US3757862A

US3757862A - Multilayer propping of fractures

Info

Publication number: US3757862A
Application number: US00279879A
Authority: US
Inventors: L Kern; F Martin
Original assignee: Atlantic Richfield Co
Current assignee: Atlantic Richfield Co
Priority date: 1972-08-11
Filing date: 1972-08-11
Publication date: 1973-09-11
Anticipated expiration: 1990-09-11

Abstract

A method for increasing the permeability of a formation whereby alternate layers of substantially insoluble particles (propping agent) and essentially soluble particles are emplaced in a fracture in said formation. At least one of the layers of substantially insoluble particles is treated with a stabilizing resin which can be hardened or otherwise set up to physically stabilize that layer to resist movement of the insoluble particles back toward the wellbore during the production of fluid through the fracture and into the wellbore.

Description

United States Patent 1191 Kern et al.

1451 Sept. 11, 1973 MULTILAYER PROPPING OF FRACTURES [75] Inventors: Loyd R. Kern; Ferman G. Martin,

both of Irving, Tex.

22 Filed: 'Au .1'1,1972

211 App]. No; 279,879

[52] US. Cl 166/280, 166/281, 166/295 [51] Int. Cl. E2lb 33/138, E2lb 43/26 [58] Field of Search 166/280, 276, 295, 166/308, 281

[56] References Cited UNITED STATES PATENTS 2,823,753 2/1958 Henderson et a1 166/276 X 2,981,334 4/1961 Powell, Jr. 166/276 2,986,538 5/1961 Nesbitt et al. 166/295 X 3,123,137 3/1964 Young et al. 166/295 3,127,937 4/1964 McGuire, Jr. et al. 166/281 X 3,155,159 11/1964 McGuire, Jr. et al. 166/280 3,235,007 2/1966 Kern et al. 166/280 3,285,339 11/1966 Walther et al. 166/295 3,297,086 l/l967 Spain 166/295 3,443,637 7 5/1969 Sparlin et al 166/295 Primary Examiner-Stephen J. Novosad AtzorneyRoderick W. MacDonald et al.

[5 7] ABSTRACT A method for increasing the permeability of a formation'whereby alternate layers of substantially insoluble particles (propping agent) and essentially soluble particles are emplaced in a fracture in said formation. .At least one of the layers of substantially insoluble particles is treated with a stabilizing resin which can be hardened or otherwise set up to physically stabilize that layer to resist movement of the insoluble particles back toward the wellbore during the production of fluid through the fracture and into the wellbore.

20 Claims, No Drawings Heretofore, it has been taught to employ in an'upright or otherwise vertically oriented fracture in a sub surface formation of the earth, alternate layers of substantially insoluble and essentially soluble particles after which the layer or layers of soluble particles are dissolved by the passage of a solvent through the fracture. This leaves a fracture which is propped open by a plurality of substantially horizontally disposed bridges of insoluble material, the bridges having void spaces therebetween where the soluble material once existed. This process is fully and completely disclosed in US. Pat. No. 3,235,007, the disclosure of which is incorporated herein by reference.

As taught in the above-cited patent, the alternate layers of soluble and insoluble particles can be deposited in the fracture either by flotation or by gravity settling or both, these processes being fully and completely dis closed in US. Pat. Nos. 3,155,159 and 3,127,937, the disclosures of which are incorporated herein by reference.

It has been found that in some cases, even though the remaining insoluble layers are under substantial .compressive force acting substantially perpendicular to the plane of the fracture, such force being sufficient to close the fracture but for the presence of the insoluble layers, a substantial amount of the insoluble particles can be washed from the fracture into the wellbore by DETAILED DESCRIPTION OF THE INVENTION By this invention, a fracture is initiatedoutwardly from a wellbore into a formation in the conventional manner by introducing a fracturing fluid into the wellbore and increasing the pressure on said fracturing fluid until a crack in the formation is formed and widened to the desired width. While the fracture is main-'- tained in its open position by the pressurized fracturing fluid, propping agent is introduced thereinto so that thereafter when the pressure on the fracturing fluid is reduced the naturally-occurring forces in the formation subsequent normal production of fluid from the formation through the fracture and into the wellbore. This is undesirable because substantial amounts of these insoluble particles can be deposited in the wellbore and/or find their way into downhole tools andequipment and cause problems or even breakdown in the operation of these tools and equipment.

