US3559737A - Underground fluid storage in permeable formations - Google Patents

Abstract

Fractures in caprocks of fluid storage reservoirs can be sealed and flow barriers can be established at desired regions of porous rocks by locally freezing the formation water to form an impervious cryogenic structure and/or by forming gas hydrates by contacting hydrate forming gases with formation water subjected to heat removal therefrom and agitation, for the purpose of stored fluid leakage control, increasing storage volume of limited reservoirs, and formation of storage conditions in homoclines and monoclines.

Description

United States Patent [72] Inventors James F. Ralstin; 2.991.624 7/1961 Closs et a1 61/.5 Jack H. Heathman, 672 Union Center 3,152,640 10/ 1964 Marx 166/273X Building, Wichita, Kans. 67202 3,175,614 3/1965 Wyl1ie.. 166/305X [21] Appl. No. 726,720 3,295,328 1/1967 Bishop 61/.5 [22] Fil d May 6, 1968 3,344,607 10/1967 Vignovich 611.5 [45] Patented Feb. 2, 1971 3,379,260 4/1968 166/292X 3,393,738 7/1968 166/309X 3,477,509 1 1/ 1969 l66/274X [54] UNDERGROUND FLUID STORAGE 1N PERMEABLE FORMATIONS Primary Examiner-Stephen J. Novosad 0 Claims 9 Drawing Figs. Attorney-John H. WlddOWSOn [52] U.S.Cl 166/281,

166/27 166/305 ABSTRACT: Fractures in caprocks of fluid storage reservoirs [51] Int. Cl E2lb 33/138, can besealed and n barriers can be established at desired E2lb43/26 regions of porous rocks by locally freezing the formation [50] Field of Search 166/285, water to f n i rvious cryogenic structure and/or by (305D 2715 61/5 forming gas hydrates by contacting hydrate forming gases with [56] Reerenm Cited fonnation water subjected to heat removal therefrom and agitation, for the purpose of stored fluid leakage control, in- UNITED STATES PATENTS creasing storage volume of limited reservoirs, and formation 2,777,679 1/1957 Ljungstrom l66/302X of storage conditions in homoclines and monoclines.

PATENIED FEB 2 |97l 3,559; 737 I sum 1 or 2 I7 F/GI 4 INVENTOR.

JACK H. HEATHMAN BY JAMES F. RALSTIN ATTORNEYS UNDERGROUND FLUID STORAGE IN PERMEABLE FORMATIONS This invention relates to the underground storage of fluids. In one aspect it relates to the underground storage of gaseous fluids. In another aspect it relates to a localized in situ freezing process whereby an impervious cryogenic structure is formed to seal fractures in the caprock of a permeable formation containing stored fluids. In another aspect it relates to a localized in situ freezing process whereby an impervious cryogenic structure is formed at a strategic location, to enlarge the available storage volume. In yet another aspect it relates to a method of forming a gas hydrate, in situ, in order to seal fractures in formations and the like in the caprock to prevent the undesired migration of the stored fluid out of the permeable formation. In another aspect it relates to a method of forming gas hydrates within a porous formation to enlarge the availa-' ble fluid storage volume within the porous rock.

In recent years much attention has been directed to underground storage of fluids, especially to the storage of volatile fluids such as hydrocarbon fuels. Due to the varying seasonal demands for hydrocarbon fuels much work has been done in discovering methods of storing these fuels. However, many of the prior art methods utilize methods of forming caverns and the like by mining or dissolving a cavity in a soluble strata. Such caverns are limited by size and economics.

Other prior art methods have utilized surface reservoirs wherein the fluids are stored within a vessel or reservoir having a cap or cover over the reservoir. The fluids are then maintained at a temperature sufficiently low so that the vapor pressures of the fluids will not exceed pressures which the cap cover is designed to withstand. For large volume storage such methods of utilizing surface reservoirs are undesirable due to the expense in constructing the reservoirs and the necessity of requiring a portion of the surface of the land in order to provide for such storage. Thus, means are constantly being sought whereby fluids can readily be stored in natural formations of the earth which are economical to use, and which will yield, on recapture, a desirable quantity of the product stored within the formation.

