US3066734A - Method of vertically fracturing wells - Google Patents

Description

Dec. 4, 1962 R. F. MEIKLEJOHN METHOD OF VERTICALLY FRACTURING WELLS 3 Sheets-Sheet 1 Filed April 11, 1957 J I &. 1.

IN VEN TOR. 2054527" r? 4494 45/04 Dec. 4, 1962 R. F. MEIKLEJOHN 3,066,734

METHOD OF VERTICALLY FRACTURING WELLS Filed April 11, 1957 5 Sheets-$heet s Fla. 5.

INVENTOR. Easier A J/ET/KAE/QZ/A/ ezwv FIG. irrae/viy United States Patent Office Patented Dec. 4%, 1962 3,066,734 METHOD 6F VERTICALLY FRAQTURING WELLS Robert F. Meiidejohn, Los Angeies, (Iaiifi, assignor to B 8 Service, Inc, Long Beach, Calif, a corporation of Delaware Filed Apr. 11, 1957, Ser. No. 652,154 1 Claim. (Cl. 166-42) The present invention relates to an improved well treating method.

In the field of treating oil and gas wells, it frequently becomes desirable to inject fluid down into the well for treating the earth formation traversed by the well as in formation fracturing, acidizing, cleaning and other fluid operations, as well as in cementing or the like. Relatively high fluid pressures and/ or injection rates are often required in order for the treatment to be effective. Despite the availability of pump pressure at the well head, adequate downhole pressures are oftentimes diflicult to attain because of friction losses, depending upon the viscosity of the treating fluid, whether the fluid is being pumped down tubing or down casing, into an open hole or into the formation through casing perforations, and other factors.

In fracturing earth formation to enhance the flow of oil into the well from relatively impermeable strata or to provide communication between the well and blocked oil bearing strata or sands to enable production thereof, fluid is pumped into the well under pressure for overcoming the stresses of adjacent tight or impermeable strata to form fissures or cracks radiating from the well, such cracks resulting from actual fracturing of rock or shale formations, or the like, having a yield point at which they will rupture responsive to internal tension. In the case of formations having existing tight fractures, the fracturing fluid merely overcomes the confining stress and opens the existing fractures, such as exist at boundries or the bed planes of different strata. Higher pressures are required to effect actual fracturing of the rock or other formation than are required for o ening existing fractures, whereas lower viscosity fluids and higher in- "ection rates are generally required in the latter case.

Depending upon the rate of loss of fluid into the formation, the depth of the well, and the viscous properties of a fracturing or other treating fluid, as well as upon the capacity of the surface pumps to provide high injection rates and/or pressures, suificient pressures and/or injection rates may at times be practically unattainable. Means for and a method of providing a single-stroke pump-like boost to the fluid pressure to implement available surface pump pressure are disclosed in the co-pending patent application of Lyle B. Scott and Mathew B. Riordan, Jr., filed October 16, 1956, Serial No. 616,333, for Well Treating Method and Apparatus, and now abandoned.

According to the invention of that application, a container of low-propellant ,or rocket-type fuel is disposed in the well adjacent to, or just above, the producing or potentially productive Zone to be fractured or otherwise treated. Without interrupting the flow of fluid from the surface pumps, the propellant is ignited or detonated so as to produce a large volume of ga pressure which is, so to speak, super-imposed upon the pump pressure to provide a powerful boost or assist to the effective pressure of the treating fluid, which in a fracturing operation may be required to lift the ovcrburn at the zone of fracture. Such overburden of ordinary sedimentary formation applies a vertical stress of approximately 1.0 p.s.i. per foot of depth, although this may vary due to the overlying weight of some strata being borne by a bridging action caused by earth movements. Therefore, in relatively deep wells, substantial pressures must be developed in order to effect fracturing.

