and suspend perforating guns 26. Perforated guns may be detonated individually or may be detonated simultaneously depending primarily on the configuration of the well.
Earth formation 12 has a plurality of spaced production or pay zones including a lowermost zone 32, an intermediate zone 34, and an uppermost zone 36. Zones 32, 34, and 36 are formed of an earth material having a high permeability in excess of 50 millidarcy for example. A
bridge plug 37 is positioned in casing 14 adjacent the bottom of casing 14 below lowermost pay zone 32. Casing 14 is perforated at pay zones 32, 34, 36 in a single pass of the coiled tubing string 18 commencing with the lowermost pay zone 32. Lower perforating gun or head 26 is detonated when aligned with pay zone 32. Coiled tubing string 18 is then raised until the intermediate perforating gun 26 is adjacent pay zone 34 for detonation. The coiled tubing string 18 is next raised until the uppermost perforating gun 26 is in alignment with pay zone 36 and is then detonated utilizing wireline 30. The casing 14 is then perforated along casing sections 38 for pay zones 32, 34, and 36 as shown particularly in Figure 2. If desired for some applications, perforating guns 26 may be initially aligned with pay zones 32, 34, 36 and detonated simultaneously.
As shown in Figure 2, coiled tubing string 18 has a bottom hole assembly generally indicated at 40 suspending within casing 14 adjacent the lowermost pay zone 32 and arranged for hydraulically fracturing lowermost pay zone 32 adjacent perforated casing section 38. As shown particularly in Figure 3, bottom hole assembly 40 includes a grapple connector 42 connected to tubing string 18 and a tension set packer indicated at 44. A tail pipe connector 46 is connected to packer 44 and a tail pipe 48 extends downwardly from tail pipe connector 46. A tension set packer which has been found to be satisfactory is a Baker Model ADl packer sold by Baker Hughes, Inc., of Houston, Texas. Packer 44 is shown schematically in set position above the upper end of lowermost pay zone 32 in Figure 3 and end tail pipe 48 extends downwardly therefrom.
The low friction fracturing material in the form of a slurry is discharged from tail pipe 48 at a predetermined pressure and volume for flowing into the permeable formation adjacent perforated casing section 38. After pay zone 32 has been fractured with the predetermined low friction fracturing material and stabilized with a predetermined amount of the fracturing material, the slurry system is switched to a flush position and sufficient sand is added to form a sand plug in casing 14. The pumping system is then shut down and the sand settles to form a sand plug shown at 50 in Figure 4 across the perforations adjacent the lower end of the perforated section 38 and extending above perforated section 38.
After it has been determined that sand plug 50 is in place, packer 44 is released and the bottom hole assembly 40 raised or pulled to the next pay zone 34.
Packer 44 is then set at a position about twenty (20) meters, for example, above the uppermost perforations in casing section 38. The process is then repeated for pay zone 34 as shown in Figure 4. The sand plug 50 for each pay zone 32, 34, 36 is sufficient to cover the perforations in each of the pay zones so that an adequate sand plug is provided for isolation of each of the pay zones. The sand plug is formed at the end of the fracturing process by increasing the sand concentration in the slurry to provide the desired sand plug. After the pump is shut down, the sand settles to form the sand plug across the adjacent perforations.
After providing the sand plug for pay zone 34, the tension packer 44 is released and the bottom hole assembly 40 raised to the next pay zone 36 for a repeat of the process. Any number of pay zones may be hydraulically fractured by the present process in a single trip of the coiled tubing string 18 and a sand plug is positioned at each pay zone. For the uppermost pay zone, an upper mechanical packer may not always be necessary as a hanger may be provided for wellhead 16 in some instances to provide sealing of the annulus as illustrated in Figure 5. After the fracturing process is completed, the coiled tubing assembly is removed from the borehole or well. The sand in the wellbore may be removed by another coiled tubing unit using air or water to wash the sand from the borehole as illustrated in Figure 5.
Referring now to Figure 6, the process of the present invention is shown with each pay zone 32, 34, 36 being isolated individually by opposed swap cups mounted on the coiled tubing string 18. A pair of inverted downwardly projecting swab cups 54 are mounted on coiled tubing string 18 for positioning above the upper side of pay zone 32 and a pair of upwardly directed swab cups 56 are mounted on coiled tubing string 18 for positioning below the lower side of pay zone 32. Swab cups 54, 56 do not have to be released and set for movement from one zone to another zone for isolating each zone individually and may be easily moved from one zone to another zone in a minimum of time by raising of tubing string 18. A suitable bottom hole assembly 59 is provided between upper and lower swab cups 54, 56 for discharge of the fracturing material into the adjacent formation.
Lower swab cups 56 are preferably spaced from upper swab cups 54 a distance at least equal to the thickness of the pay zone having the greatest thickness.
Thus, the distances between swab cups 54 and swab cups 56 do not have to be adjusted upon movement from one pay zone to another pay zone. Swab cups which have been found to be satisfactory for use with the present invention are sold by Progressive Technology of Langdon, Alberta, Canada.
