US3002454A - Method of fracturing earth formations - Google Patents

Description

Oct. 3, 1961 J. D. cHEsNUT 3,002,454

METHOD OF' FRACTURING EARTH FORMATIONS I Filed Dec. 9, 1955 5 sheets-sheet 1 JNVENToR. oH/v 0. @Hfs Ur 'MMR/fx Oct. 3, 1961 J. D. cHEsNUT METHOD OF' FRACTURING EARTH FORMATIONS 5 Sheets-'Sheet 2 Filed Dec. 9, 1955 INVENTOR.

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METHOD OF FRACTURING EARTH FORMATIONS 5 Sheets-Sheet 3 Filed Deo. 9, 1955 INVENTOR.

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3,002,454 METHOD F FRACTURN G EARTH FORMATIONS John D. Chesnut, Newport Beach, Calif., assigner to Aero jet-General Corporation, Azusa, Calif., a corporation of Ohio 'Filed Dec. 9, 1955, Ser. No. 552,150 `8 Claims. (Ci. IGZ- 21) This invention relates to means for increasing the rate of iiow or oil from oil wells. More particularly, the inven,` tion relates to a Amethod of increasing the vertical permeability of laterally disposed oil well drain holes by means of Van explosive method of fracturing the oil-producing formation.

It is well that most oil-producing formations produce oil by movement of the oil along the bedding planes of the earth formation. Since these bedding planes are formed by sedimentary deposits, they are approximately horizontal (as opposed to vertical) with respect to the usual vertical well bore. The permeability of an oil sand may be high in a lateral direction away from the main, vertical, bore of the well, and at the same time be low or non-existent in a vertical direction. This dierence in permeability between lateral and vertical ow results from the fact that oil stands, as originally laid down, were sedimentary in character and were covered by successive layers of impervious deposits.

Since the rate of production of oil from an oil sand .is more or less proportional to the thickness of the sand (other things being equal) it is obvious that a thin sand will produce oil Yat a low rate, in barrels per day, as compared to a thicker sand.

it has been proposed heretofore to increase the produc tion of oil yfrom their sands or from the less permeable sands, by drilling one or more drain holes extending laterally from the main bore of the Well. 1n some instances tmc procedure has resulted in substantial increases in production while in other instances there has been little-Orino increase Yin production. t

it is believed that in those cases where little or no increase in production was obtained, even though the oil sand showed good permeability and saturation, the failure to increase production was due inpart to the lack of sufiicient vertical permeability to permit the entire thickness of the oil sand to be drained. Attempts to increase production .from such wells -by means of several well known hydraulic .fracturing methods have been unsuccessful, probably because vany fracturing occurred along the hon'- aontal bedding planes without increasing the vertical permeability.

The principal object of the present invention is to provide explosive -means for increasing the vertical permeability of oil sands in which lateral drain holes have been drilled.`

Another object is to provide means for loading successive drain holes with explosive.

. Another object is to provide means for detonating explosive 'bodiessituated in one or more lateral drain holes.

Another object is to provide means for protecting the lateral drain holes and/or the main bore of the Well against 'collapse due to the force of the explosive detona tion.

FIG. l is 'a vertical cross section of a well having a series of lateral drain holes, previously drilled, in the process ofbeing loaded with liquid explosive;

FlG. 2 is a vertical cross section of the well shown in IG. l in the ready-to-re condition;

FIG. 3 is a vertical cross section of the wall shown in FIG. l after the explosive has been tired;

FIG. 4 is a vertical cross section of a Well similar to #that shown in FIG. .l but illustrating two alternative methiaten'ted Oct. 3, i961 ods of loading the lateral drain holes with -a liquid explosive; and

FIG. 5 is a schematic view showing a method of detonating archarge of explosive by cable meansV controlled from the top of the well and extending downward into the well.

Referring to FIG. l, a substantially vertical well bore is indicated at l'haviug a casing 2 cemented therein as indicated at 3. Non-oil-bearing earth formation is indicated at 4, both above vand below an oil-bearing formation 5. The oil-bearing formation 5 is interspersed with substantially horizontal, impermeable layers of earth formation as indicated at 6, dividing the permeable zones 5 into several layers.

The well bore 1 may be bottomed in the .non-oil-beaning zone, as shown in FIG. l, or in the oil bearing zone.

The well casing 2 may be cemented from top to bottom as indicated at 3 or it may be cemented only in the upper portion of the well as indicated at 3a.