The detonation or ignition of the propellant or rocket fuel charge aforementioned is adapted to supply, in addition to the pump pressure which may be inadequate for efiective fracturing, a pulse -like pressure boost of thousands of pounds, thus enabling initial opening of the formation by the creation of new or opening of old fractures. Following such initial opening, continued pump pressure is adequate to open the formation further, so that fractures radiating from the well may be of substantial extent, depending upon the differences in stress between adjacent formations through which the fractures extend and the borehole wall being fractured. Such fractures may extend radially of the well upwards of 1,000 feet and more.

An object of the invention is to provide a method of producing vertical fractures in the earth formation traversed by a well bore, it being intended that the term vertical as employed herein contemplates fractures which are not necessarily truly vertical, but which may be disposed at a substantial angle relative to a vertical plane.

In wells where the tensile strength of the surrounding formation is high and vertical compressive strengths are low, pressure fluid will leak off into bedding planes or high permeability sections and will help to start so-called horizontal fractures. When native fractures exist, a stress wedge is provided by the pressure fluid which will open the native fractures at a pressure which may be less than the least stress in the surrounding formation. If such native fractures and high permeability areas are sealed oif, thus causing uniform pressure distribution around the hole, initial fracture will occur in a line following the pattern where rock or formation tensile strength is lowest. Such fractures will usually be vertical, or at least nearly so, but may, depending upon varying formation strength characteristics, vary to the point of being nearly horizontal.

The method of this invention contemplates sealing off native fractures and high permeability areas in the formation so as to avoid the formation of stress wedges and the initiating of fractures in these areas, the result of such sealing being that subsequent application of fracturing pressure will effect fracturing at the line of least resistance which may differ from the area in which the native cracks or fractures and high permeability areas are located.

A further object of the invention, then, is to provide a method of fracturing an earth formation which is traversed by a well, which comprises pumping into the well a low fluid-loss fracturing fluid preferably having lost circulation material therein for forming a substantially fluid-impervious cake about the borehole Wall, applying fluid pressure uniformly about the bore wall, and fracturin the formation in the area of the least stress or resistance to fracturing by the application of a shock of fracturing pressure, and continuing the pumping of fluid into the formation.

A still further object is to provide a method of fracturing earth formation traversed by a well which comprises: disposing a container of gas-generating material in the well adjacent to or above the formation to be fractured; injectin a low fluid-loss fracturing fluid into the well and forming a fluid impervious layer or cake about the surface of the formation to be fractured; building up pressure in said well to a pressure below the incipient breakdown pressure; halting such pressure buildup; and then simultaneously resuming fluid injection and initiating detonation of said gas'generating material and providing therewith a surge of fracturing pressure augmenting the pressure provided by the fluid injection; and fracturing said formation in the Zone of least resistance while continuing the injection of fluid into the well.

Other objects and advantages of the invention will be hereinafter defined or will become apparent to those skilled in the art, and the novel features thereof will be defined in the appended claim.

The method hereof may more readily be understood when described in relation to apparatus which is ideally suited to perform the method. Such a tool or apparatus is illustrated in the accompanying drawings, wherein:

FIG. 1 is a fragmentary view partly in elevation and partly in vertical section of well head apparatus for use in the performance of the instant method, with the apparatus illustrated at the earth surface above a well;

FIG. 2 is a downhole continuation of the apparatus of FIG. 1, showing propellant booster means disposed in the well above earth formation to be fractured;

FIG. 3 is an enlarged fragmentary view in vertical section through the firing head of the booster means of FIG. 2, with the parts shown in a normal non-firing position;

FIG. 4 is a view similar to Fit). 3, but showing the parts in a firing position; and

FIG. 5 is an enlarged fragmentary view in longitudinal section showing certain of the firing head parts of 1 16. 4 in elevation.

Referring now to the drawings, and particularly to FIGS. 1 and 2, a particular utilization of the method is illustrated together with apparatus which is particularly adapted to the performance of the method. The apparatus is the subject matter of a co-pending application of Lyle B. Scott, Serial No. 652,286, filed of even date here with and now Patent No. 3,001,584.