As shown in the embodiment of Figure 7, coiled tubing string 18 has a pair of inverted downwardly directed upper swab cups 58 mounted thereon for positioning above the upper side of pay zone 32. A bottom hole assembly 60 extends downwardly from upper swab cups 58. A sand plug is utilized for isolation of the lower side of pay zone 32 as in the embodiment shown in Figures 1-5. Coiled tubing 18 and swab cups 58 may be easily moved to the next superjacent pay zone without any release or setting of a packer. The process as shown in the embodiments of Figures 1-7 utilizes a single perforated casing for a plurality of vertically spaced pay zones. As shown in Figure 8, the process of the present invention is shown for a borehole having a plurality of horizontally extending borehole portions defining pay zones 32A, 34A, and 36A. A vertical casing 18A has a plurality of lateral branches 35A, 37A, and 39A extending laterally from casing 14A within pay zones 32A, 34A, and 36A. Zones 32A, 34A, and 36A are hydraulically fractured in sequence. Innermost swab cups 54A and outermost swab cups 56A are mounted about coiled tubing 18A
from reel 20A on opposite sides of perforations 38A of casing branch 35A which forms the farthermost casing branch.
While outermost swab cups 56A are shown mounted on coiled tubing 18A, it may be desirable to provide a sand plug in lieu of outermost swab cups 56A as shown in Figure 7. After fracturing of pay zone 32A, pay zones 34A and 36A are fractured in a similar manner.
As shown in Figure 9, the process of the present invention is shown for a plurality of horizontally spaced pay zones 32B, 34B and 36B. Casing 14B has a plurality of perforated sections 38B in pay zones 32B, 34B and 36B and a bridge plug 37B adjacent the end of casing 14B. While farthermost swab cups 56B are shown mounted on tubing string 18B, it may be desired to substitute sand plugs for swab cups 56B as in the embodiment of Figure 7. Coiled tubing string 18B from reel 20B has inner swab cups 54B and outer swab cups 56B. Production or pay zones 32B, 34B
and 36B are hydraulically fractured in sequence with each pay zone being individually isolated by swab cups. As used in the specification and claims herein, the term "outermost"
pay zone is interpreted as including the lowermost and farthermost pay zones as shown in the various embodiments.
In all of the embodiments of this invention, the casing is preferably perforated in a single pass of the wireline or coiled tubing as shown and described in Figure 1, although in some instances multiple passes may be made.
The process of the present invention utilizes coiled tubing for hydraulic fracturing a formation having a plurality of separate pay or production zones to be individually fractured in a single pass of coiled tubing with each zone being isolated with sand plugs or swab cups.
In some instances, it might be desirable to provide hydraulic fracturing for a selected one of the plurality of pay zones such as might be desirable if a pay zone was previously bypassed. Also, selected fracturing might be provided for multiple lateral wells such as shown in Figure 8 of the invention. In some instances, the process may also be provided for an open or uncased borehole without perforation of the pay zones. The process is particularly adapted for relatively shallow wells such as less than about 8,000 feet and particularly for gas which might exist in bypassed pay zones. Heretofore, on new wells, a retrievable bridge plug was positioned below the bottom side of each of the pay zones which was relatively time consuming. For many applications of hydraulic fracturing with coiled tubing, a relatively shallow well or borehole less than about 3,000 feet is utilized with hydraulic fracturing at a pressure under about 7,500 psi.
Fiber-Based Additive For Friction Reduction A fracturing fluid which has been found to have low friction properties and is utilized with this invention is shown in U.S. Patent No. 5,501,275. U.S. Patent No. 5,501,275 shows a fiber-based additive that is used to control proppant flowback from a hydraulic fracture during production and to reduce surface pressure during injection.
The following friction calculations illustrate such a reduction:
Inj. Rate (Pounds of Tubing ID Op psi/1000 ft Proppant Added) PPA
18 9 2.44" 37 7 2.76" 48 32 5 2.70" 62 5 3.24" 9.5 6 2.75" 84 40 7 2.76" 13.8 However, even for comparable pipe sizes, injection rates and prop concs, a significant disparity in ~p is seen.
This is attributed to the difficulty in accurately estimating friction from surface pressures and a detailed calculation is required prior to utilization of the fiber-based additive for friction reduction although it is clearly established that the fiber-base additive shown in U.S.
Patent No. 5,501,275 reduces friction. The '275 patent includes a porous solid pack of fibers and proppant which reduces the energy consumption of equipment and provide a significant reduction in frictional forces. The fiber length is at least about 2 millimeters and the fiber diameter ranges between about 3 to 200 microns. Glass fibers are particularly preferred although carbon fibers are oftentimes preferred for harsh conditions. A proppant is normally utilized and may comprise a resin coated sand.
Resin coated sand and fibers provide a strong pack.
Viscoelastic Surfactant (VES) Fracturing Fluid Another fracturing material utilized with this invention which has been found to have a low friction is shown in U.S. Patent No. 5,551,516 dated September 3, 1996.
U.S. Patent No. 5,551,516 is directed to an aqueous viscoelastic surfactant (VES) fluid as a fracturing fluid.
Commonly used fracturing fluids consist of water and the use of a gelling agent. The gelling agent normally is a polymer, such as guar or its derivatives. This polymer exists in the form of long molecular chains. These chains are then cross-linked to enhance the viscosity of a fracturing fluid. This increased viscosity is needed during fracturing but is undesirable for productivity of the wellbore and is preferably removed following the fracturing operation. This however is not easy and more than often, gel residue is left behind in the fracturing, which affects the well productivity.
A viscoelastic surfactant is a non-polymeric fluid. It relies on the use of a surfactant to develop viscosity. In contrast to the x-linked structure of a polymeric fluid, a VES fluid develops viscosity through the aggregation of which is referred to as micelles. This micellar structure however deteriorates when brought in contact with a hydrocarbon. The fluid thus naturally looses viscosity during production, leaving behind a clean proppant pack in the fracture.
