US2664954A - Hydraulic fracturing to increase well productivity - Google Patents

Description

Jan. 5, 195

E. A JOHNSON HYDRAULIC FRACTURING TO INCREASE WELL PRODUCTIVITY Filed Dec. 31, 1949 2 Sheets-Sheet 2 JNVENTOR.

t a/areff 4. Johnsan Patented Jan. 5, 1954 sips HYDRAULIC FRACTURING TO INCREASE WELL PRODUCTIVITY Everett A. Johnson, Park Ridge, 111., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana Application December 31, 1949, Serial No. 136,211

8 Claims. (01. 166-21) This invention relates to improved method and means for increasing the productivity of fluids from strata traversed by wells, such as oil wells or gas wells, and it pertains more particularly to improvements in the method of fracturing channels in the traversed strata by means of lowpenetrating liquids and in purging such liquids from the fractured formations.

Many methods have been heretofore proposed for increasing the drainage area within a selected producing zone of an oil or gas well. For example, explosives have been detonated within a well to enlarge the well diameter and in an attempt to fracture formations immediately adjacent the well. The use of explosives, however, is unsatisfactory for economic reasons and because of the tendency of explosives to shatter and seal the exposed face of the formation. Horizontal drilling likewise has been proposed for increasing the drainage area of a well in a selected zone, but such a system requires cumbersome apparatus, does not find general application, and the increased productivity is rarely commensurate with the increased cost of drilling. Acidizing is sometimes practiced to increase permeability of certain types of formations immediately adjacent the well bore, but this process is limited to use in calcareous formations. Thus each of these processes is limited in its effectiveness for extending drainage channels or fractures an appreciable distance into the well formation. However, recently a process has been developed for hydraulically fracturing the selected formation to produce laterally extending channels in a cheap and economical process. Such a process is described, for example, in the Oil and Gas Journal, volume 47, No. 2 p. 76 et seq. (October 14, 11948).

In the hydraulic fracturing of a formation adjacent a well it is important that the fluid does not penetrate into the formation too rapidly because this precludes attaining the necessary fracturing pressure. Therefore the fluid is as viscous as practicable. However, it is necessary to remove the hydraulic fiuid from the fracture because it tends to plug the producing formation. Heretofore this has been attempted by following the gelled gasoline with gel breaker which is forced under hydraulic pressure into the formation behind the gel. In some instances this has merely resulted in forcing the gel further into the formation and it is not possible to remove all the plugging gel from the producing zone. Hence, it has heretofore been important that the viscous hydraulic liquid should not penetrate too far into the produced channel because that made subsequent removal difficult. It is therefore an object of my invention to provide an improved system for removal of the fracturing fluid which is not limited by the viscosity and which therefore permits greater lateral penetration of the fracture.

A specific object of my invention is to provide an improved system for the positive displacement of the viscous liquid from the produced fracture. These and other objects of my invention will become apparent as the description thereof proceeds.

In m process I employ a low-penetrating fluid such as a high-viscosity liquid or gel to fracture the formation and then remove the gel or liquid from the fracture by positive displacement thereof toward the well instead of aWay from the well as heretofore practiced. To displace the lowpenetrating fluid from the fracture I inject a high-penetrating fluid into the formation at a point spaced vertically from the fracture and cause the high-penetrating fluid to be produced from the fracture into the well. I accomplish this by means of the apparatus illustrated in the drawing wherein:

Figure 1 shows a diagrammatic arrangement of tubing and packers within a cased well for applying hydraulic pressure to the formation;

Figure 2 schematically illustrates the apparatus and flow of fluids during the fracture-cleaning operation;

Figure 3 shows an arrangement of apparatus employing a pair of spaced packers in a well for the application of the hydraulic pressure between the packers; and

Figure i illustrates the fracture-cleaning operation when using the apparatus of Figure 3.

In each of Figures 2, 3, and 4c, the apparatus at the surface is the same as that shown in con nection with Figure l.

The fracturing fiuid comprising a low-pene trating fluid is pumped into an isolated portion of the formation to be fractured. Sufficient pressure, e. g. 1,000 to 15,000 p. s. i., is applied to the low-penetrating gel until the formation breakdown pressure is reached, at which time, as a general rule, the surface pressure decreases abruptly and levels off at a substantially constant value upon the continued injection of the lowpenetrating fluid to extend the fracture.