Other prior art methods have utilized underground fluid storage wherein the fluid is stored in large quantities of porous and permeable rock at various depths beneath the surface of the earth. Such underground storage is especially feasible in geographic areas having depleted or semidepleted oil and gas reservoirs which can be converted into fluid storage fields. In areas devoid of depleted or semidepleted fields, aquifer/aquiclude systems associated with structural and/or stratigraphic traps can be converted to fluid storage reservoirs. These systems are called aquifer storage facilities.

In the utilization of the underground storage facilities leakage from the storage reservoirs to higher porous and permeable rock beds frequently occurs through fractures or breaks in the caprock, through nonsealing faults, and the like. Sometimes it is feasible to collect leaking fluids from wells completed in the higher rock beds and cycle the fluids back to the storage formation. However, leakage control by fluid cycling is an economic burden on the operation. Thus, other methods of fluid leakage control are highly desirable.

Several methods for soil and porous rock impermeation are known in the prior art wherein grout is employed to seal the fracture or break in the caprock. However, the success of the grouting depends on the complete invasion of the grout into the fracture channels, pores, and pore channels of the rock body which is to be impermeated. Due to the very nature of the rock structure a complete invasion of the leakage channel by the grout is frequently not achieved. Thus, the prior art methods which employ the grouting technique many times are undesirable.

Even when a desirable fluid storage reservoir is located having an anticlinal trap surrounded by structural conditions suitable for fluid storage, the reservoir is frequently limited in storage capacity by a saddle region or spill point. The capacity of such a reservoir can be increased if gas migration beyond the saddle region is prevented by regional impermeation of the storage formation.

Further, frequently structural conditions favorable to fluid storage cannot be found near population centers, even though various porous and permeable rocks overlain by impervious formations are encountered below the ground. Thus, it is very desirable to provide a means to modify the underground structural conditions so that a reservoir is formed which can be utilized for the underground storage of fluids thus providing a supply source near the population centers. Thus, it is highly desirable to provide a method wherein the structurally high end of the porous rock bed, the outcropping end, can be impermeated thus producing a desirable reservoir for the underground storage of the fluid.

According to the present invention, a method is provided for impenneating an underground formation for sealing fractures in the porous rock and/or its caprock, by removing heat from the rocks and the saturating water, thus causing the water to crystallize and form a substantially impervious cryogenic structure.

Further according to the invention, a method of rock impermeation and channel sealing is provided whereby the formation water is cooled and contacted with a gas capable of forming gas hydrates so that a substantially impervious rock hydrate structure is formed thereby.

Further, a method is provided for sealing fractures and/or broken formations in the upper impervious caprock covering a porous geological structure by removing heat from the aquifer and/or aquiclude water and thus producing localized cooling of the same so that an impervious structure is formed which seals the broken or fractured caprock structure.

Further according to the invention, a method is provided wherein localized cooling of aquifer water is employed to form gas hydrates in the rock pore spaces in order to employ the hydrates so formed to seal the broken and/or cracked formations within the caprock covering the desired storage area.

Further, according to the invention, a method is provided wherein the heat flow through porous rocks and saturating fluids is employed to initiate and maintain localized in situ freezing so that the aquifer and/or aquiclude water is crystal lized and an impervious cryogenic structure is formed.

Further according to the invention, a method is provided whereby the fluid storage capacity of the structure can be increased by means of initiating and maintaining a localized in situ freezing process whereby the water in the aquifer and/or aquiclude is crystallized and an impervious cryogenic structure similar to a dam is formed across the saddle region of the structure.

Drawings accompany and are a part of this disclosure. These drawings depict preferred specific embodiments of the underground storage in permeable formations of the invention, and it is to be understood that these drawings are not to unduly limit the scope of the invention. In the drawings,

FIG. I is a plan view of a portion of the ground surface intended to illustrate the manner in setting out a method of this invention in preparing for the construction of a flow barrier in a porous and permeable formation or to repair fractures or breaks in its caprock;

FIG. 2 is a cross section of the surface of the earth taken along the line 2-2 of FIG. 1 illustrating the application of the method of this invention to form a flow barrier to enlarge the fluid storage area of an underground structure and to seal fractures or breaks in the caprock above the formation being employed for fluid storage;

FIG. 3 is a cross section taken along the line 3-3 of FIG. 1 illustrating the formation of a barrier according to the present invention;