The friction reducing characteristics of VES
fluids have been shown in field practice. A comparative set of friction numbers for the VES fluid and a polymeric system (low-guar) identified as YF120LG, a low guar borate cross-linked fracture fluid sold by Dowell Schlumberger of Houston, Texas, with an injection rate of 9.5 bpm (barrels per minute) and a 1.34 inch internal diameter of coiled tubing is shown below:
Fluid Friction (psi/1000 ft) YF120LG 3,460 VES 1,170 .
VES is believed to have a low friction pressure resulting from a different rheological structure. VES
provides a 100% retained permeability to permit a fracture treatment to be designed with a relatively small proppant concentration.
The aqueous viscoelastic surfactant comprises water, an inorganic salt stabilizer, a surfactant/thickener and an organic salt or alcohol. The fracturing fluid may optionally contain a gas such as air, nitrogen or carbon dioxide to provide an energized fluid or a foam. A small group of surfactants having unique viscoelastic properties make them of high interest for use in fracturing applications and find particular utility in forming fracturing fluids for fracturing treatment of high permeability subterranean formations.
In addition to the viscoelastic surfactant, the aqueous fracturing fluid requires a sufficient quantity of at least one water soluble inorganic salt to effect formation stability. Typically, water soluble potassium and ammonium salts, such as potassium chloride and ammonium chloride are employed. Additionally, calcium chloride, calcium bromide and zinc halide salts may also be used.
Formation stability and in particular clay stability is achieved at a concentration level of a few percent by weight and as such the density of the fluid is not significantly altered by the presence of the inorganic salt unless fluid density becomes an important consideration, at which point, heavier inorganic salts may be employed.
A sufficient quantity of at least one surfactant/thickener soluble in the aqueous salt solution is employed to effect, in combination with an organic salt and/or alcohol, sufficient viscosity to suspend proppant during placement.
A sufficient quantity of a water soluble organic salt and/or alcohol is employed to effect, in combination with the thickener, the desired viscoelastic properties.
Preferably the organic salt is water soluble carboxylate salt such as sodium or potassium salicylate or the like.
Preferably the alcohol is a cosurfactant, typically a C4 to C12 aliphatic alcohol.
Other fracturing fluids Two other fracturing fluids that exhibit a relatively lower friction pressure can also be used with coiled tubing fracturing operations. The first of these is the Xanthan-polymer based fracturing fluid. This fluid dampens turbulence which is developed at large flow velocities. Turbulence is the primary reason for friction pressure losses in the tubing during injection. A second such friction reducing fluid is the synergistic polymer blend. This fluid system is developed by mixing a particular proportion of the Xanthan and guar polymers.
These fluids have a lower viscosity than YF120LG at the high shear rate that are encountered within the coiled tubing.
This lower viscosity is primarily responsible for the reduced friction during injection.
Coiled tubing fracturing can alternatively be performed with additives that are included with the fracturing fluid to reduce friction during fluid injection.
One such additive is sold under the name "UltraLube", and is commercially manufactured by Stavanger Fluids of Stavanger, Norway. The Ultralube additive reduces fluid friction by forming a lubricating coating on the internal walls of the coiled tubing which reduces the fluid drag and hence friction pressure losses.
As indicated previously, a fracturing fluid utilized with coiled tubing in a fracturing operation is required to have a low friction which may vary dependent primarily on the diameter of the coiled tubing and the depth of the outermost pay zone. The following table sets forth the maximum friction in a fracturing fluid which can obtain satisfactory results for a particular OD of coiled tubing and a particular depth of the pay zone.
Coiled Tubing OD Depth of Pay Zone Maximum Friction (inches) (feet) (psi/1,000 feet) 1 3/4 3,000 4,560 2 3/8 3,000 1,680 1 3/4 5,000 4,200 2 3/8 5,000 1,200 1 3/4 8,000 3,700 2 3/8 8,000 850 Specific Example For testing of the process, a four well project with each of the wells having four pay zones to be fractured individually was selected having a shallow well depth of about 1,500 feet and utilizing coiled tubing of 2 3/8 inch outer diameter. Each of the individual zones are isolated by a mechanical packer adjacent the upper end of each zone and a sand plug adjacent the lower end of each zone. Each of the pay zones was perforated prior to the beginning of the fracturing operation utilizing coiled tubing in one trip. Two types of packers were utilized as the upper packer. One of the packers was a Baker Model ADI Tension Packer sold by Baker Hughes, Inc. of Houston, Texas. The other upper packer was an inverted swab cup arrangement utilizing one or two downwardly facing cups in series to allow easy movement of the coiled tubing from one zone to another zone without having to mechanically set and upset the packer. A one meter tail pipe was suspended from the end of the coiled tubing. The fracturing material was pumped at a rate between about 1 and 1 ~ cubic meters a minute to initiate fracture breakdown and then the rate was increased for the remainder of the treatment to about 2 cubic meters per minute. The well was fractured with a suitable amount of fluid and proppant varying with the selected zone and increasing the concentration of sand. At the end of the pumping of the fractured fluid, the pump was switched to a flush position and sand was added to provide a suitable sand plug of about 20 to 30 meters in height. when the pump is shut down, the sand settled to create a sand plug across the perforations of the zone which was fractured. After testing of the sand plug, the packer was released and lifted to the next zone for hydraulic fracturing. The sand plug for each of the four pay zones was effective and a relatively fast sand placement was achieved.
