US3106244A - Process for producing oil shale in situ by electrocarbonization - Google Patents

Description

Oct. 8, 1963 H. w. PARKER 3,106,244

`PROCESS FOR PRODUCING OIL SHALE IN SITU BY ELECTROCARBONIZATION Filed June 20, 1960 2 Sheets-Sheet 1 28 lNJBrloN PRODUCTION D-Q30 AIR PRODUCTION INJECTION INJACIION 28 PRODUCTION 243 .Z( LDq-@BO INVENTOR. H.W. PARKER BY g A T7' ORNE YS O.- 8, 1963 H. w. PARKER 3,106,244

PROCESS FOR PRODUCING OIL SHALE IN SITU BY ELECTROCARBONIZATION Filed June 20, 1960 2 Sheets-Sheet 2 32 AIR OR 2e STEAM SHALE oll.

4 AND GASES OXIDIZING PRODUCTION GAS F/G.5 I4 INVENTOR. 15 H. w. PARKER A TTORNE Ys United States Patent O 3,105,244 PRCESS FR PRDDUCNG @IL Si-IALE IN SlTU BY ELECTROCARBONIZATIN Harry W. Parker, Bartlesville, Gkla., assigner to Phillips Petroleum Company, a corporation of Delaware Filed June 20, 1960, Ser. No. 37,451 11 Claims. (Cl. 16S-11) This invention relates to Van improved process for producing oil shale in situ.

The production of oil from oil shale without removing the shale from the deposit is rendered difficult by the impermeable `character of the shale. This is particularly true with reference to recovery of the oil by in lsitu combustion or other heating processes. One method of producing oil shale in situ is disclosed in my copending application S.N. l27,627, hled May 9, 1960, wherein electrocarbonization of the shale is utilized as a means of distilling hydrocarbons from the shale bed. This invention is concerned with an extension and modiication of the electrocarbonization process disclosed in said application.

Accordingly, it is an object of the invention to provide an improved process for producing oil from oil shale in situ. Another object is to provide an improved process for producing shale by electrocarbonization and in situ combustion. A yfurther object is to provide a method of extending the zone in which electrocarbonization is effected when utilizing this method for the in situ production of oil shale. Other objects of the invention will become apparent to one skilled in the art upon consideration of the accompanying disclosure.

In accordance with one aspect of the invention, a substantial section of a shale bed is electrocarbonized around a production well therein so as to distill hydrocarbons therefrom and produce hot permeable coke therein at combustion supporting temperature; thereafter a free-oxygen-containingV gas is injected into an offset injection well from which fractures lead to the carbonized section so that the injected gas passes into the hot section thereby igniting the hot carbon; the combustion is continued by continuing the injection `of said gas; and the lluids produced by lthe electrocarbonizing step and the combustion step are recovered thru the production well. In this process the shale surrounding the electrocarbonized section radially outwardly therefrom is radially fractured by the expansion of said section during the electrocarbonizing step.

The method of effecting the electrocarbonizaltion step is disclosed in the above-identified copending application and comprises, broadly, positioning a pair of electrodes in a well in contact with the shale and insulated from each other except thru the shale, and passing current thru the shale Ibetween the electrodes by establishing sufficiently high voltage potential across the electrodes. Broadly, this method is well defined in the prior art as applied to carbonaceous deposits containing a conducting medium, such as salt water.

One embodiment of the invention comprises injecting the (D2-containing gas thru the injection well at suicient concentration and rate to move the combustion front established in the permeable coke at the outer periphery of the coked section to the wall of the production Well. This burns out the coke from the permeable area and renders the burned out area electrically non-conductive so that reestablishment of a high potential difference across the electrodes forces a current to flow thm the shale more remote from the production well and thru the shale surrounding the previously coked section. This has the effect of expanding the produced and coked zone farther into the sha-le from the produc- 3,1%,244 Patented Get. 1963 tion well. In order to facilitate current flow across the fractures, particulate conductive media, such as copper, iron, alumina, etc., may be injected with a suitable fluid.