FIG. 4 is a cross section taken along the lines 4-4 of FIG. 1 illustrating the sealing of a fracture system in the caprock and the like above the formation being employed for fluid storage;

FIG. 5 is a cross-sectional view of the earth depicting a typical homocline showingthe formation of storage conditions by local impermeation methods of the present invention;

FIG. 6 is a cross section of the earth of a typical anticline showing the use of directionally drilled wells for in situ formation freezing and/or for forming a hydrate according to the present invention;

FIG. 7 is a structural contour map of a typical anticline showing the placement of gas hydrate flow barriers to seal fractures in a caprock and to enlarge a reservoir by the formation of a damlikc barrier in the storage formation;

FIG. 8 is a schematic cross-sectional view illustrating a heat sink well means employed by the process of the present invention;

FIG. 9 is a schematic cross-sectional view of a refrigerant circulation system used according to the process of the present invention.

In the following is a discussion and description of the invention made with reference to the drawings whereupon the same reference numerals are used to indicate the same or similar parts and/or structure.

The discussion and description is of preferred specific embodiments of the new process of our invention for forming formations of our invention for storing fluids underground, and it is to be understood that the discussion and description is not to unduly limit the scope of the invention.

Referring now to FIG. 1, a plan view of a portion of the ground is illustrated having contour lines 11 which indicate a saddle region 12 across which a barrier structure, 14, is to be constructed and a crest region 16 which has a fracture system or breaks therein which is to be sealed by local impermeation 17. In preparation for building barrier 14 in saddle region 12 the present method can be applied by drilling and completing a series of wells 18 at suitable intervals so that wells 18 form a line which transverses the saddle region 12. The bottom portion of wells 18 are positioned within the aquifer zone which will be discussed in detail hereinafter. Likewise, in preparation for the forming of impervious structure 17 to seal the fractures or breaks in the caprock covering the crest of the anticline 16 the present method may be applied by drilling and completing a series of wells 19 at suitable intervals so that wells 19 fonn a line which approximately follows the system of the fractures or breaks in the caprock. The bottom portion of wells 19 are positioned in the caprock in the immediate vicinity of the fractures or breaks in the caprock as will be discussed hereinafter.

Referring now to FIG. 2 a cross-sectional view of the ground taken in lines 2-2 of FIG. 1 is illustrated. Underground structure or formation 21 is shown comprising an aquifer zone 22, such as sandstone, having an aquiclude zone 23, or a caprock zone, such as limestone, positioned on top of aquifer zone 22. Likewise, a sufiiciently impervious lower layer aquiclude zone 24, such as dolomite, is positioned below aquifer zone 22. Aquifer zone 22 is the prospective fluid storage formation. However, it should be understood that other types of impervious substances can make up the impervious zones which are positioned above and below aquifer zone 22. Other types of impervious materials which can serve as the caprock which covers the prospective storage formation are well known in the field of geology.

An aquifer as used herein is defined as a water-bearing bed of stratum of underground porous and permeable rock, sand, or gravel. In order for the formation to serve as a reservoir for fluid storage use, such as gas storage, the aquifer must be over- Iayed by beds of a sufficiently impervious aquiclude or caprock through which stored fluids cannot escape.

Referring now to FIG. 2 in conjunction with FIG. I, aquifer zone 22 is overlain by impervious aquiclude zone 23 and underlain by impervious aquiclude zone 24 and is associated with a doubly-plunging asymmetrical anticline. The anticline considered for fluid storage joins a larger anticlinal structure through saddle region 12. However, the anticline has a limited storage capacity because its structural closure is limited by saddle region 12. Further, aquiclude zone 23 has a localized fracture system 26 near its crest, and thus allows fluids stored therein to readily escape and as such is highly undesirable. Fracture system 26 near the crest of aquiclude zone 23 can be discovered by geophysical and/or nonsteady water pumping tests, tracer surveys, and the like which are well known. Once fracture system 26 in aquiclude zone 23 is discovered fracture system 26 must be sealed if the reservoir is to be utilized for fluid storage in aquifer zone 22. Likewise. it is desirable to form an impervious structure, such as barrier 14, across saddle region 12 to prevent the movement of stored fluids from passing beyond the saddle region of the formation and thus increase the storage capacity of aquifer zone 12. Thus, by the method of the present invention of utilizing in situ freezing to crystallize the aquiclude water to seal the flow channels of fracture system 26, fluids stored within aquifer zone '22 are prevented from escaping through the fracture system. Likewise, by crystallizing aquifer water within saddle region 12 an impervious wall structure, such as barrier 14, is formed and the movement of storedfluids is restricted thus enlarging the capacity of aquifer zone 22 so that a larger volume can be utilized for the storage of fluids therein. 7