In another test, an inverted swab cup was positioned about the coiled tubing above the pay zone.
Thus, the utilization of coiled tubing for fracturing multiple relatively shallow pay zones with isolation provided by a mechanical packer and a sand plug for each zone was successfully completed. Further, utilizing swab cups in lieu of the mechanical packer and later in lieu of the sand plugs were found to be highly effective and resulted in a minimum of time in hydraulic fracturing of the plurality of zones as movement from one zone to another zone was minimized.
While preferred embodiments of the present invention have been illustrated in detail, it is apparent that modifications and adaptations of the preferred embodiments will occur to those skilled in the art.
However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention as set forth in the following claims.
Claims (36)
1. A process in a fracturing system for fracturing wells having a pay zone in a borehole, the system utilizing coiled tubing wound on a reel and an injector for inserting a coiled tubing string from the reel within the borehole;
said process comprising the following steps:
lowering the coiled tubing string within the borehole to the pay zone;
providing a packer about the coiled tubing inwardly of the pay zone;
injecting a fracturing material from the coiled tubing string into the perforated pay zone, wherein the fracturing material is a viscoelastic surfactant; and injecting sand from said coiled tubing string into the pay zone after injection of said fracturing material to form a sand plug covering the pay zone.
said process comprising the following steps:
lowering the coiled tubing string within the borehole to the pay zone;
providing a packer about the coiled tubing inwardly of the pay zone;
injecting a fracturing material from the coiled tubing string into the perforated pay zone, wherein the fracturing material is a viscoelastic surfactant; and injecting sand from said coiled tubing string into the pay zone after injection of said fracturing material to form a sand plug covering the pay zone.
2. The process as set forth in claim 1 including the step of:
providing a wireline and a perforating head at a lower end of the wireline;
injecting the wireline downhole to the pay zone;
and perforating the pay zone with the perforating head.
providing a wireline and a perforating head at a lower end of the wireline;
injecting the wireline downhole to the pay zone;
and perforating the pay zone with the perforating head.
3. A process in a fracturing system for fracturing gas wells and having a plurality of spaced pay zones in a borehole, the system utilizing coiled tubing apparatus including a reel and an injector for inserting a coiled tubing string from the reel within the borehole; said process comprising the following steps:
perforating a plurality of pay zones from a farthermost pay zone;
injecting the coiled tubing string within the borehole for lowering the coiled tubing string to an outermost perforated pay zone;
providing a packer about the coiled tubing string inwardly of the outermost perforated pay zone;
injecting a fracturing material from the coiled tubing string into the outermost perforated pay zone, wherein the fracturing material is a viscoelastic surfactant; and injecting sand from said coiled tubing string after injection of said fracturing material to form a sand plug covering the outermost perforated pay zone.
perforating a plurality of pay zones from a farthermost pay zone;
injecting the coiled tubing string within the borehole for lowering the coiled tubing string to an outermost perforated pay zone;
providing a packer about the coiled tubing string inwardly of the outermost perforated pay zone;
injecting a fracturing material from the coiled tubing string into the outermost perforated pay zone, wherein the fracturing material is a viscoelastic surfactant; and injecting sand from said coiled tubing string after injection of said fracturing material to form a sand plug covering the outermost perforated pay zone.
4. The process as set forth in claim 3 further comprising the steps of:
releasing said packer;
then lifting said coiled tubing string and packer to a next perforated pay zone for positioning said packer inwardly of a next pay zone;
then establishing said packer;
next injecting fracturing material from the coiled tubing string into said next perforated pay zone; and then injecting sand from said coiled tubing string to form a next sand plug covering said next perforated pay zone.
releasing said packer;
then lifting said coiled tubing string and packer to a next perforated pay zone for positioning said packer inwardly of a next pay zone;
then establishing said packer;
next injecting fracturing material from the coiled tubing string into said next perforated pay zone; and then injecting sand from said coiled tubing string to form a next sand plug covering said next perforated pay zone.
5. The process as set forth in claim 4 further comprising the steps of:
repeating the steps set forth in claim 4 for the remaining perforated pay zones.
repeating the steps set forth in claim 4 for the remaining perforated pay zones.
6. The process as set forth in claim 3 for fracturing an innermost perforated pay zone further including the steps of:
lifting said coiled tubing string to said innermost perforated pay zone;
injecting the fracturing material from the coiled tubing string into the innermost perforated pay zone without setting of the packer; and then injecting sand from said coiled tubing string after injection of said fracturing material to form an innermost sand plug covering said innermost perforated pay zone.
lifting said coiled tubing string to said innermost perforated pay zone;
injecting the fracturing material from the coiled tubing string into the innermost perforated pay zone without setting of the packer; and then injecting sand from said coiled tubing string after injection of said fracturing material to form an innermost sand plug covering said innermost perforated pay zone.