Another embodiment of the invention comprises injecting Oz-containing gas thru either the injection well or the production well so as to ignite the coke in the electrocarbonized section and move a combustion zione or front thru the coke into the shale adjacent the fractures leading to the injection well, thereby producing hydrocarbons from the shale `adjacent the fractures. After the shale is burned in this manner and the unproduced shale deeper in the stratum from the fractures is heated to elevated temperatures, further electrocarbonization is readily effected by placing one of the electrodes in the injection well in contact with the shale and flowing current thru the hot shale from one well to the other. This me-thod produces additional oil from the shale and can be followed by another burning step. This additional burning step is effected by injecting OZ-containing gas into the shale fromeither one of the we-lls and producing from the other.

A further embodiment of the invention comprises injecting particulate Isolid conductive material such as particles o-f metal, graphite, iron, zinc, magnesium, aluminum, etc., into the fractures between the wells after the electrocarbonizat-ion step, and placing one of the electrodes in the injection Well. The establishment o-f high potential between the electrodes now has the effect o-f passing current thru the fractures from conductive particle to conductive particle, thereby heating the adjacent shale so as to render the same conductive. Continued passage of current electrocarbonizes the shale adjacent the fractures and distills hydrocarbon material therefrom. This step is then followed by a combustion step effected by injecting O2-containing gas thru either one of the wells and producing thru the other. After the coke is burned out in this manner, further electrocarbonizing is effected in the hot shale adjacent the denuded area.

Another material which can be utilized in the process to make it possible to pass current thru the fractures comprises a slurry of carbon particles in brine. "It is helpful to incorporate in the brine a dissolved organic compound which is carbonizable, such as sugar or molasses. Graphite powder wet with oil is also a successful conducting material for electrocarbonizing in the fractures.

-In shale beds in which the fracturing due to swelling 0f the electrocarbonized section around the production well is of such small magnitude as to render operation difcult, it is feasible to artificially fracture the intervening shale between the injection wel-l, or a plurality of wells in a ring around the production well, and the production well so that the fractures formed by the electrocarbonization are expanded and/or new fractures are formed extending from the injection wells into the eleotrocarbonized section.

A more complete understanding of the invention may be had by reference to the accompanying schematic drawing of which yFIGURE l is a vertical section thm an oil shale bed showing an arrangement of apparatus for effecting one embodiment of the invention; FIG- UREZ is a similar view showing another arrangement of apparatus; FIGURE 3 is a similar view showing a further arrangement of apparatus `for effecting another embodiment of the invention; lFIGURE 4 is a similar View showing aonther embodiment of the invention; and FIGURE 5 is a plan view of a well pattern useful in effecting the invention.

Referring to FIGURE l, a subterranean shale bed lll is penetrated by wells 12 and 14 closely spaced therein (about to 5G feet). he wells are provided with casings 1o and 1S extending substantially to the upper level of the shale. Casing is provided with well head 2G thru which tubing 22 extends. An air injection conduit 214 passes thru the upper end of the casing. Casing 1S is provided with weil head 26 thru which tubing 28 extends and the conduit 31B passes thru the upper end of the casing. Conduits 23 and 31? provide air injection and product takeoff means. Casing 15 is connected by lead line 32 to generator 33 or other power source to serve as one electrode, and electrode 34, positioned in well 12 in contact with a shale or with conductive material forming a path to 'the shale, is connected by lead 36 with generator 33.

In operation with the arrangement shown in FIG- URE l, the shale adjacent Well 12 is heated by any suitable means so that it becomes conductive and a high potential is established between casing 16 and electrode 34 so as to heat the intervening shale and distill hydrocarbons therefrom. In instances in which the shale ccntains suiicient electrolyte (salt water), or is otherwise conductive, the preliminary heating step may be omitted. In most instances shales are substantially dry and nonconductive and the heating step is essential before the shale `intermediate the electrodes can be eiectrocarbonized. In dry `oil shale, the method of my above-identi .fied application may be utilized to provide the essential heat step. This method comprises packing well 12 between electrode 34 and the lower end of casing 16 with a conductive material in particulate form and placing at an intermediate level therein a high resistance section which melts after the heating step has continued sufficiently to heat the wall of the well, thereby cutting oif ow thru the conductive material and requiringr the current to flow thru the shale at the periphery of the well. The conductive material may comprise iron filings or steel wool on which copper sulfate solution has been flushed, or [steel wool wet with graphite brine paste. In this type of operation it is essential to insulate lead 36 from the conductive packing material.