Referring now to FIG. 3 in conjunction with FIG. 2 the method of forming the barrier 14, across saddle region 12 of underground formation 22 will be discussed. A plurality of wells 18 are completed in aquifer zone 22 and used as lower temperature heat sinks relative to the surroundings in order to crystallize aquifer water and form a cryogenic structure 14 in aquifer zone 22 up to the desired distance away from each of wells 18. Such can be accomplished by pumping a coolant, such as a refrigerant, down to the bottom of wells 18 by pump units 27. As is readily apparent, the barrier 14 is constructed by in situ crystallizing of the aquifer water in aquifer zone 22. Cryogenic rock-water structure 14 prevents fluid migration beyond saddle region 12 and thus increases the storage capacity of aquifer zone 22 by lowering the extreme spill point of the formation. Thus, it is readily apparent that without the use of cryogenic barrier 14 fluid storage in aquifer zone 22 is confined, as viewed from the top, within contour lines 260 (see FIG. 1) wherein contour line 260 denotes points on the top of aquifer zone 22 equidistant and vertically from a reference plane, such as sea level, measured in feet. However, with the formation of cryogenic barrier 14 the capacity of formation 22 is increased by extending the gas-water interface to contour line 300. Thus, by employing the method of forming an in situ cryogenic barrier across the saddle region of the formation the total fluid storage capacity of the aquifer zone is greatly enlarged.

Referring now to FIG. 4, in conjunction with FIG. 2, the method of sealing fracture system 26 in aquiclude zone 23 will be discussed. A plurality of wells 19 are completed in aquiclude zone 23 which overlays aquifer zone 22 which is to be utilized for fluid storage, such as natural gas storage. When fracture system 26 is found to be present in aquiclude zone 23, and it is desired to utilize aquifer zone 22 for natural gas or other fluid storage, fracture system 26 must be sealed. Wells 19 are set a desired distance apart and are positioned so as to substantially follow the line of fracture system 26. When wells 19 are completed a coolant, such as a refrigerant, is pumped down the wells by pump units 27. The refrigerant cools the formation and the aquifer and aquiclude water is frozen in situ thus fonning a cryogenic structure 17 which seals fracture system 26 and thus prevents the stored fluids from escaping aquifer zone 22 through fracture system 26.

Referring now to FIG. 5, structural formation 29 which can be modified by the present invention and thus made into a suitable fluid storage reservoir is illustrated. In this situation the present invention involves the establishment of favorable storage conditions in porous, permeable formation 31 of a homocline or monocline in which successively younger rock strata dip away from a central uplift, and in the case of a homocline are gently curved in a direction perpendicular to the direction of the dip. When such a formation as formation 29 is overlain by a successively impervious formation 32, a cryogenic structure 14can be developed in permeable formation 31 by completing a plurality of heat sink wells 18 at a desired vertical distance from the surface of the ground so that a refrigerant can be pumped into wells 18 by pump unit 27 and thus cool the formation and crystallize the water to seal the outcropping or upper end of permeable fonnation 31. Depending upon the degree of dip, the thickness of permeable formation, and the fluid storage capacity desired it may be desirable and necessary to locate geological conditions where the permeable bed is also underlain by an impervious formation, such as formation 33.