7. A process for perforating and fracturing shallow gas wells having a plurality of spaced pay zones in a borehole comprising the steps of:
perforating the spaced pay zones with a perforating apparatus from an outermost pay zone to an innermost pay zone;
providing a coiled tubing reel and an injector adjacent the borehole;
unreeling and injecting the coiled tubing downhole in the borehole to the outermost perforated pay zone;
providing a packer about the coiled tubing inwardly of the outermost perforated pay zone;
injecting a fracturing material from the coiled tubing string into the outermost perforated pay zone, wherein the fracturing material is a viscoelastic surfactant; and injecting sand from said coiled tubing string into said outermost perforated pay zone after injection of said fracturing material to form a sand plug covering said outermost perforated pay zone.
perforating the spaced pay zones with a perforating apparatus from an outermost pay zone to an innermost pay zone;
providing a coiled tubing reel and an injector adjacent the borehole;
unreeling and injecting the coiled tubing downhole in the borehole to the outermost perforated pay zone;
providing a packer about the coiled tubing inwardly of the outermost perforated pay zone;
injecting a fracturing material from the coiled tubing string into the outermost perforated pay zone, wherein the fracturing material is a viscoelastic surfactant; and injecting sand from said coiled tubing string into said outermost perforated pay zone after injection of said fracturing material to form a sand plug covering said outermost perforated pay zone.
8. The process as set forth in claim 7 including the steps of:
releasing said packer;
then lifting said coiled tubing string and packer to a next perforated pay zone for positioning said packer above the next perforated pay zone;
then setting said packer;
next injecting fracturing material from the coiled tubing string into said next perforated pay zone; and then injecting sand form said coiled tubing string to from a sand plug covering said next perforated pay zone.
releasing said packer;
then lifting said coiled tubing string and packer to a next perforated pay zone for positioning said packer above the next perforated pay zone;
then setting said packer;
next injecting fracturing material from the coiled tubing string into said next perforated pay zone; and then injecting sand form said coiled tubing string to from a sand plug covering said next perforated pay zone.
9. The process as set forth in claim 8 further comprising the steps of:
repeating the steps set forth in claim 8 for the remaining perforated pay zones.
repeating the steps set forth in claim 8 for the remaining perforated pay zones.
10. A process in a fracturing system for hydraulically fracturing wells having a plurality of spaced pay zones in a borehole, the system utilizing coiled tubing apparatus including a reel and an injector for inserting a coiled tubing string from the reel; said process including the steps of:
perforating said spaced pay zones with a perforating apparatus from the outermost pay zone to the innermost pay zone;
providing a pair of spaced swab cups on the coiled tubing string for positioning on opposite sides of a selected perforated pay zone;
inserting the coiled tubing string with the swab cups thereon within the borehole for positioning on opposed sides of said selected perforated pay zone; and injecting a fracturing material from the coiled tubing string within said selected perforated pay zone between said pair of swab cups, wherein the fracturing material is a viscoelastic surfactant.
perforating said spaced pay zones with a perforating apparatus from the outermost pay zone to the innermost pay zone;
providing a pair of spaced swab cups on the coiled tubing string for positioning on opposite sides of a selected perforated pay zone;
inserting the coiled tubing string with the swab cups thereon within the borehole for positioning on opposed sides of said selected perforated pay zone; and injecting a fracturing material from the coiled tubing string within said selected perforated pay zone between said pair of swab cups, wherein the fracturing material is a viscoelastic surfactant.
11. The process as set forth in claim 10 wherein:
the spaced pay zones include a plurality of vertically spaced pay zones within a vertical borehole; and the step of inserting the coiled tubing string with the swab cups thereon includes positioning said swab cups on opposed sides of an outermost pay zone for injecting the fracturing material within said outermost pay zone.
the spaced pay zones include a plurality of vertically spaced pay zones within a vertical borehole; and the step of inserting the coiled tubing string with the swab cups thereon includes positioning said swab cups on opposed sides of an outermost pay zone for injecting the fracturing material within said outermost pay zone.
12. The process as set forth in claim 11 including the steps of raising said coiled tubing string and swab cups thereon to a next pay zone after injection of said fracturing material for positioning said swab cups on opposed sides of said next pay zone; and injecting fracturing material from said coiled tubing string within said next zone.
13. The process as set forth in claim 10 wherein:
the spaced pay zones include a plurality of horizontally spaced pay zones extending from a generally horizontally extending borehole portion; and the step of inserting the coiled tubing string with the swab cups thereon includes positioning said swab cups on opposed sides of an outermost pay zone for injection of fracturing material within said outermost pay zone.
the spaced pay zones include a plurality of horizontally spaced pay zones extending from a generally horizontally extending borehole portion; and the step of inserting the coiled tubing string with the swab cups thereon includes positioning said swab cups on opposed sides of an outermost pay zone for injection of fracturing material within said outermost pay zone.
14. The process as set forth in claim 13 including the steps of pulling said coiled tubing string and swab cups thereon to a next pay zone after injection of said fracturing material for positioning said swab cups on opposed sides of said next pay zone; and injecting fracturing material from said coiled tubing string within said next pay zone.
15. The process as set forth in claim 10 wherein:
the spaced pay zones include a plurality of vertically spaced lateral wells extending from a generally vertical borehole; and the step of inserting the coiled tubing string with the swab cups thereon includes positioning said swab cups on opposed sides of a lowermost pay zone for injection of fracturing material within said lowermost pay zone.
the spaced pay zones include a plurality of vertically spaced lateral wells extending from a generally vertical borehole; and the step of inserting the coiled tubing string with the swab cups thereon includes positioning said swab cups on opposed sides of a lowermost pay zone for injection of fracturing material within said lowermost pay zone.
16. The process as set forth in claim 15 including the steps of:
pulling said coiled tubing string and swab cups thereon from the lowermost pay zone to the next adjacent pay zone, and then inserting said coiled tubing string with swab cups thereon with a next pay zone; and injecting fracturing material from said coiled tubing string within said next pay zone.
pulling said coiled tubing string and swab cups thereon from the lowermost pay zone to the next adjacent pay zone, and then inserting said coiled tubing string with swab cups thereon with a next pay zone; and injecting fracturing material from said coiled tubing string within said next pay zone.
