US3066733A

US3066733A - Method of explosively fracturing a productive oil and gas formation

Info

Publication number: US3066733A
Application number: US736701A
Authority: US
Inventors: Clarence W Brandon
Original assignee: Individual
Current assignee: Individual
Priority date: 1958-05-21
Filing date: 1958-05-21
Publication date: 1962-12-04
Anticipated expiration: 1979-12-04

Description

3,066,733 DUCTIVE Dec. 4,1962

C. W. BRANDON OSIVELY FRA METHOD OF EXPL CTURING A PRO OIL AND GAS FORMATION Filed May 21, 1958 MZFUDOOEQ ZOZ M2 PO 300mmwskmhm mmmmnm l III I lily I I ED E wzEbhum INVENTOR. CLARENCE W. BRANDON ATTORNEYS United States Patent dine Patented Dec. 4, 196.?

3,066,733 METHOD OF EXPLOSIVELY FRACTURIING A PRODUCTHVE UlL AND GAS FGRMATION Clarence W. Brandon, Tulsa, Gilda. (525 ()aldand Ave, Tallahassee, Fla.) Filed May 21, 1958, Ser. No. 736,701 19 Claims. (Cl. 166-36) The present invention relates to methods employing explosives detonated in formations adjacent to but separated from productive oil and gas horizons by a portion of non-productive strata for effective controlled fracturing of the horizons.

Through research and development, productive oil and gas formations have been fractured by placing explosives directly in the oil and gas strata and exploding them from within the strata. In this method it has been found that due to the permeable conditon of the producing strata, the explosive enters into the pore space of the formation and mixes with the fluid of the formaton, becoming so thinly divided that detonation of all of the explosives introduced into the fracture in the formation is prevented. A further problem with this method has been that in a producing strata wherein the sand is of a silicious nature, the abruptness of the detonation is such that the strata disintegrates into sand almost in a body adjacent the well bore, and production of fluids from the formation thereafter is actually reduced or prevented by the large accumulation of sand coming to the well bore.

In one well in the Spraberry oil fields of West Texas, wherein explosives were introduced into the existing fractures in the productive strata, after extension of and/or enlargement of these fractures were caused by forcing thereinto a fracturing fluid, then after detonating the explosive it required several months for the operator of the well to clean out the pulverized and disintegrated formation that came to the well bore. In this well the several hundred feet of productive Spraberry strata, and the numerous natural fractures therein, required the introduction of a large amount of explosives in order to attempt to fracture the matrix of the productive strata for a distance back from the well bore.

In instances where the explosive has been introduced into a producing strata of calcarous nature, the abrupt detonation of the explosive tends to compact the formation both above and below the fracture wherein the explosive has been placed so that rather than causing an increase of permeability adjacent the well bore, which is the desired result in most fracturing operations, it compacts or sears the formation within an area adjacent to the explosion. Such a compacting, or searing results in substantially no increase of over-all permeability and no increase in production of fluids at the well bore.

The primary object of the present invention is to introduce an explosive into a created fracture, or interface between stratas, in a portion of a formation adjacent to but separated from a permeable and productive oil and gas strata by a portion of non-productive strata, and to detonate the explosive to fracture the productive horizon.

Another object of the invention is to introduce a fluid into a barren portion of the formation adjacent a productive strata and to follow the fluid with an explosive which is then detonated to force the introduced fluid further into the barren portion of the formation to create a fracturing force on the productive strata.

Another object of the invention is to mix a dehydrating additive into the fluid introduced into the formation in advance of the explosive material in order to cause a more abrupt force to the fluid when it is compressed and compacted back into the formation, by the force of the ex plosion.

A further object of the invention is to utilize a substantially resilient barren formation that is adjacent to but separated from a productive gas and oil strata by a portion of non-productive strata, by creating a fracture therein, or entering an interface thereof, with explosive media and thereby explosively compacting and arching the deformable strata between the fracture or interface, and the productive strata, to thus more fully fracture the substantially non-deformable and non-compressible productive strata.

A still further object of the invention is to leave send as a propping agent in the barren formation prior to the introduction of the explosives, to more easily allow the introduction of fluid explosives into a fracture in a barren formation adjacent a productive horizon.

Another object of the invention is to place an explosive in such a way in a fracture in a formation adjacent to but separated from a productive strata by a portion of non-productive strata, so that the explosive force will cause both vertical and block fracturing of the productive strata.