SUMMARY OF TI-IE INVENTION According to this invention, there is provided a method whereby the alternate layers of soluble and insoluble particles are emplaced in a substantially upright fracture which extends from a wellbore into a subsurface earth formation and one or more of the insoluble particle layers is treated with astabilizing resin which can be set up'after emplacement of the insoluble particles in the fracture. The stabilizing resin is set up to physically stabilize the treated insoluble particle layer to resist movement of the insoluble particles of that layer towardth e wellbore during subsequent production of fluid through the fracture into the wellbore.

Accordingly, it'is an object of this invention to provide a new and improved fracturing method. It is another object to provide new and improved method for increasing the permeability of a subsurface earth formation to fluid. It is another object to provide anew and improved method for establishing high conductivity fractures in a subsurface earth formation. It is another object to provide a new and improved method for establishing a propped fracture wherein the propping agent in the fracture has at least one open channel therethrough, the propping agent in the fracture resisting movement from said fracture into the wellbore.

Other aspects, objects and advantages of this invention will be apparent to those skilled in the art-from this disclosureand the appended claims.

once again become paramount and, but for the propping agent, would force the fracture completely closed. The propping agent in the fracture thus prevents complete closing thereof and thereby maintains the permeability achieved in the first place by the fracturing process. This invention applies to any conventional processing technique. The process can use as a carrier fluid for the propping agents an aqueous base liquid or an oil base liquid. The fracturing fluid can also contain any conventional material for fracturing fluidssuch as viscosity, thickening, or gelling agents and the like.

As noted hereinabove, this invention employs the technique of US. Pat. No. 3,235,007 in the emplacement in the fracture of alternate layers of soluble and either a fluid which will normally be produced from the formation through the fracture to the wellbore or which can be introduced into the fracture from the earths surface by way of the wellbore so long as substantial dissolution of the soluble particles in the fracture is obtained. Thus, the soluble particles could be soluble in hydrocarbonaceous materials or in aqueous materials depending upon the composition of the fluids that are normally produced from the particular well and upon the desired composition for the fracturing fluid. Suitable soluble and insoluble materials are fully and completely disclosed in US. Pat. No. 3,235,007. One or more types of insoluble particles can be used in any given layer. The same is true for any given soluble layer.

In this invention, for example, a first layer of insoluble particles is laid down in the fracture after which the next adjacent layer to said first layer will be soluble particles. Thereafter, the next adjacentor third layer will be a layer of insoluble particles after which the next adjacent or fourth layer will be of soluble particles and so on as desired. The minimum requirement is two layers of insoluble particles spaced apart by an intermediate layer of soluble particles, there being no maximum number of alternating layers except that which is dic-,

'tated by the physical size of the fracture itself.

According to this invention, at least one of the layers of insoluble particles in the fracture is'treated with a V stabilizing resin. The treatment of a. particular layer of insoluble particles can take place after the soluble and insoluble layers have been emplaced and the soluble layers dissolved. A more useful technique is to first mix lizing resin with the insoluble particles absent the carrier fluid. By the prior mixing approach, the resin and insoluble particles travel down the wellbore and into the fracture together, the resin and insoluble particles being intimately mixed with one another before and/or during their travel together. The mixture is then emplaced in the fracture. In this way, a good intimate mixture of particles and resin is achieved and the next slug of carrier fluid containing soluble particles for the next adjacent layer can follow up the first slug with substantially no lost time. Catalyst can also be mixed with the resin and insoluble particles on the earths surface and then introduced into the fracture. The setting of the resin can then be triggered by heating, e.g., geothermal. heating.

it can be desirable, especially when mixing resin and insoluble particles together on the earths surface, to incorporate in any mixture of resin and insoluble particles an effective amount of at least one coupling agent which strengthens the bond between the resin and insoluble particles and/or makes the insoluble particles resin wet. Suitable coupling agents are known in the art and are fully and completely disclosed in U.S. Pat. Nos. 3,282,338; 3,297,086; 3,404,735; and 3,443,386, the disclosures of which are incorporated herein by reference.

A particularly desirable procedure is' to mix the insoluble particles with resin and coupling agent in a hydrocarbon oil and to separately mix the soluble particles in water. In this way, after emplacement of the various layers, the resin is less likely to flow from one layer of insoluble particles to an adjacent layer of soluble particles.