After the formation has been fractured and the fracture has been extended by the injection of a substantial quantity of low-penetrating fluid mto the Well, the removal of the gelled fluid is effected by my novel technique. More specifically, a high-penetrating liquid is injected under pressure into a zone vertically displaced a distance from the fracture. Such a liquid is characterized by having very low viscosity and capable of entering the traversed formations under relatively low pressure. In other words, I inject a liquid of high penetrating propertie into the formation adjacent the fracture containing the viscous liquid. 7

Ordinarily the vertical distance chosen is sufficient to avoid a simple bypassing of the packer by the high-penetrating liquid. However, the gel itself will act as a temporary barrier and cause the high-penetrating liquid to travel laterally a substantial distance from the well before it migrates vertically into the formation fracture and is produced from the fracture into the well. After the flow has been established, a substantial volume of high-penetrating liquid is pumped into the formation. A circulation or migration of the low-viscosity liquid can be set up within the formation into the fracture and the gelled liquid is thus rendered less viscous by dilution or by gel breaking and can be removed from the fracture.

The term low penetrating fluid as employed herein means a fluid which has a greater viscosity than water, crude oil, or ordinary well fluids, and whose tendency to filter through a formation is materially less than that tendency of normal well fluids. Newtonian liquids may be considered low penetrating when they have a viscosity substantially greater than 30 centipoises and in the range of about 50 to 5000 centipoises, more viscous fluids being undesirable because their pumpability is more difficult. A test for determining the penetration properties of a fluid is carried out by placing 600 cc. of the fluid in a standard cylinder above a supported Whatman #50 filter paper, and applying a gas pressure of 100 pounds per square inch at the top of the column. Ordinary crude oils and oil field brines are forced through the filter paper in about to seconds, this time interval being referred to as dehydration time. A low penetrating fluid in this test must have a dehydration time of at least about two minutes. For best results the dehydration time should be in excess of 30 minutes, and even at 30 minutes the fluid loss is preferably less than 100 cc.

The low penetratin liquids of my invention may be organic liquids containing a sufiicient amount of organophilic bentonites or salts of fatty acids to meet the above dehydration and preferably the fluid loss requirements.

Organophilic bentonites per se are well known in the art (note Journal of Physical and Colloid Chemistry, vol. 53, No. 2, pp. 294306) and are marketed as bentones, a typical example being bentone 34 which is a bentonite with inorganic cations base-exchanged with dimethyldiheptadecylammonium ions. Such an organophilic bentonite may be produced by dispersing an ordinary Wyoming bentonite in water to obtain a substantially complete separation of the bentonite platelets, filtering any quartz or other extraneous matter, adding (CH3)2(C17H35)2NC1, maintaining the added salt inintimate contact with the slurry for a sufficient period to obtain base exchange, removing the aqueous solution of inorganic salt, and washing inorganic salts out of the modified bentonite and drying the resulting product to powdered forrn. bio novelty is claimed in organophil'ic 'b entonites per se or their method of preparation, and further description thereof is therefore unnecessary.

Although the salts of fatty acids, in general, are suitable bodying agents for producing a 10W- penetrating fluid for use in my invention, a metal soap, such as a hydroxy aluminum soap is a preferred gelling agent since it has the ability to form hydrocarbon gels at ordinary temperatures.

About 0.5% to about 10% by weight of the hydroxy aluminum soap based upon the liquid, preferably between about 3% and about 6% of soap, produces a suitable gel. At about 75 F., for example, from about 3% to about 10% of the mixed soaps disperses in gasoline in from about 15 seconds to about 10 minutes, and gels of suitable viscosity and low liquid loss are produced from the dispersion after about 30 seconds to about 20 minutes.

High penetrating fluids, on the other hand, are low viscosity liquids such as gasoline, kerosene, toluene, benzene, etc. and may include fiuids actually produced in the wells. When soap gelled liquids are used, however, about 1% of a specific gel breaker such as a water-soluble amine or an oil soluble sulfonate, based upon the volume of low penetrating liquid in the formation, may be admixed with the high penetrating liquid to enhance the reduction of the viscosity of the lowpenetrating liquid.

Forms of apparatus suitable for use in accordance with my invention are shown in the drawings and referring to Figure 1, a casing H isset in well bore is and tubing i2 is run in with a packer 3 to isolate a portion of the stratum to be treated. The low-penetrating liquid is prepared at the well head as described above and introduced into tubing 12 by means of pump i l under a high pressure sufficient to form the fracture it During the fracturing operation a column of liquid can be maintained within the annulus between the tubing l2 and casing it so as to prevent collapse of the tubing I2 and to minimize any tendency of the low-penetrating fluid to bypass the packer it. This can be accomplished for example by introducing the high penetrating liquid into the casing ll via pump iii and closing the valve ll.

As a specific example of my invention I will describe how the invention may be applied in the treatment of an oil well in the East Texas field in which oil production has fallen to about one barrel of oil per day with no water. With a total well depth of 3550 feet, the twc-inch tubing 12 and casing ii may extend to a depth of 3500 feet and a packer is may be placed between the bottom of the well tube string l2 and the open hole l9, leaving an open hole below the packer E3 of about 4 /4. inches in diameter. The fracturing liquid is made up by adding an organophilic'bentone to about 25 barrels of benzene in a stirred tank (not shown). Crude oil may be employed instead of benzene if'sufflcient mixing or milling is employed to obtain the desired viscosity increase, or if the organophilic bentonite is swelled with a small amount of polar organic liquid such as nitrobenzene, simple paddle mixers may be employed or the mixing may be obtained by pumping the material from the bottom of the tank and returning it to an intermediate point.