Referring now to FIG. 8, a schematic of the proposed heat sink wells 18 and I9 employed according to the present invention are shown. A suitable refrigeration system. such as a vapor compression refrigeration system, can be used to pump an appropriate refrigerant such as a freon. CO liquified petroleum gas (LPG), and the like, down an insulated tubing 34, to produce a cooling effect to freeze the water of the aquifer surrounding the well bore. When the refrigerant reaches the last joint of tubing 34 it is throttled by a throttle means 36, so that some of the refrigerant flushes into vapor during the throttling process. The remainder of the refrigerant evaporates inside the bottom section of casing 37 by extracting heat from the rock matrix and water or ice in the pore spaces, and the evaporated refrigerant flows up through the annulus between insulated tubing 34 and of the insulated long string casing 37, and enters compressor 38 as a saturated or superheated vapor at low pressure. Following compression it rejects heat in a condenser and begins its cycle down tubing 34 again. The string of casing 37 is preferably thermally insulated from the formations above the storage formation by an insulation material, such as an organic or inorganic liquid, and the insulation material is placed between the long string of casing 37 and short strings of outer casing 39 above packer 41 but below Christmas tree 42. Low temperature resistant high strength cement 43 is employed to bind the casing strings to the fonnation through the caprock and the storage zone. The annular space between the overlying beds and the outer casing string is filled with casing pack material 44 which are well known in the drilling art and as such are believed sufficiently well known. Surface conductor casing 46 is cemented with low temperatures being considered. In some areas intermediate strings of casings may be necessary and in others it may be possible to eliminate the outer string of easing completely and insulate only the long string of easing from formation by using low conductivity casing packs above the cement top. However, such will vary widely depending upon the area wherein the formation is located, the depth of the formation, and the type of the formation.

The spacing and the number of wells 18 and 19, the refrigerant type and circulation rates, the duration of time for the propagation of approximately egg-shaped water crystallizationand final merging into an impervious cryogenic rockwater structure, depend upon a multitude of factors, such as chemical, mechanical, thermoproperties of the formation, and the in situ water, structural conditions, formation temperature, formation pressure, and the like. Obviously, the method of porous rock freezing requires close welded spacing, such as measured in tens of feet.

Referring now to FIG. 6 a plurality of wells 47 are illustrated which have been drilled by a directional drilling process in order to provide greater contact area between the formation of interest and heat sink wells 47. However, the use of directionally drilled wells 47 will depend upon the depth of the formation and its structural attitude. Thus, the decision to employ direction drilling in order to provide heat sink wells would depend on the circumstances throughout the reservoir being prepared.

Referring now to FIG. 9 a refrigerant circulation system for forming a cryogenic structure according to the present invention is depicted when it is desirable to employ wider well spacing. A line of refrigerant injection wells 48 and withdrawal wells 49 are drilled into the aquifer or aquiclude zone where the water-rock system is to be locally frozen. Injection wells 48 and withdrawal wells 49 are cased through the formation of interest and perforated selectively at a level corresponding to an approximately half way point between the top and the bottom of the cryogenic structure to be fonned. By this limited entry perforation technique, selective fracturing at each well, designated by numeral 51, flow channels 52 of least resistance are established between any pair of injection wells 48 and withdrawal wells 49. The liquid refrigerant is pumped by pump 53 through conduit 54 into tubing 56 of injection wells 48 and withdrawn by submergible pumps 57 located in each withdrawal well 49 together with formation water. The liquid refrigerant and the formation water is then pumped up tubing 58 and through conduit 59 and into pump means 53. The cycling of refrigerant through the formation between the wells is first carried on without cooling and heat rejection at the surface. The purpose of first cycling the refrigerant through the formation without cooling is to saturate flow channels 52 formed by hydraulic fracturing of the rock matrix immediately surrounding the flow channels with refrigerant. During the refrigerant circulation process at normal temperatures the water cut of the refrigerant withdrawn from the formation will steadily decline to a negligible level or it will stabilize. Water is removed at the surface by separators, (not shown), and the separated refrigerant is sent to a condenser to begin another cycle. When the water cut stabilizes at a low value, the refrigerant is gradually cooled at pump 53. The refrigerant picks up heat from high temperature heat sources, i.e., the for mation rock matrix and water, while it flows through the channels of the formation, and it rejects heat at the low temperature heat sink, the surface separation and refrigeration systems. A refrigeration plant such as a vapor pressure refrigeration plant can be employed to cool the refrigerant circulating through the formation.

When the temperature of the refrigerant in the flow channels is reduced below the freezing point of the formation water, the cryogenic structure begins to form, and the interface between the ice region and the cold water region propagates away from the flow channels. Since the refrigerant saturates the flow channels but does not freeze at the operating pressure and temperature of the system, it continues to circulate between pairs of wells, such as injection wells 48 and withdraw wells 49. Thus, the refrigerant acts as a low temperature heat sink relative to the formation.

