US 3004594 A
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d 3 REFERENC Oct. 17, 1961 F. w. CRAWFORD PROCESS FOR PRODUCING OIL Filed Nov. 19, 1956 INVENTOR F.W. CRAWFORD BY g z A 7' TORNEYS 3,004,594 Patented Oct. 17, 1961 3,004,594 PROCESS FOR PRODUCING OIL Francis W. Crawford, Bartlesville, 01th., assignor to Phillips Petroleum Company, a corporation of Delaare Filed Nov. 19, 1956, Ser. No. 622,992
Claims. (Cl. 166-l1) This invention relates to an improved method of in situ combustion in recoveryof hydrocarbons from underground formations oflow permeability containing hydrocarbon material.
The recovery of hydrocarbons from hydrocarbon-containing underground formations by in situ combustion has come into considerable prominence in recent years, particularly in the recovery of'oil from shale and other formations of low permeability. One of the difliculties involved in in situ combustion techniques is the difficulty in transporting oxygen (air) to the combustion zone. This is particularly true in impervious or only slightly permeable formations. The present invention provides an improved method of providing air passageways in a formation of low permeability and simultnaeously establishing and/or promoting combustion with movement of the combustion zone thru the formation.
Accordingly, it is an object of the invention to provide an improved process for recovery of hydrocarbons from a hydrocarbon-containing formation by in situ combustion. Another object is to provide an improved techni-- que for establishing air passageways from one or more input Wells to a production well in the initial stages of in situ combustion utilizing inverse flow of air. A further object is to provide an improved method of fracturing a formation and simultaneously propping the fracture open without the aid of special propping agents. Other objects of the invention will become apparent from a consideration of the accompanying disclosure.
In order to practice in situ combustion in a hydrocarbon-containing formation, such as an oil shale,'it is of prime importance to have means for transporting oxygen to the combustion-zone and means for the removal of liquids and gases. If natural fractures for the transportation of air or oxygen exist in the shale forma tion, the countercurrent or inverse air method can be used without further fracturing. If there are no fractures, or if the fractures are inadequate, the formation can be fractured by any of the recognized ways to pro-.
.Vide air channels. Ordinarily, oil'shale formations are impevious to air and therefore no channels are usually found. Hence, it is essential to in situ combustion in a formation of low permeability to airto provide fractures for the passage of air and other gases thru the formation.
A more recent technique employed in in situ combustion is appropriately designated as inverse air injection. In this type of operation, combustion is initiated around a production borehole and air is injected into the formation thru one or more surrounding boreholes at suificient pressure to cause the 'air to flow thru the formation or fractures therein to the combustion zone so as to support combustion therein and advance the combustion front countercurrently to the flow of air. This technique is disclosed and claimed in the co-pending applicaair in surges.
with a compressible fluid such as air, alone, or in admixture with a liquid as in the aerated drilling fluid technque, almost no special equipment is required. The fracturing fluid is readily available and the dynamic response of the formation to the fluid is advantageous. In field tests of the invention-utilizing air as the fracturing fluid, the air pressure during injection exceeds a critical value of about one p.s.i.g. per foot of depth (for a well approximately 50 feet in depth) at which time the injection well takes Surging is evidenced by surging of the pressure gauge on the well headand by surging of the automatic compressor. When the injection pressure is reduced by one or two p.s.i.g. the surging stops. This livery of fluid by the compressor. This is in contrast to the use of an incompressible fluid, such as oil, where slight flow into new fractured'areas reduces the pressure below that required for further fracturing and the pumps must supply a large volume of additional fluid rapidly in order to effect adequate fracturing. Another advantage of the present technique lies in the low cost of the fracturing fluid and the simplicity of the equipment .re-
' quired. The instant method also eliminates the requiretion of I. C. Trantham et al., Serial No. 529,916, filed ment of propping agents. After a fracture is made, alternately decreasing and increasing the pressure of the fracturing gas creates debris in the fracture which functions as a propping agent. The fracturing gas rushes out of and into the fracture by this procedure, as the pres sure is rapidly varied to produce a fluttering action. A specific advantage is obtained when air or other combustion supporting gas is utilized as the fracturing fluid because the fracturing of the formation renders the combustion supporting gas immediately available at the ignition well for the start of in situ combustion or for advancing the combustion zone radially outwardly from the ignition well or borehole in the event a combustion zone has already been established around the injection well.