When sufficient organophilic'bentone has been employed to give an apparent Stormer viscosity of approximately 209 centipoises, at 600 R. P. M., the liquid which is now a low-penetrating fluid is injected by pump Hi through the tubing i2. About pounds of 16 mesh plaster sand is preferably mixed with the fluid immediately before it is introduced into the well in order that it may serve as a prop in the fracture to be produced.

The gelled, low-penetrating liquid is followed by crude oil and crude oil is continuously pumped through the tubing l2 until formationbreak down p the is reached, which in this case is apprc; tely 3400 pounds per square inch on gage .Jhen the fracture occurs by virtue of the hydraulic pressure produced by pump 14, the pressure will of course drop, for example to approximately 2800 pounds per square inch. Further pumping at such a pressure level will extend the fracture E9 to the desired distance which be about 50 feet from the well it).

In prior processes it was necessary to allow the well to stand idle for as much as 48 hours in order to obtain the required reduction in viscosity of the fracturing liquid. In my process the low penetratin fracturing fluid can be removed almost immediately following the fracturing step. The removal of the fracturing fluid is accelerated by introducing a high penetrating liquid, such as gasolin or benzene, at a level adjacent but spaced from the fracture IS a distance Suicient to prevent short circuiting but to effect migration of the high penetrating liquid toward the remote flanks of the gel-filled fracture or channels. Jsually between about 2 and 5 volumes of penetrating liquid based on the o lie ted low penetrating fluid are used. netrating liquid is introduced into the fa tion through the annulus 24 while fiuids are being produced through the tubing 12 the pressure differential thus obtained facilitates a migration of the high-penetrating liquid into contact with the gel in the fracture l9. However,substantial pressure of at least about 100 p. s. i. above the formation pressure can also be applied by pump H3. The admixture of fluids is produced from the fracture via tubing :2 and accumulated at the surface where the diluent can be separated from the admixture whereby the gel is reformed for further use and the high penetrating liquid can be recycled.

In Figures 3 and i I have illustrated another form of apparatus wherein dual packers 20 and 2i are set on tubing l2 with ports 22 intermediate the packers. In the operation of this apparatus the packers 20 and 2! are first set at a relatively high point within the open hole I 0 and the low-penetrating fluid introduced via tubing 52 by apparatus described in connection with Figure 1. Subsequently the tubing string :2 and packers 2b and 22 are reset below the fracture 23 and the high penetrating liquid introduced into the formation via the tubing string i2 while producing fluids from the fracture 23 through the annulus 2 i and pump 16. Thus when the highpenetrating liquid is passed by pump l4 under pressure through the tubing i2 into the forma tion below the fracture 23, the high-penetrating fluid flows laterally and vertically as shown in Figure l into contact with the low-penetrating liquid in the fracture 23 and thence into the annulus 2d of the casing H. As described above the gel in the fracture 23 becomes diluted by the high-penetrating liquid and the admixture is produced from the fracture 23 into the well Ill, being pumped to the surface through the casing I l by pump it.

Although specific embodiments of my invention have been described it should be understood that these are by way of illustration only and that the invention is not limited thereto since alternative embodiments and operating techniques will become apparent to those skilled in the art in view of my disclosure. Accordingly, modifications of my invention are contemplated Without departing from the spirit of my described invention or the scope of the appended claims.

My copending application Serial No. 136,175, filed December 20, 1949, entitled Increasing Well Productivity and now abandoned in favor of this application also describes the organophilic bentonites and their uses in well operations.

What I claim is:

1. The method of treating wells which comprises introducing into the well bore a gelled fracturing medium consisting essentially of a lowviscosity hydrocarbon liquid and a gelling agent in an amount sufficient to effect gelation of said liquid, forming a lateral channel from the well bore into the formation by means of hydraulic pressure exerted on said fracturing medium, introducing at least a portion of the gelled medium into the produced lateral channel, injecting into the formation at a level spaced from said channel a second liquid characterized by being a solvent for the gelled medium and by having a tendency to filter rapidly into the formation without any substantial build-up of pressure, said second liquid thereby flowing laterally from the well here toward said channel whereby the viscosity of said medium is substantially reduced, flowing the medium of reduced viscosity inwardly through said channel into said well bore, and removing the admixture from the well bore.