Thus, it is preferred that one or more of the resins in liquid or particulate form be physically mixed with the insoluble particles and one or more coupling agents on the earth s surface and this mixture dispersed in a carrier fluid which is to form the slug from transmitting the insoluble particles from the earths surface into the fracture. a

The resin can be set up either by being subjected to heat or the action of a catalyst or both. The heat can come from the earth as geothermal heat, or as external heat from the surface of the, earth such as by pumping steam down the wellbore, or both as desired and convenient. The catalyst or curing agent can be supplied from the earths surface through the wellbore or, depending upon the composition of the naturally occurring fluid in the well, can come from the fractured formation itself, or both as desired and available. Combinations of heat and catalyst can also be employed such as in the situation where the stabilizing resin is a thermosetting resin and there is some but not sufficient geothermal heat available and it is more convenient to introduce a catalyst which when combined with the geothermal heat present in the formation is sufficient to cause the resin to set up to the desired extent. Thus,

the resin is normally set up after the layer emplacing procedure is completed and during and/or after dissolving the soluble layers. For example, with certain resinshydrochloric acid can be used to dissolve the soluble layers and at the same time act as a catalyst to set up the resin. Alternatively, the soluble layers can be dissolved after which the resin is treated to set it up.

Suitable thermosetting and/or catalytic setting resins include phenolic resins such as hydroxy arylaldehyde condensation products; hydroxy alkylaryl aldehyde condensation products and the like; urea aldehyde; amine aldehyde; acrylic resin such as those prepared from methyl methacrylate, ethylacrylate, n-butyl methacrylate, isobutyl methacrylate, ethyl methacrylate and similar esters, alone or in combination with other monomers; vinyl resins such as those prepared from vinyl chloride, vinyl acetate, vinyl alcohol, vinyl acetal, vinyl butyral, vinyl formal, vinylidene chloride, and the like; allyl resins such as allyl diglycol carbonate; alkyl resins such as glyceryl phthalate and the like; furan resins; polyepoxide resins such as those fully and completely disclosed in U.S. Pat. No. 3,391,738, the disclo-' sure of which is incorporated herein by reference; polyester resins such as those prepared by the copolymerization of a dihydride alcohol such as ethylene glycol, and unsaturated dibasic acids such as fumaric acid and an unsaturated monomer, such as styrene, and the like; polyisocyanate resins such as polyurethane derived from polyisocyanates such as toluene diisocyanate and polyols including gylcols, polyesters and polyethers; silicone resins such as those produced by the hydrolysis and condensation of organosilanehalide intermediates; styrene resins including both homoplymers and copolymers; furfuryl alcohol resins such .as furfuryl alcohol reacted with formaldehyde, with urea and formaldehyde, with phenol and formaldehyde or with one or more compounds containing two or more epoxy groups; and furfural resins. These resins are either thermosettingor catalytic setting or both. For example, polyepoxides can be set or otherwise hardened by treatment with amines, dibasic acids, acid anhydrides, and the like as fully and completely disclosed in said U.S. Pat. No. 3,391,738 while the furfural alcohol resins can be set up by treatment with hydrogen chloride, acyl halides such as methyl chloride, boron .trifluoride, boron trichloride, sulfur dioxide, hydrogen sulfide, other similar Lewis acids, and thelike. Phenolic resins, aldehyde resins, and the like are therrnosetting but oftentimes can also be treated with a catalyst to promote the setting up process. For example, an alkali catalyst such as sodium hydroxide can be added as a catalyst for these thermo setting resins. The thermosetting resins can, however, generally be set up by subjecting same to heat for a finite period of time in the absence of any catalyst. Preferred stabilizing resins are phenol formaldehyde, urea formaldehyde, and phenol furfural.

The amounts of stabilizing resin or resins employed vary quite widely depending upon the particular resins used, the particular insoluble particles used, the amount of insoluble particles used, the method by which the resin is to be set up, the desired degree of hardness to be achieved in the final treated insoluble particle layer, and the like. Generally, sufficient resin or resins will be employed so that the insoluble particles in the final layer will substantially resist movement toward the wellbore under the action of fluid produced through the fracture into the wellbore.

The particular setting up or curing process employed on the resin will vary widely again as well the specifics of that process, i.e., the temperature to which the resin is heated, the time for which the resin is heated, the amount of catalysts employed, the form of the catalyst employed, and the like. The resins useful in this invention are known in the art as are their compositions and properties so that one skilled in the art can determine the amount of resin to be employed and the particular curing process to be employed once the resin or resins to be used is known. The resins being known and commercially available, further discussion as to them and their curing processes is unnecessary to inform the art and therefore are omitted.