A more complete understanding of the invention may be had from-a consideration of the accompanying drawing which is a schematic elevation of apparatus in a formation for effecting the process of the invention.
Referring to the drawing, a formation 10 underlying an overburden 12 is penetrated by an ignition borehole 14 and an injection borehole 16. These boreholes are provided wtih casings 18 and 20, respectively. Casing 20 is cemented in,- at least thru the formation as at 22. Casing 18 terminates at about the upper level of the formation. The well head or casing 18 is provided with a gas outlet line 24 and tubing 26 for use in recovering liquid products by conventional methods. Casing 20 is closed and is provided with fluid injection line 28 which leads from afluid surge tank "30 to a suitable level in the well such as the level between packers 32 and 34. A line 29 connects with casing 20 and with an air source (not' shown). Pressure or surge tank 30 has connected with its lower section a line 36 in'which is positioned a compressor 38 for supplying pressurized fracturing fluid and/or injection air to borehole 16.
The casing and cement at various levels in formation 10 in borehole 16 is penetrated in known manner by perforations 40 which serve as openings into the formathe formation to initiate or sustain combustion in the formation around the production well and advance the combustion front toward the input wells. Fracturing tion for fracturing and for injection of combustion supportingfluid. Formation 10 is fractured at several levels 42-and these fractures extend from injection well 16 to ignition well '14 to provide continuous passageways for combustion supporting gas. Areas, 43 are initial combustion zones.
In practicing the invention with the arrangement of apparatus shown in the drawing, a set of fractures-in horizontal planes at different levels is produced. The
' selective fracturing is effected by perforating the casing and cement at the selected levels and then packing off the casing by means of packers 32 and 34 so that fracturing 'fluid enters the packed off area thru the line 28 extending thereto without being supplied to the other selected areas. After fracturing of the formation at one selected level the packers are moved to the next selected level and the procedure is repeated until all of the horizontal fractures desired are produced. It is also feasible to fracture at more than one level at the same-time. It 1 in situ combustion by inverse air injection is immediately established and can be continued merely by injcctfon of air thru borehole 16. After ignition andin situ combustion are initiated in this manner at the topmost level illustrated in the drawing air is injected thru line 29 while packers 32 and are repositioned for the next fracturing step. Succeeding fracturing steps are effooter! in the same manner with initiation of the in situ combustion inverse air injection technique operating automatically in each fracture and at each fracture level as fracturing air reaches borehole 14. I
Burning of hydrocarbon in the fractures heats the formation above and below the fractures so as to render the hydrocarbon therein more fluid and fiuidi'zes solid hydrocarbon (kerogen) present in the formation. In this manner a substantial proportion of the hydrocarbon matcrial in place in the formation is retorted therefrom and is recovered in both gaseous and liquid form from well bore 14 by conventional means, gases being recovered from line 24 and liquids thru tubing 26.
Continued injection of air thru borehole 16 gradually moves the combustion front thru the formation to the injection well and continued injection of air after the combustion front arrives at well 16 effects the reversal of the combustion front and drives the same back to ignition well 14. This phenomenon which is known as thermal echo is supported by combustion of residual coke deposited in the formation on the initial burnthru by combust'on of hydrocarbons condensedin the formation back of the combustion area during inverse air injection and other hydrocarbon materialdrivcn from the formation during the inverse air injection phase.
While the drawing and discussion relate to an operation utilizing one injection well 16, in the practical application of the process in the field, a 5 or 7-spot well pattern is generally utilized in effecting recovery of the hydrocarbon material from a generally circular area around a production or ignition well 14. The invention has been described principally in its application to impervious oil shale but it is not restricted to this application. Other hydrocarbon-containing formations of low permeability to air such as coal deposits and, particularly, lignitic deposits which are of low porosity, are amenable to production by inverse air in situ combustion in the manner of the invention.
While the discussion of fracturing relates chiefly to air as the compressible fracturing fluid, air or other gas may be mixed with a liquid such as hydrocarbon oil or water in proportions which render the. mixture '(aerated liquid) sufficiently compressible to function to advantage in fracturingin accordance with the invention. The function of the gas in the mixture is to build up a potential of readily available pressure which acts quickly and automatically to increase the fracturing once a fracture is initiated. When hydrocarbon oil is utilized in the fracturing fluid, it provides additional readily combustible fuel for heating the formation and retorting the hydrocarbon therefrom. The term "mixture" as used herein includes alternate slugs of liquid and gas as well as a froth of gas and liquid.
Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.
1. A process for recovering hydrocarbons from a formation of low permeability containing hydrocarbons comprising penetrating said formation with first and second spaced-apart boreholes within fracturing distance thru said formation; producing a fracture in said formation from the first to the second of said boreholes by direct application of fracturing pressure thereon thru the first'borehole from a sufficiently large volume of readily compressible fluid comprising gas to provide surges of fluid into said fracture to immediately occupy and extend same deeper into the formation and maintain supporting pressure to hold said fracture open, thereby establishing gas communication thru said fracture between said boreholes; alternately decreasing the fluid pressure in said first borehole so as to close said fracture and then increasing said pressure so as to open said fracture, thereby causing rapid flow of gas out of and into said fracture to create and shift debris therein which acts to prop said fracture'open when said fluid pressure is reduced below a supporting level, heating an area of said formation adjacent said second borehole to a combustiornsupporting temperature of said hydrocarbon therein; while said area is at said temperature flowing pressurized combustion-supporting gas thru said fracture to the heated area so as to initiate and support combustion of the hydrocarbon material in said area; continuing the flow of said combustion-supporting gas to said area so as to cause the resulting combustion front to move thru said formation countercurrently to the flow of said gas; and recovering hydrocarbon fluid produced by said -combustion from said second borehole.
2. The process of claim 1 utilizing air as the compressible fracturing fluid and as the combustion supporting gas.
3. The process of .claim 1 wherein said compressible fluid comprises a mixture of hydrocarbon oil and a gas.
-4. The process of claim 1 wherein said compressible fluid comprises a mixture ofa hydrocarbon oil and air.
5. The process of claim 1 wherein said compressible fluid comprises a mixture of water and air.
6. A process for fracturing a carbonaceous formation which comprises penetrating said formation with first and second boreholes within fracturing distance thru said formation; producing a fracture in said formation from the first to the second of said boreholes by direct application of fracturing pressure thereon thru one of said boreholes from a sufliciently large volume of readily compressible fluid comprising gas to provide surges of fluid into said fracture to immediately occupy and extend same deeper into the formation from said one borehole and maintain supporting pressure to hold said fracture open; after fracturing has occurred, alternately decreasing the fluid pressure so as to close the fracture and increasing said fluid pressure so as to open the fracture and cause said fluid to rush out of and into said fracture thereby creating debris therein which serves as a propping agent. 7. The process of claim 6 wherein said fluid is air. 8. The process of claim 7 including the steps of heating said formation adjacent the other of said boreholes to at least combustion temperature before said fracture is made so that same is ignited as air reaches the hot area thru the fracture; continuing the feeding of air thru said fracture to the ignited area to propagate a combustion front thru said formation; and recovering produced hydrocarbons thru said second borehole.
9. A process for fracturing a carbonaceous formation which comprises penetrating said formation with first and second boreholes within fracturing distance thru said formation; producing a fracture in said formation from the first to the second of said boreholes by direct application of fracturing pressure thereon thru said first borehole from a suificiently large volume of combustion supporting gas to provide surges of fluid into said fracture to imediately occupy and extend same deeper into the formation and maintain supporting pressure to hold said fracture open; before said fracture is made, heating said formation adjacent said second borehole to at least combustion temperature so that same is ignited as said gas reaches the hot area thru said fracture; continuing the feeding of said gas thru said fracture to the resulting combustion front to cause same to move thru said formation toward said first borehole; and recovering produced hydrocarbons thru said second borehole.
10. The process of claim 9 using air as the pressurizing and as the combustion-supporting gas.
References Cited in the file of this patent UNITED STATES PATENTS 2,584,605 Merriam et al. Feb. 5, 1952 2,712,355 Hoff July 5, 1955 2,734,579 Elkins Feb. 14, 1956 2,734,861 Scott Feb. 14, 1956 2,754,911 Spearow July 17, 1956 2,766,828 Rachford Oct. 16, 1956 2,777,679 Ljungstrom Ian. 15, 1957 2,780,449 Fisher et a1. Feb. 5, 1957 2,793,696 Morse May 28, 1957 2,901,043 Campion et a1. Aug. 25, 1959