Still another object of the present invention is to carefully select the explosive receiving type of strata and distance thereof from the productive horizon, with the distance and type of strata used providing a cushion buffer zone, which is a variable of the amount and kind of explosive used and the thickness and characteristic of the productive horizon, as well as the type, locality and area of the fracture desired in the productive horizon.

A still further object of the present invention is to mix sand with a fluid explosive prior to introduction into a formation in order to use the sand as a propelled and compacting agent to further the explosive effect in fracturing of the productive strata.

A further object of the invention is to explosively, additionally fracture a productive horizon, having existing natural fractures therein caused by folding and thrust, by placing and detonating explosives at a point in the formation that is adjacent but separated from the productive horizon by a portion of non-productive strata, and so placing the explosives in such a position that the explosive force, upon detonation, will be against the areas of natural folding and/ or thrust so as to cause momentary closure of some of the fractures within the productive horizon.

An object of the invention is to introduce separate charges of explosives into formations adjacent to but separated from productive strata by a portion of nonproductive strata both above and below the productive strata and then detonate the charges of explosives at timed intervals. The timed explosions create shock waves which meet in the productive strata at preselected phase angles and thereby cause variably controllable cancellation, reinforcement or augmentation of the explosive shock wave. effects within the productive strata.

Another object of the invention is to place two or more charges of explosives in a formation adjacent to but separated from a productive strata by a portion of non-productive strata on one side only of the productive strata and detonate the explosives at timed intervals. The timed explosion create various phase angles of shock wave in order to produce a shock Wave in the productive strata that is complemented, reinforced or augmented as to total explosive force so as to fracture said productive strata.

A still further object of the invention is to place charges of explosives, in accordance with any and all of the above objects, in a plurality of well bores, detonating the explosives at various phase angles of shock wave to each other so as to cause a variable controlled form of shock Waves to be expended within the formation between said wells for the purpose of fracturing the productive horizon that the well bores intercept.

Another object of the invention is to place charges of explosives in various well bores, as set forth above, with a portion of the charges being below the productive horizon in a well bore and a portion thereof being above the productive horizon in separate well bores, whereupon variable detonating of the different charges of explosives will cause controllable, formation fracturing shock waves to be produced in the productive horizon between the well bores.

These and other objects of this invention will become apparent from the following description in conjunction with the accompanying drawings of which:

FIGURE 1 is a schematic diagram partially in crosssection describing phases of a method according to this invention.

FIGURE 2 is a similar schematic diagram partially in cross-section showing an additional phase of a typical method of practicing this invention.

Referring now to FIGURE 1, the numeral in designates a subterranean formation containing oil and/ or gas. Vertically spaced, either downwardly or upwardly as shown, is a non-productive strata comprising as an example, a relatively deformable and compressible strata 12 which is separated from the producing strata ltl by a third or buffer strata 14. Typically, these formations are penetrated by a well 16 having a protective string of casing 18 therein. Tubing 2%) is adapted to be positioned with its lower end 22 opposite the uppermost formation 12 and within the space confined by

packing elements

24 and 26. The location of the various strata, their characteristics, and the placement of the packing elements 24 and 2'6 with respect to the lower to confine the perforated tubing end 22 is determined from well known logging methods and techniques. The upper end of the tubing 2t) at the surface is attached to a pump 36. A pressure gage 32 is in communication with the interior of the tubing for use in connection with the processes. Diagrammatically shown attached to the intake of the pump 36 is a fracturing system generally shown as 34, as used to from fracture t) and an explosive system generally shown as 36.

In FIGURE 2 a further sequential phase of the invention is shown with specific regard to the use of a detonation means 4%, such as an explosive, which is controllably positioned within the well at the desired position between packing elements 243- and 26 by a wire line 42 from the surface. Additionally, the result of the process is diagrammatically illustrated to shOW the resultant fractures 44 in the productive formation 10.

It is well known in the art of fracturing wells for the increase of the production of oil and gas therefrom that a substantial portion of the producing horizons are of a relatively non-compressive and non-deformable nature. Adjacent these productive stratas there are in most instances stratas that are highly compressible and deformable, due to the heat and pressures existing in the depths of the earth at which these stratas are situated, and under the abrupt detonation of an explosive, these stratas will compact, deform, flow, arch and distort with practically no fracture being created therein by the explosive force.