The refrigerant employed by the above-mentioned process can be any suitable refrigerant which is known in the art. However, it is preferred that the refrigerant selected be water immiscible having a density equal to or slightly less than the density of the formation water and a viscosity higher than the viscosity of the formationwater. Further, the refrigerant should be in the liquid phase during its injection into the wells and its flow through the formation and have high heat conductivity. The requirement of the viscosity of the refrigerant being higher than the viscosity of the formation water is a compromise between minimization of viscous fingering and high pumping costs required to deliver the refrigerant to the bottom of the input wells and thus into the formation. The method of utilizing a series of refrigerant injection wells and refrigerant withdrawal wells has a definite advantage over the before-mentioned heat sink well method, wherever applicable, in that the utilization of the refrigeration injection wells and withdrawal wells provide greater area of exposure between the heat source and the heat sink, and utilizes both conduction and convection heat transfer principles.

Refrigerant injection wells 48 are equipped with insulated tubing 56 and are isolated thermally from the main body of casing 61 by an organic or inorganic insulating material which is placed in the annulus above the casing to tubing packer 62. Casing 61 is cemented 63 up to a desired point above the caprock, and the formation to casing annulus above the cement top is filled with casing-pack material of low heat conductivity 64. The surface conductor casing and the intermediate strings of casing are not shown for the sake of simplicity but are well known in the drilling art.

Refrigerant withdrawal wells 49 are also equipped with the insulation lined tubing 58, submergible pumps 57, well control equipment 66, and surface flow lines or conduits 59. Refrigerant withdrawal wells 49 can be completed with one string of casing 67 cemented to the storage formation and the aquifer zone and isolated from other formations by insulating casing-pack 68. Likewise, a construction similar to the heat sink wells shown in FlG. 8 can be used for increased protection from the possibility of leakage of the circulating fluids and for providing better thermal insulation from the strata above the storage formation and its caprock. lnterrnediatc and surface conductor casing strings are likewise not shown for the sake of simplicity.

Following the stabilization of the water out and the freezing of the water surrounding the refrigerant flow paths in the formation, one may remove the submergiblc pumps from the withdrawal wells, and thus rely on the surface pumps, to circulate the refrigerant at sufficient flow rate in order to maintain the cryogenic rock structure so formed within the boundaries determined by design and subsurface conditions.

Referring now to FIG. 7, another embodiment of the present invention will be discussed which also employs the removal of heat from the formation and the formation water surrounding the area wherein the in situ formed barrier is to be constructed in order to seal a fracture in the caprock or enlarge the total area which can be employed for storage of fluids by the continuation of a barrier in the saddle region of the formation as previously discussed with reference to FlGS. 1 and 2. Certain gases such as C0,, H28, 80 and natural and manufactured gases consisting chiefly of light parafinic hydrocarbons form solid gas hydrates when the gases come into contact with water in sufficient amounts when certain conditions as to temperature and pressure exist. It is known that the gas hydrates are formed at temperatures above the freezing temperature of the water.

Hydrocarbon hydrates are solid solutions of the hydrates of lower hydrocarbons which are capable of forming hydrates. High velocity, turbulance, pressure pulsations additives such as alcohol or acetic acid, and inoculation of small hydrate crystals accelerates the hydrate formation. It has also been found that the formation of gas hydrates with ice proceeds at a negligible rate.

A local gas hydrate barrier to fluid flow can be developed in porous and permeable bodies suitable for fluid storage by bringing low temperature water into contact with a hydrate forming gas, under favorable temperature, pressure and agitation conditions. For example, the technique of impenneation by gas hydrate 71 can be used to seal fracture system 26 in caprock 23 of underground stnicture 21 shown in FIGS. 2 and 7, to form barrier 14 at anticline saddle region 12, of aquifer zone 22. Likewise, gas hydrate 71 can be utilized to form the flow barrier in porous beds on a homocline or monocline (see FIG. 5). If the local impermeation is not necessary until the stored gas approaches the zone of leakage or spill, the gas front can be brought into contact with a cold water zone maintained by circulating chilled water between pairs of injection and withdrawal wells 48 and 49, respectively, so that hydrates are formed in situ.