EXAMPLE A permeable and porous subsurface formation is fractured using diesel fuel as the fracturing fluid. After the fracture is formed and widened to the desired onetenth inch at the wellbore wall, the pressure on the diesel fuel is maintained by continuous addition of diesel fuel under pressure to the wellbore to replace diesel fuel which leaks off into the formation.

A slug of diesel fuel containing 7000 pounds of sand (passing a 20-mesh sieve and retained on a 40-mesh sieve), 3 gallons of silane coupling agent and 35 gallons of phenolic resin is mixed at ambient temperature and pressure and then introduced into the wellbore and fracture to form a first lower layer about 12 feet in height of resin-treated sand in the fracture. Thereafter, a second slug of diesel fuel containing 600 pounds of aragonite (a naturally occurring particle-form limestone) is mixed and then introduced into the wellbore and fracture to provide a second layer on top of and contiguous with the first layer, the second layer being about one foot in height and constituting the layer of soluble particles. Thereafter, a third slug of diesel fuel is mixed containing 3,000 pounds of sand of the same character used in the first slug, 15 gallons of phenolic resin, and 1.2 gallons of silane coupling agent. This slug is then introduced into the wellbore and fracture to form a layer about 5 feet in height above and contiguous with the second layer. Thus, the first and second layers of insoluble particles are spaced apart from one another in the fracture by the soluble layer of aragonite.

After'the desired amount of soluble and insoluble particles are injected, the pressure of the fracturing fluid is reduced so that the naturally occurring stresses in the formation take over and tend to force the two faces of the fracture toward one another thereby putting the three layers of particles under substantial compressive force.

' Thereafter, 1000 gallons of percent hydrochloric acid is injected into the formation and fracture at a low rate so that the fracturewalls are not forced open to dislodge the particles. The acid serves two functions. It dissolves the aragonite second layer thereby leaving an open conduit about one foot in height in the fracture between the first and second layers of sand, and-it causes the resin to set up, thus stabilizing the two layers of sand.

1 Normal production of the well is then taken up whereby fluids existing in the formation migrate from the formation into the fracture and flow to the wellbore through the insoluble sand layers as well as the open conduit left by removal of the aragonite.

The flow of fluid through the sand layers and the open conduit is substantial as to volume and velocity but the sand in the first and third layers in the fracture is retained in place inspite of the force supplied by the produced fluid due to the hardened resin. Thus, substantially none of the sand in the first and third layers is produced back into the wellbore.

Reasonable variations and modifications are possible within thescope of this disclosure without departing from the spirit and scope of this invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A method for increasing the permeability of a subsurface earth forrnation to fluid, said formation having a wellbore therein and at least one substantially upright fracture extending from the wellbore into said formation, said method comprising introducing into said fracture at least two discrete slugs of a carrier fluid mixed with solid particles which are substantially insoluble in a preselected fluid to thereby deposit in said fracture at least two layers of said substantially insoluble particles, introducing into said fracture in alternate sequence with said discrete slugs of substantially insoluble particles at least one slug of a carrier fluid mixed with solid particles which are essentially soluble in said preselected fluid so that there is deposited in said fracture alternating layers of said insoluble particles and said soluble particles, said carrier fluid for said slugs being substantially a nonsolvent for said soluble particles, providing at least one of said layers of insoluble particles with a stabilizing resin which can be set up to physically stabilize said at least one insoluble particle layer to resist movement of said insoluble particles toward said wellbore during subsequent production of fluid through said fracture into said wellbore, setting up said stabilizing resin in said at leastone insoluble particle layer, and removing at least part of said soluble particles.

2. A method-according to claim 1 wherein each layer of said insoluble particles is provided with said stabilizing resin before the next adjacent layer of soluble particles is emplaced in said fracture.

3. A method according to claim 1 wherein said stabilizing resin is a thermosetting resin, and setting said resin by heating same after emplacement of said resin in said fracture.

4. A method according to claim 3 wherein said heating is provided by geothermal heat.

5. A method according to claim 1 wherein said stabilizing resin is a catalytic setting resin, and setting said resin by treating same with a catalyst after emplacement of said resin in said fracture.

6. A method according to claim 1 wherein said stabilizing resin is a catalytic setting resin, and setting said resin by treating same with a catalyst which also dissolves at least part of said soluble particles.

7. A method according to claim 6 wherein hydrochloric acid is both said catalyst and said soluble particle solvent.

8. A method according to claim 1 wherein said insoluble particles, resin, and catalyst are mixed together on the earths surface and then introduced into said fracture after whichsaid resin is set up.