Although the principles and operation of this invention are enhanced by injecting the explosives into a relatively deformable and compressible barren strata that is adjacent a substantially non-compressible and nondeformable productive oil and gas horizon, yet the invention is not limited thereto but covers broadly the creation of a fracture or the use of an interface between nonproductive strata in a portion of the formation that is adjacent to but separated from the productive oil and gas horizon by a portion of non-productive strata, and the injection of an explosive into said fracture, or interface, so as to allow for and form a cushion between the abruptness of the detonated explosive and the productive horizon, as well as to cause an extension of the force eaves d of the explosion over a larger area, and thus more completely fracture the productive horizon.

In some instances it might be desirable to force a fracturing fluid into the formation adjacent the productive strata in order to create the fracture, subsequently removing the fracturing fluid, and then introduce the explosive. In other methods of operation it might be desirable to introduce the fracturing fluid to cause a fracture in the barren formation, following thereafter with the introduction of sand of predetermined amounts in fluid and then follow thereafter with the introduction of the explosive. In other instances it would be desirable to withdraw the fluid used to transport the sand into the fracture, leaving the sand as a propping agent, and then introduce the explosive into the propped open fracture. The formation of a fracture for the introduction of explosives thereafter is not limited to any particular fracturing method. In some instances the fractures are created by any of the various methods taught in the United States patents to Farris, Resissue 23,733; Vorhees, 2,645,291; Clark, 2,596,- 844; Bond, 2,672,936; Johnson, 2,664,954; or Abendorth, 2,693,854. Also, where the explosive is of a proper fluid consistency the sand could be mixed with the explosives so that upon detonation the force of the explosion would use the sand as a propelled and compacting agent to extend the area and force of the explosion in the barren strata, and thus cause a resultant increase and extension of the fracture of the productive formation.

In the practice of using an interface between strata into which to inject the explosives, there is sometimes encountered connate water therein that will dilute or thin the explosives and/or the fluids used to practice some of the methods of this invention. In such cases, dehydrating or water absorbing agents are added to the fluids, such as the fracturing fluids being pumped into the formation. Typical of such agents are bentonite, alcohol, or agents which will increase the interfacial tension between the water and formation to form a rather abrupt face to the fluids being pumped into the interface where fluids are used ahead of the explosives, and a correspondingly more abrupt force will be given to the leading face of the fluid upon detonation of the explosive.

The present invention does not concern itself with the specific means of introducing explosives into the created fracture, as the art thereon is fairly well known and is practised considerably at present. While nitroglycerine, picric acid, or other liquid explosives may be adequately prepared and employed in this invention, solid explosives such trinitrotoluene may be used alone or dispersed in suitable inert solvents for placement in a created fracture.

t is possible to perforate cemented casing at the desired place in the barren formation, then create a fracture, pump thereafter explosives into the fracture and then follow the explosives down the casing or tubing with a plug, thereafter forcing fluid behind the plug, pushing the explosives out into the created fracture. Detonation of the explosives in the fracture could be done by any of the several well known ways practised at present, or can be effected by following the explosive, or combining therewith, a delayed action chemical detonating means, so that fluid following the explosives and the detonating means could force these away from the perforations adjacent the well bore and thus prevent damage to the portion of the casing passing through the productive strata, when the explosion is consummated. Thereafter the cemented casing can be perforated where production is desired and the well produced.

One specific method of this invention is best described with reference to FIGURES l and 2 and quite generally includes the following steps:

(1) The location and identity of productive formation in and the vertically

adjacent formations

12 and 14.

(2) Tubing Eli and

packing elements

24 and 26 are located to substantially straddle the formation 12.

(3 The formation 12 is caused to be fractured as shown by the numeral 50 by adequate connection of the pump 30 with the fracturing fluid system 34.

(4) The explosive media system is then forced by pump 30 into the existing fracture 50.

(5) The explosive is detonated, and

(6) Oil and/or gas is produced from the formation 10.

Another method of operation of the present invention is that the productive strata and the adjacent formation in which the fracture is created can be left, open hole, with no casing cemented in place through this part of the formation, and the fracturing done through tubing set on various types of packers that can be used to isolate the barren formation, and the fracturing fluid and/or the explosives can be introduced through this tubing. This last means being an alternative Way to prevent collapse of casing adjacent the productive strata. Another method would be to cement the easing into place above the productive strata and the adjacent formation, complete the well bore open hole and proceed as above.

The creation of the fracture in the formation which is adjacent the productive strata, in order to enable the introduction of the explosives, can be above and/or below the productive horizon, although in most instances it would be desirable to create the fracture in the formation below the oil and gas production strata.