If the stored gas is one which does not form gas hydrates, or if the local impermeation is to accomplished before the stored gas approaches the leakage or spill zone, other gas, such as CO, or light hydrocarbons can be injected into the formation through additional injection wells to provide hydrate forming gas. These gas injection wells are located between the approaching front of the stored gas and the line of cold water circulation wells 48 and 49.

Injection wells 48 and withdrawal wells 49 for cold water circulation can be similar to the refrigerant cycling system depicted in FIG. 9 with the exception that the circulating refrigerant is the formation water chilled at the surface and hydraulic fracturing of the formation between the wells may or may not be necessary. The circulation of the water at high rates between the wells is for the purpose for creating agitation in the formation in addition to the local cooling of the porous rocks and the contents of its pores. Thus, by the cooling effect so created, coupled with the agitation in the formation the gas hydrates of the gas are formed. The steam-jet refrigeration techniques are especially suitable to chill the water at the surface facilities.

Thus, it is readily apparent that by utilizing the method of the present invention of porous media impermeation by in situ freezing of native or added water, and by gas hydrate formation desirable results can be obtained wherein underground storage of fluids can be achieved in prospective storage reservoirs with locally'fractured caprocks and/or limited by saddle regions. Likewise, the method for sealing fractures and forming the barrier structure of the invention is by no means limited to the control of leakage or spill conditions in gas storage reservoirs. Rather, the method can be utilized whenever and wherever porous and impermeable rocks are to be locally impermeated to fluid flow and the economics and technical feasibility of the application is ascertained.

Thus, the foregoing discussion and description is made in connection with preferred specific embodiments of the method of underground storage in porous media of the invention. However, it is to be understood that the discussion and description is only intended to illustrate and teach those skilled in the art how to practice the invention and such is not to unduly limit the scope of the invention which is defined in the claims set forth hereinafter.

We claim:

1. A method for locally impermeating a naturally occurring underground formation to be used for gaseous fluid storage having a porous, permeable aquifer zone overlain by an impervious aquiclude zone having a fracture therein or having an escape path thereunder making such unsuitable for fluid storage, so that said aquifer zone can be utilized for storage of fluids without said fluids escaping from said aquifer zone comprising, subjecting said formation to a coolant in the region of said fracture or escape path as the case may be, thereby removing heat from said fonnation and fonning a barrier structure adjacent the area of said formation where said formation is subjected to the flow of said coolant, thereby providing a gaseous fluid storage reservoir.

2. The method according to claim 1 wherein said coolant is a refrigerant which is substantially water immiscible, has a density equal to or less than the density of water in said formation, has a viscosity higher than the viscosity of said water in said formation, is present in a liquid phase during injection into said fonnation, and possesses a high heat conductivity.

3. The method according to claim 2 wherein said aquifer zone is subjected to said refrigerant and said refrigerant is selected from the group consisting of carbon dioxide, freon, and the like, said refrigerant being continuously circulated down to said formation and back to the surface, and said barrier is a cryogenic structure formed in the area where said refrigerant is contacted with water in said aquifer zone.

4. The method according to claim 2 wherein said coolant is directly contacted with said formation.

5. A method for locally permeating an underground formation to be used for fluid storage having a porous, permeable aquifer zone overlain by an impervious aquiclude zone having a fracture and water therein so that said aquifer zone can be utilized for storage of fluids without said fluids escaping from said aquifer zone comprising, subjecting said aquiclude zone to a refrigerant which is substantially water immiscible, has a density equal to or less than the density of the water in said formation, has a viscosity higher than the viscosity of said water in said formation, is present in a liquid phase during injection into said formation, and possesses a high heat conductivity selected from the group consisting of carbon dioxide, freon, and the like, thereby removing heat from said formation and forming a barrier structure, said barrier being an impervious structure formed where said refrigerant is contacted with said water in said aquiclude zone thus sealing said fracture in said aquiclude zone.

6. A method for locally impermeating an underground formation to be used for fluid storage having a porous, permeable aquifer zone overlain by an impervious aquiclude zone so that said aquifer zone can be utilized for storage of fluids without said fluids escaping from said aquifer zone comprising, selectively hydraulically fracturing said formation to establish flow channels of least resistance in said formation. subjecting said formation to a coolant thereby removing heat from said formation and forming a barrier structure adjacent the area of said formation where said formation is subjected to the flow of said coolant. V

7. A method for locally impermeating an underground formation to be used for storing hydrate forming gases having a porous, permeable aquifer zone overlain by an impervious aquiclude zone so that said aquifer zone can be utilized for storage of fluids without said fluids escaping from said aquifer zone comprising, subjecting said formation to cooled water, said water being contacted and admixed with said hydrate forming gases, thereby removing heat from said formation and fonning a gas hydrate barrier structure adjacent the area where said formation is subjected to the flow of said water.