A well generally designated W is shown as drilled 01' extending into a productive or potentially productive formation F, with well casing C extending to a level adjacent to the upper boundary of the formation F and cemented in place as is customary. A tubing tring T is suspended in the well by means of conventional well-head equipment shown schematically at H, with the lower extremity of the tubing terminating with a bull plug or closure D in subjacent relation to the lower extremity of the tubing. The lower end of the tubing comprises a slotted section affording fluid intercommunication between the tubing and the open hole beneath the casing. A suitable packer P is interposed between the tubing and the casing.

At the surface, the tubing is provided with a lubricator assembly L to which is connected a valve manifold M having valves V and V for controlling the injection of fluid into the lubricator at points either above or below a plug release device R which is fluid operated to retain or release for injection into the tubing a ball B. The details of such a ball releasing device are disclosed in the copending application of Lyle B. Scott, filed April 11, 1958, Serial No. 727,826.

The formation F beneath the casing T is shown as having a number of native fractures radiating from the open hole. However, in accordance with the invention, a filter cake Y is shown as deposited upon the wall of the open hole so as to seal the native fractures and other permeable areas to prevent the loss of fluid into the formation F.

Apparatus X is interposed in the tubing string T for containing and firing a low propellant booster charge. This apparatus generally comprises a firing head section 1 and a lower propellant-containing chamber or receptacle 2. The firing head is adapted for connection in such tubing string T as by means of a tool joint 3, the propellant container or compartment 2 being adapted for connection in the tubing string as by means of a coupling or tool joint 4.

Otherwise, the assembly includes an elongated orifice tube having an upper firing head section 6 and a lower propellant-container section 7, these tube sections 6 and 7 being threadedly interconnected with one another as at 8 and being concentrically disposed within coaxially extended firing head and propellant container cases 9 and it respectively. Adjacent to its lower end, the orifice tube section 6 is provided with a radially projecting adapter flange 11 against which the upper extremity of the firing head case 1% abuts, with the case it) held in tight abutting contact with the flange 11 by an interiorly threaded sleeve 12, threadedly engaged with the case 10 and having a radially, inwardly projecting, flange 13 en gaged with the flange 11. The firing head case 9 abuts with the flange 13 at the lower extremity of the case and is retained in position by means of a threaded nut 14 engaged with the threaded outer periphery of the orifice tube section '5 at the upper end of the firing head case 9. A spacer ring 16 is preferably disposed between the case and the upper extremity of the orifice tube section 6 and welded to the firing head case as at 17.

Suitable sealing means such as a sealing ring 18 interposed between the spacer ring 16 and the orifice tube section 6, a sealing ring 19 interposed between the upper extremity of the propellant compartment case 10 and the orifice tube section 6, and a sealing ring 20 disposed at the base of the propellant chamber are provided for sealing the firing head and the propellant compartment against the entry of well fluids. The sealing ring 29 (see FIG. 2) is interposed between an adapter sleeve 21, which is suitably mounted upon the exterior of the orifice tube section '7, and a spacer ring 22 interposed between the sleeve 2 and the case 10 and preferably welded or otherwise suitably secured to the latter as at 23. A lock nut 24 threadedly engaged with the sleeve 21 aids in retaining the case 10 in place.

The propellant container 2 has disposed therein a quantity of gas-generating material, and without departing from the invention, such gas-generating material may be any of a number of divers types, either liquid or solid. But for illustrative purposes, strips of a solid propellant material generally designated 25 are shown interposed in the annular space between the case 10 and the orifice tube section 7, with a firing strip 26 interposed between the propellant strips 25 and the orifice tube section 7, and with an ignitor strip or ring 27 encircling the orifice tube section 7 between the propellant strips 25 and suitable firing mechanism which will be hereinafter more particularly described.