17. A process for hydraulically fracturing a pay zone in a well having a plurality of spaced pay zones in a borehole comprising the following steps:
perforating the pay zones;
providing a coiled tubing string having a pair of spaced swab cups thereon for positioning on opposed sides of a selected pay zone;
inserting the coiled tubing string with the pair of spaced swab cups thereon within the borehole and lowering the coiled tubing string to the selected pay zone with each one of the pair of the swab cups positioned on an opposed side of the selected pay zone; and injecting a fracturing material from the coiled tubing string within the selected pay zone between the pair of swab cups, wherein the fracturing material is a viscoelastic surfactant.
perforating the pay zones;
providing a coiled tubing string having a pair of spaced swab cups thereon for positioning on opposed sides of a selected pay zone;
inserting the coiled tubing string with the pair of spaced swab cups thereon within the borehole and lowering the coiled tubing string to the selected pay zone with each one of the pair of the swab cups positioned on an opposed side of the selected pay zone; and injecting a fracturing material from the coiled tubing string within the selected pay zone between the pair of swab cups, wherein the fracturing material is a viscoelastic surfactant.
18. The process as set forth in claim 17 including the steps of:
providing a reel with coiled tubing for the coiled tubing string wound thereon;
providing a wireline for a perforating apparatus;
and perforating the pay zones with said perforating apparatus in a single pass of the perforating apparatus.
providing a reel with coiled tubing for the coiled tubing string wound thereon;
providing a wireline for a perforating apparatus;
and perforating the pay zones with said perforating apparatus in a single pass of the perforating apparatus.
19. The process as set forth in claim 17 including the steps of:
providing a pair of upper swab cups and a pair of lower swab cups on said tubing string; and lowering the coiled tubing string within the borehole to the selected pay zone with the pair of upper swab cups and the pair of lower swab cups on opposed sides of said selected pay zone.
providing a pair of upper swab cups and a pair of lower swab cups on said tubing string; and lowering the coiled tubing string within the borehole to the selected pay zone with the pair of upper swab cups and the pair of lower swab cups on opposed sides of said selected pay zone.
20. A process for perforating and fracturing a plurality of spaced pay zones in a borehole for a well; the system utilizing coiled tubing apparatus including a reel and injector for inserting a coiled tubing string from the reel within the borehole; said process comprising the following steps:
(1) perforating the plurality of pay zones from an outermost pay zone;
(2) providing a pair of swab cups on the coiled tubing string for positioning on opposed sides of the pay zones;
(3) injecting the coiled tubing string with the swab cups thereon within the borehole for lowering the coiled tubing string to the outermost perforated pay zone with the swab cups positioned on opposed sides of said outermost pay zone;
(4) injecting a fracturing material from the coiled tubing string into the outermost pay zone between the swab cups, wherein the fracturing material is a viscoelastic surfactant;
(5) raising the coiled tubing string to the next adjacent pay zone with said swab cups on opposed sides of the next pay zone; and (6) injecting the fracturing material from the coiled tubing string into a next pay zone.
(1) perforating the plurality of pay zones from an outermost pay zone;
(2) providing a pair of swab cups on the coiled tubing string for positioning on opposed sides of the pay zones;
(3) injecting the coiled tubing string with the swab cups thereon within the borehole for lowering the coiled tubing string to the outermost perforated pay zone with the swab cups positioned on opposed sides of said outermost pay zone;
(4) injecting a fracturing material from the coiled tubing string into the outermost pay zone between the swab cups, wherein the fracturing material is a viscoelastic surfactant;
(5) raising the coiled tubing string to the next adjacent pay zone with said swab cups on opposed sides of the next pay zone; and (6) injecting the fracturing material from the coiled tubing string into a next pay zone.
21. The process as set forth in claim 20 including the step of repeating steps 5 and 6 as set forth in claim 20 in sequence for any remaining pay zones.
22. The process as set forth in claim 21 including the steps of:
mounting said pair of swab cups on the coiled tubing string in a spaced relation to each other, such that said coiled tubing string can be raised in successive steps from the outermost pay zone to an innermost pay zone while maintaining the spacing between the swab cups.
mounting said pair of swab cups on the coiled tubing string in a spaced relation to each other, such that said coiled tubing string can be raised in successive steps from the outermost pay zone to an innermost pay zone while maintaining the spacing between the swab cups.
23. The process as set forth in claim 22 including the steps of:
providing a wireline for a perforating apparatus;
and perforating the pay zones in sequence from the outermost pay zone to the innermost pay zone with a single trip of the perforating apparatus.
providing a wireline for a perforating apparatus;
and perforating the pay zones in sequence from the outermost pay zone to the innermost pay zone with a single trip of the perforating apparatus.