The casing .2 may or may not be perforated as ,indicated at 7 opposite the oil producing zones. A pair of lateral drain holes S, 9 .are shown as having been drilled through the casing 'Z and cement 3 into the oil producing zone 5 in substantiallyy horizontal directions. Any desired number of such lateral drain holes may -be drilled in the Well known manner. The-drain holes may all be at the same level in the well, or they may be at different levels, as shown in EIG, 1,.

The well bore and'casing contain well iiuid (oil, water or mud) which may have a standing level near the top .of the wellas indicated at 10, or at some point lower down in the well.I

After the lateral drain holes 8, 9 have been drilled, a whipstock '11 is um Vinto the well. rihe whipstock 1i is mounted on avspacer or standpipe 12 having a fo-otpiece 13 which is positionedeccentrically to the vertical axis of Va casing shoe 14 which has a mating recess 15 formed therein. The whipstock 11 may be the same whipstock which was employed during the drilling of the drain hole S, in which event, it will be oriented automatically to the position shown in FIG. '1, because of alignment o'f the eccentric recess '15 and the mating footpiece 13, to direct any descending tools Vor other objects into the drain hole.

Gne or moretubnlar containers 16, which may or may not be ilexible, 'are vshown as being detachably supported on 'a length offilexible tubing 17 attached to the lower end of a string of tubinggi which extends to the top of the well. A 'bayonet type-coupling 19 may be used asfthe detachable coupling.

The tubular container 16 vcontains an explosive charge and one or more detonators 20. The detonators Ztlmazy be Vactuated by any one of vseveral means such as a time bomb, a 'pressure-sensitive switch, an electrical switch or a mechanical percussion device, as will be more fully described.

The tubular containers' 16 are employed when it is desired 'to prevent Contact between the explosive charge and the AWell Huid. The A'containers may be made of vari- 'ons materials such as polyethylene or other plastics, rubber,'tin, 'aluminum-or the like. The walls of the container maybe thick 'or thin depending upon the service conditions Aand the type 'of explosive used.

After the lowermost drain hole 8 has been loaded with explosive, vthetubing 17, 18 and the whipstock 11are-re moved from the well. The standpipe 12 is replaced with a longer standpipe which will enable the whipstock body 11 to come to rest opposite the entrance to the upper drain hole 9, provided the body 11 and footpiece 13 'are assembled in properly oriented position. lf the drain holes 8 and 9 are on the vsame level, it is only necessary to re-orient the body 11 on the standpipe 12 before vrunning theWhipStock back into the well. The upper V.or

other drain holes are then loadedwith explosive in a similar manner and the tubing 17, 18 is removed from the well, which is now ready for ring as shown in PIG. 2.

The ring means shown in FIG. -Zicomprises a pressure-sensitive detonator 21 located in each of the tubular explosive containers 16. A bridging plug 36 is positioned in the well fluid adjacent the drain holes 8 9. The Vbridging plug may contain a time bomb 22 or a pressure sensitive detonator. If a time bomb is used, the shock wave emanating therefrom and traveling through the Well uid Will set oit the pressure-sensitive detonators 21 which will detonate the explosive charges in the containers 16. If the time bomb 22 is replaced by a pressure-sensitive detonator, it is necessary to employ additional means for creating pressure in order to actuate the pressure-sensitive device. Suchmeans mayinclude uid pressurizing means such as a pump 23 or ari-explosive body 24 suspended on an electric cable 25.

FIG. 3 illustrates the condition of the Wellv shown in FIGS. l and 2 after detonation of the explosive charges 16. A large number of cracks and fissures 27 radiate outwardly from the drain holes 8 9, and provide channels through which oil from the various layers of the oil bearing formation can enter the drain holes 8 9 and pass into the main Well bore 1. 'Since some of the cracks and iissures 27 will intersect the impermeable layers 6, a vertical permeability will be createdV throughout the oil bearing formation 5. FlG. 4 illustrates another embodiment of the invention vvhe'rein the explosive is a liquid which lls thelateral drain holes 8 9 and alsoV iills a part ofthe Well bore 1 or well casing 2. In order that this system can be used, it is necessary that the explosive be a liquid or a plastic material, also, that the explosive does not react with or become soluble in the Well iiuid, and that the earth formation 5 does not permit the explosive to escape from the drain holes 8 9 before detonation takes place. Whether or not the Well is cased, it may be desirable in some instances, to protect the well casing 2 and/or the drain holes 8 9 against collapse from the effects of the detonation. This can be accomplished by filling the drain holes and Well casing with coarse gravel, or the like, as indicated at 28. The presence of the gravel 28 not only reinforces the casing 2 and well bore 1 against collapse, v`but also serves t0 reduce the volume of explosive required to fill the drain holes and main well bore. The volume of explosive required can be still further reduced by placing a plug or packer 29 in the main bore or casing just below the lowermost drain hole S. The plug and gravel can be drilled up and circulated out of the well after the well has been shot. Y l