After the heating step has been effected, the electrocarbonization of the shale around well 12 is commenced and continued until a substantial section 42 bounded by lines 38 has been carbonized and rendered permeable. During the electrocarbonizaticn step, fractures 40 are extended radially outwardly from the carbonized section 42. This is caused by the swelling of section 42 during the electrocarbonizing step. Fractures 40 include both vertical and horizontal fractures. Well 14 is within the pattern of fractures 40 surrounding well `12 Aand this opens up the formation to well 14 so that injection of air thru either well 12 or well 14 forces air thru the shale via the fractures to the opposite well. By injecting air thru well 14 at -a suflicient rate, a combustion `front or zone is established in section 42 in the hot coke therein and the front is moved by inverse drive to well 14 with production being recovered thru `well 12.

By injecting air or other Ogicontaining gas such as diiuted air, oxygen-enriched air, or pure oxygen, thru well .12 into the hot coke in section 42, a direct drive combustion front is established `and moved thru the shale via the fractures to well 14 from which the produced fluids are recovered in conventional manner thru tubing 28 or line 30.

Referring to FIGURE 2, the arrangement shown therein is similar to that of FIGURE l, but in addition to the electrodes in well 12, an additional electrode 50 is positioned in well 14 and connected by lead 53 with the same lead from generator 33 as connects with lend 36. Switches 54 and 56 are provided for changing the voltage application from electrode 34 to electrode 5t). The arrangement shown in FIGURE 2 is intended to be utilized after the electrocarbonization step and the in situ combustion step described in rel-ation to FIGURE l have taken place. The in situ combustion step burns hydrocarbon in the 4 shale and distills additional hydrocarbon along the fractures so as to heat the unprcduced shale between the fractures sufliciently high to render electrocarbonization effective when high potential is applied to electrodes 16 and 5t). In this manner additional oil is distilled from the shale to increase the production therefrom.

Referring now to FIGURE 3, electrode 58 comprises a tubing string extending substantially to the bottom of the shale bed. The lower section of the well is packed around tubing 5S with a conductive material 66 so that by application of high voltage to electrodes 16 and 553 the surrounding shale is electrocarbonized to 'for-rn a porous hot coked section of shale 42. In order to drive the produced yand coked section 42 farther into the shale, a fracture system is established from Well 14 to section 42 as by placing packers 62 and 64 in well 14 and exerting fluid fracturing pressure thru tubing 28. Fracturing system 66 is thus formed extending from well 14 to Iwell 12, .preferably after the electrocanbonizing step or during the final phase thereof. While the coke in section 42 is at cornbustion supporting temperature, air is injected thru tubing 28 and thru fracture system 66 into the hot coke at a relatively slow rate so that a direct drive combustion zone is moved from the outer periphery of the hot coke to the wall of well 12, thereby producing a clean, :burnedout section of shale 63 within section 42. A direct drive combustion zone always burns the formation clean so that it is no longer a conducting medium for an electric current. Now, by again establishing a lhigh potential between electrcdes 16 and 53 the current is forced to flow therebetween around coked section 42 because of the non-conducting section 68. In this manner electrocarbonization of an additional outer section 70 of the shale bed is produced and coked. This operation can be repeated `by again propagating a direct drive combustion front from the outer boundary of the coked section 70 along the fracture to the previously denuded section 68.

Another embodiment of the invention effective with the arrangement shown in FIGURE 2, comprises injecting solid particulate yconductive material, such as metal tilings, into the fracture system 40 extending from well 14 to woll 12 so that a conductive passageway is provided along the fractures to burned and carbonized section 42. By applying high potential 'across electrodes 34 and Si) the shale adjacent the fractures is heated to distill hydrocarbons therefrom, leaving a hot cc-ked residue in the shale which is permeable and amenable to in situ combustion to further heat the intervening shale. Here again, alternate combustion and electrocarbonization is effected in producing ,the remaining carbonaceous material in the shale between wells 12 and 14.

The direction of moving the combustion front when injecting O2containing gas thru well 14 with the arrangement shown in FIGURE 3 is determined by the rate at which the gas is injected and/ or by the composition (O2 content) of the gas. High ilow rates, usually 20 standard cubic lfeet per hour per square feet cross sectional area of the front, produce inverse or countercurrent drive of the front. At lower rates of air injection, the resulting drive is direct (concurrent). The direct drive of the front is also effected by reducing the O2 concentration in the injected gas as by diluting air with combustion gas. Increasing the O2 concentration in the injected gas above the normal 2O volume percent favors inverse movement of the front. A combination of these .two factors, viz., injecting rate and O2 concentration, can be utilized to control the direction of the fron-t movement. A convenient method of moving the front from the outer periphery of the coked section 42 to well 12 is to inject an admixture of air and steam such as an admixture containing from 10 to 50 volume percent steam. Steam in adrniXture with air burns the hot coke yand effects the water gas reaction.