2. The method of claim 1 wherein the gelling agent consists essentially of salts of fatty acids.

3. The method of treating wells which comprises introducing into the well bore a gelled fracturing medium consisting essentially of a low-viscosity hydrocarbon liquid and an organephilic clay obtained by base exchange between onium compounds and the clay in an amount sufficient to effect gelation of said liquid, forming a lateral channel from the well bore into the formation by means of hydraulic pressure exerted on said fracturing medium, introducing at least a portion of the gelled medium into the produced lateral channel, injecting into the formation at a level spaced from said channel a second liquid characterized by being a solvent for the gelled medium and by having a tendency to filter rapidly into the formation Without any substantial build-up of pressure, said second liquid thereby flowing laterally from the well bore toward said channel whereby the viscosity of said medium is substantially reduced, flowing the medium of reduced viscosity inwardly through said channel into said well bore, and removing the admixture from the Well bore.

4. The method of claim 3 which includes separating the admixture to restore the high viscosity and gel-like characteristics of the fracturing medium, and employing the restored fracturing medium in a subsequent well treating operation.

5. The method of increasing the productivity of an oil producing formation traversed by a dually completed well which comprises the steps of isolating a first zone of an exposed portion of the formation, introducing into said isolated first zone a quantity of a gelled hydrocarbon liquid, applying hydraulic pressure to said gelled hydrocarbon liquid sufiicient to fracture the traversed formation in the region of the said first zone and to inject at least a part of said gelled hydrocarbon liquid into the produced fracture, isolating a second zone of the exposed portion of the traversed formation adjacent said produced fracture, injecting a quantity of a high penetrating fluid into said second isolated zone, said highpenetrating fluid comprising a liquidsolvent for reducing the viscosity of the gelled hydrocarbon liquid, continuing the injection of the highpenetrating liquid into the said second-isolated zone causing the high-penetrating fluid to flow laterally and longitudinally into contact with the low-penetrating gelled hydrocarbon liquid disposed within the produced fracture whereby the viscosity of the gelled hydrocarbon liquid is greatly reduced, and simultaneously withdrawing the hydrocarbon liquid of reduced viscosity and the high-penetrating liquid from the said fracture into the well to produce a highly permeable channel extending from said formation at the level of said first zone.

6. The method of increasing the productivity of a formation traversed by a well bore which comprises introducing into the well bore a gelled fracturing medium consisting essentiallyoi liquid benzene and an organic organOphilicmontmorillonite clay obtained by base exchange between oniurn compounds and the clay in an amount suflicient to effect gelation of said liquid benzene to give a viscosity of at least about 200 centipoises, forming a lateral channel from the well bore into the formation by means of hydraulic pressure exerted on said fracturing medium, introducing at least a portion of the fracturing medium into the produced lateral channel, injecting into the formation at a level spaced from said channel a quantity of liquid benzene characterized by being a solvent for the gelled medium and by having a tendency to filter rapidly into the formation without any substantial build-up of pressure, said quantity of liquid benzene thereby flowing laterally from the well bore towards said channel whereby the viscosity of said medium is substantially reduced, flowing the fracturing medium of reduced viscosity inward through said channel into said well bore, and removing the admixture from the Well bore.

'7. In the method of completing a well which has been drilled into a potentially productive formation, the steps which comprise, running tubing and a packer to the exposed'formation, placing a gelled liquid fracturing medium :adjacent the formation below the packer, hydraulically fracturing the formation by applyinghydrostatic pressure to the fracturing medium adjacent the potentially productive formation, flowing a portion of the fracturing medium into the produced fracture, introducing a high-penetrating liquid solvent for the said medium into the annulus above the packer, applying pressure to the high-penetrating liquid whereby it passes through the formation adjacent the fracture and migrates into contact with the said medium, and while injecting the high-penetrating liquid through the formation, producing fluids from said fracture whereby the said medium is purged therefrom and withdrawn from the well via the tubing.

8, In the method of completing a well, the steps which comprise drilling a well bore into a potential productive formation, setting casing in said bore to a point above the said formation, running tubing to the productive formation, setting a packer to isolate the formation therebelow, placing a hydrocarbon gel below the packer and adjacent the formation, hydraulically fracturing the formation by applying hydrostatic pressure to the gel adjacent the potentially productive formation, perforating the casing above the packer, introducing a high-penetrating liquid solvent for the gel into the annulus between the r casing and the tubing, applying pressure to the high-penetrating liquid whereby it passes through the perforations into the formation adjacent the fracture,.and contiuing the injection of the high-penetrating liquid into contact with the gel in the fracture while producing the well through the tubing whereby the gel is purged therefrom and withdrawn via the fracture into the tubing.

EVERETT A. JOHNSON.

References Cited in theme of this patent UNITED STATES PATENTS Number Name Date 1,661,270 Ryder et al Mar. 6, 1928 1,816,260 Lee July 28, 1931 2,104,328 Kotzebue Jan. 4, 1938 2,171,416 Lee Aug. 29, 1939 OTHER REFERENCES

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