FIG. 4 also illustrates alternative means for detonating the explosive charge. A time bomb 30 is shown positioned in drain hole 8 and a pressure-sensitive detonator 31 is shown in drain hole 9. Detonatorl is iired by the shock wave emanating from the time bomb 30.

FIG. 4 also illustrates another method of operation wherein the drain hole 9 is shown as being only partially lled with liquid explosive, the top of the explosive column being indicated at 32 located at some distance away from the Vmain bore hole 1, in order to protect the main bore hole against collapse from the detonation shock. Well fluid above the surface 32 of the explosive serves as a tzunp and also as a means for transmitting the shock wave from the time bomb 30 to thepressure-sensitive detonator 3i. it is obvious that various other types of letonators can be substituted for the detonators 30-31 Without departing from the spirit of the invention.

YSince the explosive employed in FIG. 4 is a liquid it may be pumped into the drain holes 8 9 through the tubing 17-18 (FIG. l). If'the explosive liquid is of greater specific gravity than thevvvell iiuid and does not react with or become soluble in the well fluid, it will displace an equal volume of Well fluid in the drain holes 8 9 and/or the main bore hole 1. In this case the containers 16 may be omitted. An example of such a liquid explosive is nitromethane to which has been added a sensitizer, such as an amine of the type described in the copending application of Edgar A. Laurence, Serial No. 605,747, filed July 18, 1945, and assigned to the same assignee as the present application.

FIG. 5 lustrates still another method of detonating the explosive charges 16a by means of pressure-sensitive detonators Zia located in the explosive charges 16a, and actuated by a shock Wave from an explosive body 24a suspended in the Well uid from a line 25a extending to the top of the Well. The explosive body 24a may be of any desired type.

The initiator 24a may be detonated by various means, such as by electric energy sent through the suspension line 25a. Or, if an insulated electric line isnot available, a steel cable may be used, together With a go-devil weight 33 which surrounds the line 25a and is dropped from the top of the well. In this case the initiator 24a is provided with a ring pin 34 which is actuated by contact with the go-devil 33. The firing means which is actuated by movement of the tiring pin 34 may be either mechanical or electrical. If electrical, a battery or other source of electric current must be used.

It is to be understood that, in addition to filling the drain holes 9 with liquid explosive, such explosive can also be forced into the oil producing formation 5 by the application of pressure to the column of liquid Within the well casing 2. This can be accomplished in the conventional manner by applying pump pressure to the liquid column at a pressure high enough to force a part of the liquid explosive in the oil bearing formation 5 While leaving a part of the explosive liquid in the drain hole 9 in contact with the detonating device 30. The advantage of such a method is that the effective length of the drain holes 9 is increarsed materially Without the need for a diiiicult and expensive drilling job.

It is to be understood that the methods and apparatus described herein are illustrative only, and that the invention is not limited thereto but is of the scope defined by the appended claims.

I claim:

l. A method of fracturing earth formations in wells having a main bore hole provided with one or more drain holes extending laterally therefrom and containing a Well iiuid, comprising: iilling said drain holes with coarse gravel or the like to prevent collapse of the Awalls of said drain holes, placing a body of sensitized ntromethane explosive in one or more of said drain holes to iill the interstices among the gravel, said sensitized nitromethane explosive body containing a detonator of thepressuresensitive type, and applying pressure to said well uid suthcient to actuate said pressure-sensitive detonator whereby said sensitized nitromethane explosive body is detonated within said one ormore of said drain holes.

2. A method of fracturing earth formation in wells having a main bore hole provided with one or more drain holes extending laterally therefrom and containing well duid, comprising: iilling said drain holes and said main bore hole with coarse gravel or the like, placing a body of sensitized nitromethane explosive in one or more of said drain holes and said main bore hole to `till the intersticcs among the gravel, said gravel functioning to prevent collapse of the walls of said drain holes and said main bore and reduce the amount of explosive required, said sensitized nitromethane explosive body containing. a detonator of the pressure-sensitive type, and applying pressure to said Well uid sufhcient to actuate said pressuresensitive detonator whereby said sensitized nitromethane explosive -body is detonated within said one or more of said drain holes.