' 9. A method according to claim 8 wherein said resin is set up by geothermal heating in said fracture.

10. A method according to claim 1 wherein said stabilizing resin is both a thermosetting and a catalytic setting resin, and setting said resin by treating said resin with at least one of heat and catalyst after emplacement of said resin in said fracture.

11. A method according to claim 1 wherein said stabilizing resin is at least one resin selected from the group consisting of phenolic resin, urea aldehyde, amine aldehyde, acrylic resin, vinyl resin, allyl resin, alkyl resin, furan resin, polyepoxide resin, polyisocyanate resin, polyester resin, silicone resin, styrene resin, furfuryl alcohol resin, and furfural resin.

12. A method according to claim 11 wherein said at least one resin is set up using at least one of heat and v a catalyst.

13. A method according to laim l 1 wherein said resin and insoluble particles are intimately mixed with one another in the absence of carrier fluid to resin wet the insoluble particles with said resin before said insoluble particles are exposed to said carrier fluid.

14. A method according to claim 13 wherein said resin and insoluble particles are mixed in the presence of an effective amount of at least one coupling agent and in the absence of said carrier fluid;

15. A method according to claim 1 wherein said stabilizing resin is mixed with said insoluble particles on the earth s surface before emplacement of said insoluble particles into said fracture. V

16. A method according to claim 15 wherein said mixture of resin and insoluble particles is additionally mixed with carrier fluid before emplacement into said fracture. v

17. A method according to claim 15 wherein said resin is mixed with both said insoluble particles and an least one coupling agent.

Claims

2. A method according to claim 1 wherein each layer of said insoluble particles is provided with said stabilizing resin before the next adjacent layer of soluble particles is emplaced in said fracture.
3. A method according to claim 1 wherein said stabilizing resin is a thermosetting resin, and setting said resin by heating same after emplacement of said resin in said fracture.
4. A method according to claim 3 wherein said heating is provided by geothermal heat.
5. A method according to claim 1 wherein said stabilizing resin is a catalytic setting resin, and setting said resin by treating same with a catalyst after emplacement of said resin in said fracture.
6. A method according to claim 1 wherein said stabilizing resin is a catalytic setting resin, and setting said resin by treating same with a catalyst which also dissolves at least part of said soluble particles.
7. A method according to claim 6 wherein hydrochloric acid is both said catalyst and said soluble particle solvent.
8. A method according to claim 1 wherein said insoluble particles, resin, and catalyst are mixed together on the earth''s surface and then introduced into said fracture after which said resin is set up.
9. A method according to claim 8 wherein said resin is set up by geothermal heating in said fracture.
10. A method according to claim 1 wherein said stabilizing resin is both a thermosetting and a catalytic setting resin, and setting said resin by treating said resin with at least one of heat and catalyst after emplacement of said resin in said fracture.
11. A method according to claim 1 wherein said stabilizing resin is at least one resin selected from the group consisting of phenolic resin, urea aldehyde, amine aldehyde, acrylic resin, vinyl resin, allyl resin, alkyl resin, furan resin, polyepoxide resin, polyisocyanate resin, polyester resin, silicone resin, styrene resin, furfuryl alcohol resin, and furfural resin.
12. A method according to claim 11 wherein said at least one resin is set up using at least one of heat and a catalyst.
13. A method according to laim 11 wherein said resin and insoluble particles are intimately mixed with one another in the absence of carrier fluid to resin wet the insoluble particles with said resin before said insoluble particles are exposed to said carrier fluid.
14. A method according to claim 13 wherein said resin and insoluble particles are mixed in the presence of an effective amount of at least one coupling agent and in the absence of said carrier fluid.
15. A method according to claim 1 wherein said stabilizing resin is mixed with said insoluble particles on the earth''s surface before emplacement of said insoluble particles into said fracture.
16. A method according to claim 15 wherein said mixture of resin and insoluble particles is additionally mixed with carrier fluid before emplacement into said fracture.
17. A method according to claim 15 wherein said resin is mixed with both said insoluble particles and an effective amount of at least one coupling agent.
18. A method according to claim 1 wherein said stabilizing resin is at least one of phenol formaldehyde, urea formaldehyde, and phenol furfural.
19. A method according to claim 1 wherein said stabilizing resin is at least one of furfuryl alcohol resin and polyepoxide resin, and said resin is set up by contacting same with a catalyst after emplacement of said resin and insoluble particles in said fracture.
20. A method according to claim 1 wherein said insoluble particle slugs contain an effective amount of at least one coupling agent.