In order to allow a clearer understanding of the teachings of the invention, there is described below an application of the methods of this invention to an improved means of fracturing the earlier cited Spraberry well of West Texas, wherein pulverized and disintegrated formation coming to the well bore was so bad that it prevented the operator from producing from the well for a period of months.

It is generally understood that the Spraberry oil fields of West Texas are situated on an extensive monocline, and due to the low permeability of the productive formation, economical production is possible only from Wells drilled where stresses have been placed on the productive strata by deep seated folding, or thrust, thus causing natural multiple fracturing of the productive horizon. Numerous wells drilled into the Spraberry formation are not completed as commercial producers due to the fact that the well bore does not intercept the natural fractures within the matrix of the formation. Yet in a large number of these so called dry holes, the matrix of the productive horizon that the bore hole traverses, contains as much available oil in place as do the productive wells, wherein the natural fractures existing in the productive strata contact the well bore. it is estimated that even in the productive wells within the Spraberry formation that in excess of 90% of the oil remains, with present methods, irrecoverably locked in place in the matrix of the formation, and is not recovered by and through the natural fractures existing within this productive horizon.

It is generally understood that tensional, torsional shearing and/ or compressive forces still exist within the matrix of this Spraberry productive formation, as well as other productive horizons of a like nature, that were not relieved by the multiple fractures now existing therein. These forces which are such as would tend to cause fractures, but are of not quite sufficient extent to be relieved by fractures, exist quite extensively in areas of productive strata into which non-productive Wells have been, and are now being drilled.

The natural forces of energy noted above contained within the productive horizons can be utilized along with means to complement, reinforce and/or augment these natural forces. The correct use of abrupt detonation shock forces from explosives placed in advantageous positions in the formation in created fractures, or interfaces of strata adjacent to but apart from the productive horizon, as taught in this invention, will result in the block fracturing of the productive horizon over a considerable area.

A heavy explosive force, used as above, will trigger the looted-in potential forces to at least partially relieve themselves, resulting in a plurality of new fractures and extensions of existing fractures, as well as developing new tensional, torsional, shearing and/ or compressive forces. The multiple fracturing of the matrix of the productive horizon is created by the relieving of these forces to afterward allow the production of fluids from said productive horizon.

By the correct selection of type and amount of nonproductive strata allowed to be between the explosives and the productive horizon, one can control the extent and area of the created fractures so as to produce effective results, rather than expend the explosive force ineffectually in pulverizing and disintegrating the formation adjacent the well bore.

Another beneficial fracturing effect in the present methods using explosives in the formation adjacent to but separated from a productive strata by a portion of non-pr0- ductive strata, wherein natural forces have created fractures, is that by placing the explosives in the formation at the correct location the detonation thereof causes the pro ductive strata to momentarily assume the position it had before the fractures relieved the tensional, torsional shearing and/ or compressive forces that caused the fractures.

These compactual instantaneous shock closures of many of the existing fractures will cause impactual cross, or block, fracturing of the matrix of the productive strata through which these existing fractures cross.

When explosives are used as above, the rarefaction portion of the shock wave following the compressive portion thereof is often more destructive than the compressive portion of the shock wave. The compressive portion of the shock wave will allow the productive formation to spring back to its original position where the natural forces have caused the existing fractures. The reaction of the rarefaction portion of the shock wave will cause the productive strata to assume tensional, torsional shearing and compressive positions far in excess of the natural forces exerted on the productive strata, thus causing additional and extensional fracturing of the productive strata.

It is within the concepts of this invention that explosives may be placed within the formation at positions above and below the productive horizon at points adjacent to but separated from the productive formation by a portion of non-productive strata. These explosions may then be timed so that the compressive force of one explosion will be exerted on one side of the productive horizon when a rarefaction portion of another shock Wave exists therein from said other explosion on the other side of the productive horizon. Explosives may also be placed within the formation above and below the productive strata or two or more explosives may be placed in formation, adjacent to but separated from the productive strata by a portion of non-productive strata, the explosives being apart from each other in the non-productive formation but on one side of the pro-ductive strata, and the detonation of these separate explosives so timed as to each other as to phase angle of shock Wave so as to augment, or reinforce, the explosive force exerted on the productive strata which is adjacent to but spaced from the explosives placed in the formation.