3. A method of fracturing earthformations in wells having Ia main bore hole provided with one or more drain holes extending laterally therefrom and containing well fluid, comprising: placing a body of sensitized nitromethane explosive in one or more of said drain holes, said sensitized nitromethane explosive body containing a detonator of the pressure-sensitive type, and l'applying pressure to said well iluid suicient to actuate said pressure-sensitive detonator by detonating an explosive body positioned in said main bore hole, whereby said sensitized nitromethane explosive body is detonated Within said one or more of said drain holes.

4. A method of fracturing earth formations in wells having a main bore hole provided with one or more drain holes extending laterally therefrom and containing well uid, comprising: placing a body of sensitized nitromethane explosive lin one or more of said drain holes, said sensitized nitromethane explosive body containing a detonator of the pressure-sensitive type, placing a pressure-sensitive detonator in the main bore hole in a bridging plug positioned below the uid level in the well, and applying pressure to said well uid suiiicient to actuate said bridging plug pressure-sensitive detonator whereby said sensitized nitromethane explosive body is detonated within said one or more of said drain holes.

5. A method of 4fracturing earth rior-mations in wells having a main bore hole provided with one or more drain holes extending laterally therefrom and containing well iiuid, comprising: lling said drain holes with coarse gravel or the like to prevent collapse of the walls of said drain holes, placing a body of sensitized nitromethane explosive in one or more of said drain holes to lill the interstices among the gravel, said sensitized nitromethane explosive body containing a detonator of the pressuresensitive type, land applying pressure to said Well fluid sufiicient to actuate said pressure-sensitive detonator by detonating an explosive body in said main bore hole whereby said sensitized nitromethane explosive body is detonated within said one or more of said drain holes.

v6. A method of racturing earth formation in Wells having a main bore hole provided with one or more drain holes extending laterally therefrom vand containing Well iiuid, comprising: iillin-g said drain holes `and said main bore hole with coarse -gravel or the like, placing a body of sensitized nitromethane explosive in one or more of said drain holes and said main bore hole to ll the interstices among the gravel, said gravel lfunctioning to prevent collapse of the walls of said drain holes Iand said main bore and reduce the amount of explosive required, said sensitized nitromethane explosive body containing a detonator of the pressure-sensitive type, and applying pressure to said well ilu-id -suiiicient to actuate said pressure-sensitive detonator by detonating an explosive body gravel or the like to prevent collapse of the walls of said drain holes, placing a body of sensitized nitromethane explosive in one or more of said drain holes to ll the interstices among the gravel, said sensitized nitromethane explosive body containing a detonator of the pressuresensitive type, and applying pressure to said well uid suiiicient to actuate said pressuressensitive detonator by Y detonating an explosive body in said main bore hole, said explosive body comprising a detonator Aarranged in a bridging plug positioned below the iiuid level in the well, whereby said sensitized nitromethane explosive body is detonated said one or more of said drain holes.

8.V A method of 'fr-acturing earth formation in wells having a main bore hole provided 'with one or more drain holes extending laterally therefrom and containing well fluid, comprising: lfilling said drain holes and said main bore hole with coarse gravel or the like, placing a body of sensitized nitromethane explosive in one or more of said drain holes and said main bore hole to iill the interstices among the gravel, said gravel 'functioning to prevent collapse of the walls of said drain holes and said main bore and reduce the amount of explosive required, said sensitized nitrofmethane explosive body containing a detonator of the pressure-sensitive type, and applying pressure to said well fluid sucient to actuate said pressure-sensitive detonator by detonating an explosive body in said main bore hole, said explosive body comprising a detonator arranged in a bridging plug positioned below the iluid level in the well, whereby said sensitized nitromethane explosive body is detonated said one or more of said drain holes.

References Cited in the lile of this patent UNITED STATES PATENTS 86,691 Roberts Feb. 9, 1869 316,137 Gallagher Apr. 2l, 1885 1,979,802 Kinley Nov. 6, 1934 2,171,416 Lee Aug. 29, 1939 2,304,408 Holitield Dec. 8, 1942 2,316,596 Kennedy Apr. 13, 1943 2,749,840 Babcock June 12, 1956 2,892,405 Chestnut June 30, 1959 FOREIGN PATENTS 367,858 Great Britain Feb. 26, 1932

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