The propellant itself may, when a solid propellant such as herein disclosed is employed, consist of a slow burning propellant such as rubberized ammonium nitrate or the like. Such a solid propellant may be obtained, for example, from Grand Central Rocket Company, Mentone, California, under their designations CBS-128K" or CBS-128H. Alternatively, it may consist of ordinary railroad fusee material, such as saw dust impregnated with sodium or ammonium nitrate, or it may consist of one of a variety of rocket fuels. Suitable propellants are described by T. L. Davis in Chemistry of Powder and Explosives, 1943, John Wiley & Son, publishers. As is well known, these solid propellants may vary in their composition so as to burn at varying rates, but when employed in the present invention, a burning time of on the order of about ten seconds is preferable. Such burning of the propellant material will result in the generation of a high volume of gas Within the sealed annular space between the case 10 and the orifice tube section 7.

A suitable number of gas relief plugs 28 are threadedly mounted in the orifice tube section 6, these relief plugs each having an orifice 29 therethrough sealed by means of a frangible disc 30 which, when subjected to high internal gas pressures, will rupture and allow the escape of gas.

from the gas chamber between the case 10 and the orifice tube 7 into the passage through the latter. The result;

of the generation of such gas and escape thereof through ensured the orifice tube will be more particularly described hereinafter.

Within the case 9 is suitable means for effecting firing or detonation of the propellant material, and more particularly, the ignitor strip 27. To this end, a suitable number of axially extended openings are formed through a radial orifice tube enlargement 31 from which the adapter flange 11 projects, these openings being designated 32 and each having disposed therein a blank cartridge 33. The orifice tube section 6 is provided with a peripheral groove or channel 34 in which is disposed an annular breech block 35.

Shiftably mounted in the breech block 35 and disposed for engagement with the blank cartridges 333, is a like number of firing pins 38 which, upon receiving a sharp percussive blow, will fire the blank cartridges, thus in turn igniting or firing the propellant material. The means for providing such a percussive blow to the firing pins 38 includes an annular hammer 39 disposed between the orifice tube section 6 and the firing head case 9. At opposite sides-thereof, the hammer 39 is preferably provided with a pair of generally L-shaped slots it), with a like number of pins 41 threadedly fixed to the orifice tube section 6 and projecting into the slots 40, so that when the pins 41 are disposed in the off-set base portions of the L-shaped slots 49, the hammer 39 will be retained against axial shifting movements, whereas upon slight rotative movement of the annular hammer 3& the elongated portions of the slots it) will enable axial movement of the hammer 39 into engagement with the firing pins 38.

An axially extended operator member 42 is slidably mounted upon the outer periphery of the orifice tube section 6, this actuator member 42 having a radially, outwardly, projecting flange or shoulder 43 thereon, disposed in opposed spaced relation to the upper extremity of the annular hammer 39. A coiled spring 44 is disposed between the shoulder 43 and the latter end of the hammer 39 so as to normally bias the hammer towards the firing pins 38. Means are provided for shifting the actuator member 42. axially, such means including an actuator sleeve 45 slidably mounted within the orifice tube section 6. A number of axially extended slots 46 are formed in the orifice tube section 6, and a number of lugs 47 project through the slots as and are connected to the upper extremity of the actuator member 42 as by means of a suitable number of screw fasteners 48, these lugs 47 being seated in an annular groove 49 in the outer periphery of the actuator sleeve 45 so that the actuator member 42 and the sleeve & are moveable axially as a unit.

Referring particularly to FIG. 5, the hammer 39 is provided with a pair of radially, inwardly projecting, pins 59 and 51, these pins being spaced from one another both in an axial direction and in a circumferential direction with relation to the hammer 39. The pin 51 is adapted to cooperate with an inclined cam surface 51 on the actuator member 42 so that upon engagement by the pin 51 responsive to axial movement of the actuator member 42, the hammer 39 will cam rotatively in a direction to unseat the pins 41 from the bases of the L-shaped slots 4%, thus freeing the hammer 39 for axial movement responsive to the pressure applied thereto by the spring 4 4. The actuator member is provided with a longitudinaily extended slot 5t? having a cam surface 5d" engageable with the pin 51), so that axial movement of the hammer 39 in the opposite direction will effect camming of the hammer 39 rotatively in a direction whereby the pins 41 are moved into the bases of the slots as.