It is also within the concepts of this invention that two or more wells in an oil field may be employed to fracture a productive horizon simultaneously but through different well bores, by the methods herein taught. Where two or more wells are used for the purpose of placing explosives in formation that is adjacent to but separated from the productive horizon by portions of non-productive strata, then detonation of the explosives at the two or more Wells may be at any shock wave phase angle to each other for the purpose of selectively causing the explosive force from each of the wells to combine with the explosive force from the other Well, or wells, so as to cause reinforcement, augmentation or cancellation of the wave energy of the explosively caused shock waves from each of said wells as to each other.

ee /es In some instances it may be desirable to place the explosives in one or more well bores above the productive formation, meanwhile placing the explosives below the production formation in other of the well bores, so as to cause various diaphramic, shock induced, momentary, wrinkle effects to be combined in the productive formation between the well bores, upon detonation of the explosives.

The means specifically used for timed detonating of the different explosives does not form part of the present invention as there are numerous electronic and other known means of timing grouped phase detonations of explosives, such as is employed in pattern detonating of explosives in seismic exploration such as taught in the United States patents to Hasbrook, 2,626,004; Woods, 2,642,146; Flude, 2,283,200; Woods, 2,627,930; Poulter, 2,615,523; Hawkins et al., 2,630,188; or Poulter, 2,672,204, that could be used to provide timed detonations as phase angle co-mingling of shock wave effects of the explosives used in the formation contacted by the well bores.

A rather large proportion of the dry holes or so-called dusters that are drilled as extensions of productive wells at the edge of proven oil and gas fields are dry because the productive horizon is pinched out as to permeability of the pore spaces and/or porosity of formation. These dry holes can often be brought to production by properly following the methods taught herein.

To attempt to cause these above dry wells to become producers by detonating explosives in fractures created within the productive horizon at the well bore would not cause fractures back into the horizon of sufficient extent to contact the productive areas of the horizon, due to the aforesaid localizing of the force of the explosion within an area adjacent the well bore and the pulverizing and disintegrating of the horizon.

The above would be very similar to the now seldom used nitroglycerin shooting of productive formations within well bores which normally causes a pocket or enlargement in the productive horizon near the well bore, except that the detonation of explosives in created fractures within the horizon would cause a considerably larger area of pocket of disintegrated material.

On the other hand, this invention teaches that by the proper selection of type and spacing intervening strata from the horizon to be fractured and amount and type of explosives used, as well as the kind of fluid used and its disposition ahead of the introduction of the explosives, that upon detonation of the explosives deforming and arching of the strata adjacent to but separated from substantially non-deformable and non-compressible horizon by a portion of nonproductive strata is caused over an area in extent such that the fractures therein will contact the productive areas of the horizon and the fractures will be held open sufficiently by the arching and deformation of the adjacent strata for commercial production of fluids at the well bore.

it can be readily seen from the teachings of this invention that a good many of the problems now existing with the use of explosives introduced into crated fractures within the productive horizon, can be eliminated and productive stratas can be fractured by explosives more uniformly and to a far greater extent than has heretofore been possible, and production from the well can be started without the time consuming delays herebefore experienced in the use of explosives within the productive horizon.

Having thus described the preferred embodiments of the invention, it should be understood that numerous modifications thereof may be resorted to without departing from the scope of the appended claims.

What is claimed is:

1. The method of fracturing a productive horizon which includes the steps of fracturing a portion of a formation adjacent to but separated from the productive horizon by a portion of non-productive strata, introducing explosives into the fracture in said portion of a formation, thereafter detonating the explosives to thereby fracture said productive horizon.

2. The method of fracturing a productive strata which includes the steps of introducing explosives into an interface between stratas adjacent a productive strata but spaced therefrom by at least one non-productive strata, thereafter detonating said explosives to thereby fracture said productive strata and subsequently producing fluids from the fractured productive strata.

3. The method of variably controlling the extent and force of explosives used to fracture a producitve oil and gas formation which includes the steps of selecting a strata in a well bore adjacent to but separated from the productive formation by a portion of non-productive strata at a predetermined distance thereto, introducing explosives into a fracture in the selected strata, detonating the explosives, the distance separating the explosives in the strata from the productive formation variably controlling the localized force and extent in area of the fracturing of the productive formation.

4. The method of explosively fracturing a productive strata intercepted by a. plurality of well bores which includes the steps of injecting explosives into formations adjacent to but separated from the productive strata by a portion of non-productive strata from at least two of said well bores, detonating the explosives thereby combining the shock waves in the productive strata between the well bores and thus fracturing the productive strata in order to obtain the production of fluids therefrom.