8. The method according to claim 7 which includes the step of injecting a hydrate forming gas selected from the group consisting of carbon dioxide, hydrogen sulfide. sulfer dioxide, natural and manufactured gases having a high content of light parafinic hydrocarbons. and the like, prior to the injection of said fluid to be stored in said formation, admixing said gas hydrate forming gas and said cooled water thus forming a gas hydrate barrier structure.

9. The method according to claim 8 which includes admixing an additive selected from the group consisting of alcohols, acetic acid, and the like to said hydrate forming gas to accelerate hydrate formation in said formation.

10. The method according to claim 9 wherein said cooled water is continuously circulated down to said formation and back to the surface thus maintaining cooled water within the formation at all times.

Claims (9)

1. 2. The method according to claim 1 wherein said coolant is a refrigerant which is substantially water immiscible, has a density equal to or less than the density of water in said formation, has a viscosity higher than the viscosity of said water in said formation, is present in a liquid phase during injection into said formation, and possesses a high heat conductivity.
2. 3. The method according to claim 2 wherein said aquifer zone is subjected to said refrigerant and said refrigerant is selected from the group consisting of carbon dioxide, freon, and the like, said refrigerant being continuously circulated down to said formation and back to the surface, and said barrier is a cryogenic structure formed in the area where said refrigerant is contacted with water in said aquifer zone.
3. 4. The method according to claim 2 wherein said coolant is directly contacted with said formation.
4. 5. A method for locally permeating an underground formation to be used for fluid storage having a porous, permeable aquifer zone overlain by an impervious aquiclude zone having a fracture and water therein so that said aquifer zone can be utilized for storage of fluids without said fluids escaping from said aquifer zone comprising, subjecting said aquiclude zone to a refrigerant which is substantially water immiscible, has a density equal to or less than the density of the water in said formation, has a viscosity higher than the viscosity of said water in said formation, is present in a liquid phase during injection into said formation, and possesses a high heat conductivity selected from the group consisting of carbon dioxide, freon, and the like, thereby removing heat from said formation and forming a barrier structure, said barrier being an impervious structure formed where said refrigerant is contacted with said water in said aquiclude zone thus sealing said fracture in said aquiclude zone.
5. 6. A method for locally impermeating an underground formation to be used for fluid storage having a porous, permeable aquifer zone overlain by an impervious aquiclude zone so that said aquifer zone can be utilized for storage of fluids without said fluids escaping from said aquifer zone comprising, selectively hydraulically fracturing said formation to establish flow channels of least resistance in said formation, subjecting said formation to a coolant thereby removing heat from said formation and forming a barrier structure adjacent the area of said formation where said formation is subjected to the flow of said coolant.
6. 7. A method for locally impermeating an underground formation to be used for storing hydrate forming gases having a porous, permeable aquifer zone overlain by an impervious aquiclude zone so that said aquifer zone can be utilized for storage of fluids without said fluids escaping from said aquifer zone comprising, subjecting said formation to cooled water, said water being contacted and admixed with said hydrate forming gases, thereby removing heat from said formation and forming a gas hydrate barrier structure adjacent the area where said formation is subjected to the flow of said water.
7. 8. The method according to claim 7 which includes the step of injecting a hydrate forming gas selected from the group consisting of carbon dioxide, hydrogen sulfide, sulfer dioxide, natural and manufactured gases having a high content of light parafinic hydrocarbons, and the like, prior to the injection of said fluid to be stored in said formation, admixing said gas hydrate forming gas and said cooled water thus forming a gas hydrate barrier structure.
8. 9. The method according to claim 8 which includes admixing an additive selected from the group consisting of alcohols, acetic acid, and the like to said hydrate forming gas to accelerate hydrate formation in said formation.
9. 10. The method according to claim 9 wherein said cooled water is continuously circulated down to said formation and back to the surface thus maintaining cooled water within the formation at all times.

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