The structure thus far described is merely illustrative of a construction which is particularly adapted for use in connection with the performance of the method here of and is described in particular detail in the copending application of Scott and Riordan, 11'. previously referred to. illustratively, it is to be understood that the impact producing hammer means may, if desired, be of the type 6 disclosed in the copending of Lyle B. Scott, Serial No. 638,375, filed February 5, 1957 for Firing Head for Formation Treating Apparatus.

However, as had been hereinbefore pointed out, the method hereof particularly concerns the performance of vertical fracturing; that is, fracturing the earth formation by overcoming the lateral or horizontal stresses in the surrounding earth formation as distinguished from longitudinai or vertical compressive stresses.

Accordingly, the actuator sleeve 45 is provided with an annular seat member 52 at its base, and extending upwardly in the sleeve 45 from closely adjacent the seat 52 is a plurality of circumferentially spaced by-pass orifices or openings 53. Preferably these orifices 53 are of such a size and configuration that their overall area ieast equal to or greater than the opening through he seat 52 Formed in the inner periphery of the orifice ube section 6 is an annular by-pass chamber 5% so that hen tr e openings 53 of the sleeve 45 register with the y-pass chamber 54, fluid passing downwardly through he sleeve 45 will flow through the orifices 53 and the y-pass chamber and thence on through the orifice ube sections .6 and '7. The outer periphery of the .nnular member 52- is preferably of a slightly smaller diameter than the inside diameter of the orifice tube section 6, so that a limited fluid flow is permitted past the member 52 to preventsand clogging in certain fracturing operations where sand or some other propping agent is employed in the fluid.

However, when the operator sleeve 4-5 is in the position shown in FIG. 2, where it is normally maintained by the pressure of the spring .4, the orifices or openings 53 in the sleeve 45 wiil be closed off by the inner periphery of the orifice tube section 6 so that fluid passing downwardly through the sleeve 45 will flow through the seat 5'2 until such time as a check valve or the like engages with said seat 52 to deter such flow. Such a c'ieck valve is herein shown as being constituted by a ball B which has a diameter slightly greater than the seat 52, but which is of such a size as to freely pass downwardly through the sleeve 45 into engagement with the seat 52.

As the ball 13 passes down through the tubing into engagement with the seat 52, the further free flow of fluid through the sleeve 45 will be prevented or minimized. Therefore, continued operation of the surface pumps, as is customary, will force the sleeve 45 downwardly until the fiuid is free to pass through the orifices 53 and into the by-pass chamber 54, thus resulting in firing of the blank cartridges 33. If desired, the ball B may be composed of a soft material such as aluminum or a deformable plastic material such as nylon so that in the event of blockage of the by-pass orifices 53, a build-up of pressure behind the ball B within the sleeve 45 will extrude the ball through the seat in the performance of the method hereof with the apparatus described above, fluid will be injected into the well throu h valve V while valve V is closed, into the tubing string T. In a vertical fracturing operation, such fluid will preferably be of a so-called low-fluid-loss type; that is, of a type consisting of a gelled hydrocarbon such as kerosene or gasoline having a relatively high viscosity, but having the characteristic of not materially retarding the injection rate by virtue of the increase in visddsity due to gelling. In addition, the fluid preferably will include a suitable wel -known fluidloss-preventing material which will form the filter cake Y upon the wall of the borehole in those areas where fluid tends to flow out into the formation. Such fluid will be pumped down into the hole until such time as the pumps may be halted and pressure retained in the well. Indeed, it may require building up in increments to an internal pressure in the well just below the incipient breakdown pressure of the formation to be fractured; that is, the well will be pressurized up to a point and the pumps shut down to determine whether the pressure will hold. And such operation may be repeated until the well will hold the desired pressure.