24. A process for perforating and fracturing a plurality of vertically spaced pay zones in a shallow vertically extending gas well having a depth less than about 3,000 feet comprising the steps of:
perforating the spaced pay zones with a perforating apparatus in a single trip of the perforating apparatus within the well;
providing a coiled tubing apparatus including a reel and injector for inserting a coiled tubing string from the reel in the well;
positioning a pair of opposed spaced swab cups on the coiled tubing string for positioning on opposed sides of a selected pay zone for isolating the pay zone;
inserting the coiled tubing within the well and positioning the swab cups on opposite sides of a lowermost perforated pay zone;
injecting a fracturing material having a low friction from the coiled tubing string within the lowermost perforated pay zone;
then raising the coiled tubing string to a next superjacent perforated pay zone with the swab cups isolating the next superjacent perforated pay zone;
then injecting the fracturing material from the coiled tubing string within the next superjacent perforated pay zone; and repeating the steps of raising the coiled tubing string and injecting the fracturing material for all remaining perforated pay zones in the shallow well.
perforating the spaced pay zones with a perforating apparatus in a single trip of the perforating apparatus within the well;
providing a coiled tubing apparatus including a reel and injector for inserting a coiled tubing string from the reel in the well;
positioning a pair of opposed spaced swab cups on the coiled tubing string for positioning on opposed sides of a selected pay zone for isolating the pay zone;
inserting the coiled tubing within the well and positioning the swab cups on opposite sides of a lowermost perforated pay zone;
injecting a fracturing material having a low friction from the coiled tubing string within the lowermost perforated pay zone;
then raising the coiled tubing string to a next superjacent perforated pay zone with the swab cups isolating the next superjacent perforated pay zone;
then injecting the fracturing material from the coiled tubing string within the next superjacent perforated pay zone; and repeating the steps of raising the coiled tubing string and injecting the fracturing material for all remaining perforated pay zones in the shallow well.
25. The process for perforating and fracturing a plurality of vertically spaced pay zones as set forth in claim 24 including the step of:
positioning a plurality of upper swab cups and a plurality of lower swab cups on said coiled tubing for isolation of the pay zones when positioned in opposed sides of the pay zones.
positioning a plurality of upper swab cups and a plurality of lower swab cups on said coiled tubing for isolation of the pay zones when positioned in opposed sides of the pay zones.
26. The process for perforating and fracturing a plurality of vertically spaced pay zone as set forth in claim 24 wherein the step of injecting the fracturing material comprises injecting a viscoelastic surfactant fracturing fluid having a low friction.
27. The process of perforating and fracturing a plurality of vertically spaced pay zones as set forth in claim 24 wherein the step of injecting the fracturing material comprises injecting a fracturing fluid having a fiber-based additive to provide a low friction.
28. A process for perforating and fracturing a plurality of vertically spaced pay zones in a shallow vertically extending well having a depth less than about 3,000 feet comprising the steps of:
perforating the spaced pay zones with a perforating apparatus from an outermost pay zone to an innermost pay zone;
providing a coiled tubing apparatus including a reel and injector for inserting a coiled tubing string from the reel in the well;
positioning a packer on the coiled tubing string for positioning on the upper side of a selected pay zone for isolating the selected pay zone;
inserting the coiled tubing within the well and positioning the packer adjacent an upper side of a lowermost perforated pay zone;
injecting a fracturing material having a low friction from the coiled tubing string within the lowermost perforated pay zone;
then injecting sand from said coiled tubing string into the pay zone after injection of said fracturing material to form a sand plug covering the lowermost perforated pay zone;
then raising the coiled tubing string to a next superjacent perforated pay zone with the packer isolating the next superjacent perforated pay zone;
then injecting the fracturing material from the coiled tubing string within the next superjacent perforated pay zones;
then injecting sand from said coiled tubing string into the next superjacent pay zone to form a next sand plug covering the next superjacent perforated pay zone; and repeating the steps of raising the coiled tubing string, injecting the fracturing material, and then injecting sand for all remaining perforated pay zones in the shallow well.
perforating the spaced pay zones with a perforating apparatus from an outermost pay zone to an innermost pay zone;
providing a coiled tubing apparatus including a reel and injector for inserting a coiled tubing string from the reel in the well;
positioning a packer on the coiled tubing string for positioning on the upper side of a selected pay zone for isolating the selected pay zone;
inserting the coiled tubing within the well and positioning the packer adjacent an upper side of a lowermost perforated pay zone;
injecting a fracturing material having a low friction from the coiled tubing string within the lowermost perforated pay zone;
then injecting sand from said coiled tubing string into the pay zone after injection of said fracturing material to form a sand plug covering the lowermost perforated pay zone;
then raising the coiled tubing string to a next superjacent perforated pay zone with the packer isolating the next superjacent perforated pay zone;
then injecting the fracturing material from the coiled tubing string within the next superjacent perforated pay zones;
then injecting sand from said coiled tubing string into the next superjacent pay zone to form a next sand plug covering the next superjacent perforated pay zone; and repeating the steps of raising the coiled tubing string, injecting the fracturing material, and then injecting sand for all remaining perforated pay zones in the shallow well.
29. The process as set forth in claim 28 wherein the step of positioning the packer on the coiled tubing string comprises the positioning of a swab cup on the coiled tubing string.
30. The process as set forth in claim 28 wherein the step of positioning the packer on the coiled tubing string comprises the positioning of a mechanical packer on the coiled tubing string which is released and reset upon movement of the coiled tubing string from one pay zone to another pay zone.
31. The process for perforating and fracturing the plurality of vertically spaced pay zone as set forth in claim 28 wherein the step of injecting a fracturing material comprises injecting a viscoelastic surfactant fracturing fluid having a low friction.
32. The process of perforating and fracturing the plurality of vertically spaced pay zones as set forth in claim 28 wherein the step of injecting a fracturing material comprises injecting a fracturing fluid having a fiber-based additive to provide a low friction.