5. The method as set forth in claim 4 which includes the step of detonating the explosives injected through the separate well bores in timed relation so as to obtain a combining of the shock waves within the productive strata at a selected phase angle of shock wave one to the other.

6. The method as set forth in claim 4 which includes the steps of injecting the explosives into the formation above the productive strata in one of the well bores and below the productive strata in another of the well bores.

7. The method as set forth in claim 4 which includes the steps of injecting the explosives into the formation above the productive strata in one of the well bores and below the productive strata in another of the well bores, and detonating the explosives in timed relation to each other so as to obtain a combining of the shock waves within the productive strata at a selected phase angle of shock wave one to the other.

8. The method of variably controlling the extent and force of explosives used to fracture a productive oil and gas formation which includes the steps of selecting a pair of adjacent stratas in a well bore adjacent to but separated from the productive formation by a portion of nonproductive strata at a predetermined distance thereto, introducing explosives into a fracture in an interface between the selected pair of strata, detonating the explosives, in the interface from the productive formation variably controlling the localized force and extent in area of the fracturing of the productive formation.

9. The method of fracturing a productive strata which includes the steps of introducing explosives into a well bore in an inner face between stratas adjacent the productive strata but spaced therefrom by at least one nonproductive strata, thereafter detonating said explosives to thereby fracture said productive strata and subsequently producing fluids from the fractured productive strata.

10. The method of increasing oil and gas production from a productive strata which includes the steps of forcing a fluid into a well bore in a formation adjacent to but separated from a producing strata by a portion of nonproductive strata in order to fracture the formation, following the fracturing fluid with an explosive material introduced to the fractures in said formation, detonating said explosive material in order to fracture the adjacent productive strata, thereafter producing fluids from the productive strata.

11. A method as set forth in claim 10 wherein the fracturing fluids include a dehydrating additive.

12. The method as set forth in claim 10 which includes the step of following the fracturing fluid with a fluid laden with sand.

13. The method as set forth in claim 10 which includes the step of introducing the explosive material and a fluid laden with sand.

14. The method of fracturing a productive oil and gas strata which includes the steps of fracturing a barren portion of the formation adjacent the productive strata by introducing a fluid into a well bore in the barren formation to create a fracture, withdrawing the fracturing fluid, introducing an explosive into the fracture and thereafter detonating the explosive in order to fracture the adjacent productive strata.

15. The method as set forth in claim 14 which includes the step following the introduction of the fracturing fluid, of introducing a fluid laden with sand, next withdrawing the fluid used to transmit the sand into the created fracture as the fracturing fluid is withdrawn, leaving the sand in the fracture.

16. The method of fracturing a productive oil and gas horizon by the use of explosives which includes the step of introducing explosives into well bores in separate nonproductive stratas adjacent to but separated from a productive horizon by a portion of non-productive strata, both above and below the productive horizon, and detonating the explosives in order to fracture the productive horizon therebetween.

17. The method as set forth in claim 16 which includes the steps of controllably timing the detonations of the explosives Within the separate stratas as to phase the angle of shock wave of each of the explosives to the other for the purpose of obtaining a shock Wave of desired characteristics within the productive horizon.

18. A method of fracturing a productive oil and gas horizon by the use of explosives which includes the steps of introducing explosives into well bores in separate nonproductive stratas adjacent to but separated from a productive horizon by a portion of non-productive stratas, said separate stratas being entirely on one side only of the productive horizon, and detonating the explosives in order to fracture the productive horizon.

19. A method as set forth in claim 18 which includes the steps of controllably timing the detonations of the explosives within the separate stratas as to phase the angle of shock wave of each of the explosives to the other for the purpose of obtaining a shock Wave of desired characteristics within the productive horizon.

References Cited in the file of this patent UNITED STATES PATENTS 2,316,596 Kennedy Apr. 13, 1943 2,368,424 Reistle Ian. 30, 1945 2,547,778 Reistle Apr. 3, 1951 2,699,212 Disrnukes Jan. 11, 1955 2,708,876 Nowak May 24, 1955 2,851,109 Spearow Sept. 9, 1958

Claims

1. THE METHOD OF FRACTURING A PRODUCTIVE HORIZON WHICH INCLUDES THE STEPS OF FRACTURING A PORTION OF A