With the surface pumps halted, the ball valve B may then be injected into the well without relieving the pressure upon operation of the ball release means R, and allowed to settle down in the tubing until it rests upon the seat 52, thus precluding free flow of fluid through the firing head whereupon recommencement of the pumps will exert a pressure upon the ball, thereby moving the actuator sleeve 45 downwardly. Such movement of the actuator sleeve will effect a corresponding downward movement of the member 42 with the result that the cam surface 51' thereon engaging with the pin 51 will effect rotation of the hammer 39 until the pins 4t are released from the off-set bases of the slots 40 and the spring 44 forces the hammer 39 into contact with the firing pins 38. Thus, the cartridges 35 will be fired, the propellant or rocket fuel ignited or detonated, and a high volume of gas will be generated in the annular space between the orifice tube section 7 and the propellant-container case 10. The frangible discs 39 will accordingly be blown out by the gas pressure and the gas will escape into the orifice tube section 7 and exert a sudden impulse of high pressure on the fluid therebeneath with the result that the earth formation will be fractured. Since the low-fluidloss characteristics of the fracturing fluid and the fluidloss-preventing material therein will prevent the flow-off of fluid into the formation through native fractures or through porous areas of high permeability, no pressure wedges will be forced off into the formation such as would ordinarily tend to produce a horizontal fracture. Instead a pressure is produced which surpasses the tensile strength of the borehole, overcoming the tangential opposing forces and fracturing the earth formation at the point where the tensile strength is the lowest, this type of fracture generally being referred to as a vertical fracture, though it may indeed be disposed other than vertically.

Continued pumping of fluid downhole during and following detonation of the propellant or rocket fuel will tend to enlarge the fracture or fractures after they have been initially formed.

While the specific details of the method hereof have been specifically described, changes and alterations may be resorted to without departing from the spirit of the invention as defined in the appended claim.

I claim:

The method of fracturing earth formation traversed by a well bore, comprising running into said Well bore a string of conductor tubing having therein a container of gas generating material capable of generating a surge of gas pressure upon ignition and firing means for initiating ignition of said gas generating material, isolating a zone of the well bore beneath the container with the conductor tubing extending into said isolated zone, pumping into the isolated zone through said conductor tubing fluid containing a fluiddoss-preventing material to cause the deposition of a filter cake on the Wall of the well bore in said isolated zone upon passage of such fluid into the earth formation in said isolated zone, continuing pumping until said filter cake is impermeable and a sustainable pressure below formation break-down pressure is built up in the isolated zone, temporarily halting the pumping of fluid to determine the existence of such a sustainable pressure, introducing into the conductor tubing while the pumping is halted pressure responsive means for actuating the firing means, said actuating means passing through the conductor tubing into operative contact with the firing means, and then resuming pumping to provide suflicient pressure to cause said actuating means to actuate said firing means to ignite said gas generating material and provide a surge of gas from said container to fracture the well along a line of least tensile strength of the formation in said isolated Zone.

References Qited in the file of this patent UNITED STATES PATENTS 2,645,291 Voorhees July 14, 1953 2,712,355 Hofl July 5, 1955 2,734,861 Scott et al. Feb. 14, 1956 2,766,828 Rachford Oct. 16, 1956 2,811,207 Clark Oct. 29, 1957 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noa 3,,O66fl34 December 4 1962 Robert F, Meiklejohn It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the grant lines 2 and 12 and in the heading to the printed specification line 5 name of assignee for 'B S Service Incfl' each occurrence, read B J Service, Inca column 1,, line 68 for overhurn" read overburden column 4 line 38 for "divers" read diverse 5 column 5 5 line 14, for "383 read 33 column 6, line 1 after copending" insert application line 3 after "Apparatu: insert and now Patent Nou 2,,9'ZO 647 Signed and sealed this 23rd day of July 1963o (SEAL) Attest:

ERNEST w. SWIDEE DAVID LADD Attesting Officer Commissioner of Patent

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