33. The process as set forth in claim 28 wherein the step of injecting a fracturing material comprises injecting a fracturing material having a friction less than about 4,650 psi/1,000 feet within coiled tubing having an outer diameter of 1 3/4 inches.
34. The process as set forth in claim 28 wherein the step of injecting a fracturing material comprises injecting a fracturing material having a friction less than 1,680 psi/1,000 feet within coiled tubing having an outer diameter of 2 3/8 feet.
35. A process for perforating and fracturing a plurality of vertically spaced pay zones in a shallow vertically extending gas well having a depth less than about 5,000 feet comprising the steps of:
perforating the spaced pay zones with a perforating apparatus;
providing a coiled tubing apparatus including a reel and an injector for inserting coiled tubing from the reel in the well;
positioning a pair of opposed spaced swab cups on the coiled tubing for positioning on opposed sides of a selected pay zone for isolating the pay zone;
inserting coiled tubing having an outer diameter of 2 3/8 inches within the well and positioning the swab cups on opposite sides of a lowermost perforated pay zone;
injecting a fracturing material having a friction less than about 1,200 psi/1,000 feet from the coiled tubing within the lowermost perforated pay zone;
then raising the coiled tubing to a next superjacent perforated pay zone with the swab cups isolating the next superjacent perforated pay zone;
then injecting the fracturing material having a friction less than about 1,200 psi/1,000 feet from the coiled tubing within the next superjacent perforated pay zone; and repeating the steps of raising the coiled tubing and injecting said fracturing material for all remaining perforated pay zones in the shallow well.
perforating the spaced pay zones with a perforating apparatus;
providing a coiled tubing apparatus including a reel and an injector for inserting coiled tubing from the reel in the well;
positioning a pair of opposed spaced swab cups on the coiled tubing for positioning on opposed sides of a selected pay zone for isolating the pay zone;
inserting coiled tubing having an outer diameter of 2 3/8 inches within the well and positioning the swab cups on opposite sides of a lowermost perforated pay zone;
injecting a fracturing material having a friction less than about 1,200 psi/1,000 feet from the coiled tubing within the lowermost perforated pay zone;
then raising the coiled tubing to a next superjacent perforated pay zone with the swab cups isolating the next superjacent perforated pay zone;
then injecting the fracturing material having a friction less than about 1,200 psi/1,000 feet from the coiled tubing within the next superjacent perforated pay zone; and repeating the steps of raising the coiled tubing and injecting said fracturing material for all remaining perforated pay zones in the shallow well.
36. The process as set forth in claim 35 including the steps of:
mounting said pair of swab cups on the coiled tubing in a spaced relation to each other at least equal to a width of a maximum pay zone so that said coiled tubing can be raised in successive steps from the lowermost pay zone to a uppermost pay zone while maintaining the spacing between the swab cups.
mounting said pair of swab cups on the coiled tubing in a spaced relation to each other at least equal to a width of a maximum pay zone so that said coiled tubing can be raised in successive steps from the lowermost pay zone to a uppermost pay zone while maintaining the spacing between the swab cups.
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|---|---|---|---|
| US10811998P | 1998-11-12 | 1998-11-12 | |
| US60/108,119 | 1998-11-12 |
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| CA2268597A1 CA2268597A1 (en) | 2000-05-12 |
| CA2268597C true CA2268597C (en) | 2006-06-20 |
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| CA002268597A Expired - Fee Related CA2268597C (en) | 1998-11-12 | 1999-04-06 | Process for hydraulically fracturing oil and gas wells utilizing coiled tubing |
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| US (1) | US6446727B1 (en) |
| CA (1) | CA2268597C (en) |
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| US5085276A (en) * | 1990-08-29 | 1992-02-04 | Chevron Research And Technology Company | Production of oil from low permeability formations by sequential steam fracturing |
| US5265678A (en) * | 1992-06-10 | 1993-11-30 | Halliburton Company | Method for creating multiple radial fractures surrounding a wellbore |
| US5287741A (en) | 1992-08-31 | 1994-02-22 | Halliburton Company | Methods of perforating and testing wells using coiled tubing |
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| US5472049A (en) * | 1994-04-20 | 1995-12-05 | Union Oil Company Of California | Hydraulic fracturing of shallow wells |
| US5417284A (en) * | 1994-06-06 | 1995-05-23 | Mobil Oil Corporation | Method for fracturing and propping a formation |
| US5551516A (en) | 1995-02-17 | 1996-09-03 | Dowell, A Division Of Schlumberger Technology Corporation | Hydraulic fracturing process and compositions |
| US5722490A (en) | 1995-12-20 | 1998-03-03 | Ely And Associates, Inc. | Method of completing and hydraulic fracturing of a well |
| US5954133A (en) * | 1996-09-12 | 1999-09-21 | Halliburton Energy Services, Inc. | Methods of completing wells utilizing wellbore equipment positioning apparatus |
| US5947200A (en) * | 1997-09-25 | 1999-09-07 | Atlantic Richfield Company | Method for fracturing different zones from a single wellbore |
| US6070666A (en) * | 1998-04-30 | 2000-06-06 | Atlantic Richfield Company | Fracturing method for horizontal wells |
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1999
- 1999-01-29 US US09/240,125 patent/US6446727B1/en not_active Expired - Lifetime
- 1999-04-06 CA CA002268597A patent/CA2268597C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| US6446727B1 (en) | 2002-09-10 |
| CA2268597A1 (en) | 2000-05-12 |
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