FiGURE 4 shows the stratum 1G carbonized around each of wells 12 and 14 in the area within the boundaries alessia carbonization has been effected `as shown, the stratum may be produced further by igni-ting the shaile around either well and feeding combustionsupporting gas, such as air,

to the combustion zone to move the combustion front thru the stratum to the other well. This drive may be effected by either inverse or direct injection of air. The combustion front goes thru the `fractures in the impermeable uncarbonized section so vas to produce hydrocarbons from the shale adjacent the fractures.

In ya. further embodiment of the invention, fractures 40 in FIGURE 4 may be rendered conductive by introducing thereto particulate conductive material. Suchl conductive materialincluding powdered metals is disclosed in the prior art such asin the patent to Dixon2,818,ll8 issued December 31, 1957. After the conductive Inlaterial -is disposed in .the fractures, current is passed between electrodes in wells 12 and 14, as shown in FIGURE 2, so xas to heat the shale adjacent the fractures whereby the hot shale becomes conductive and oil is produced from the shale. The passage lof current thru the fractures is continued so as to electrocanbonize shale deeper into the formation above and below the fractures and thereby expand the carbonized zone. Fluids produced during preceding steps are recovered thru either Well or in the manner illustrated in FIGURE 5` where well 14 represents a welll in a ring of wells and well 12 is a central well. Of course, a combustion front can be passed thru the carbonized shaile following the preceding sequence of steps.

In any of lthe figures of the drawing, Well 14 may represent a wvell in a ring of wells surrounding welll 12. FIG- URE 5 illustrates such `a well pattern wherein gas, such as air, for supporting combustion is injected thru line 211 into a distributing ring 15 Yfor injection into wells 14 thru feed lines -17 extending from ring 15 to each weil. The production is recovered from well 12 thru line 19 and passed to product separation means not shown. It is also Ifeasible to inject ythe combustion-supporting gas thru line -19 and recover production thru wells 14 by means of lines 17, ring 15 and line 21.

lCertain 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 Ion the invention.`

'I claim: Y

1. A process for producing oil shale in situ which comprises heating -a section of said shale around a production well therein to render said section electrically conductive;

while the section is hot, electrocarbonizing said section so as to distill hydrocarbons therefrom and lproduce hot permeable coke therein at a combustion supporting ternperature; continuing the electrocarbonizing step until shale `in said section is fractured radially outwardly from the carbonized section; thereafter injecting a free-oXygen-containing gas into an offset injectionwell from which at least one fracture leads to said section so that `said gas passes into said section and ignites said hot carbon; continuing the combustion; land recovering fluids produced by the electrocarbonizing step and the combustion step thru said production well.

2. The process of claim 1 wherein said shale is fractured radially outwardly to said injection well from the carbonized section by expansion of said section during the electrocarbonizing step.V

3. The process of claim 2 wherein a ring of injection wells surround said production well within the fractured area and said gas is injected thru said ring of wells.

4. The process of claim 1 wherein at least one of the flow rate of said gas `and the concentration of O2 therein is regulated so as to move la combustion front thru said fractures toward said injection well.

5. A process compris-ing heating a dry, nonconducting oil shale to a sufficiently high temperature to render same electrically conductive; electrocarbonizing a section of the vheated shale around a first Well therein; continuing the electrocarbonizing step until said shale is fractured radially outwardly from the carbonized section by expansion of said section; electrocar-bonizing a second section of said shale around an offset well therein; continuing the electrocarbonizing step until the shale surrounding the second carbonized section is also fractured to rform a ow path with aforesaid fractures between the wells; thereafter ignitng and moving a combustion front thru said shaleV between said wells; and recovering fluids produced 'by the electrocarbonization and combustion steps.

6i. The process of claim 5 wherein said combustion front is initiated around one of said Wells by injecting air into same and moving said front by direct drive to the opposite well.

7. The process of claim 5 wherein the hot carbon in the carbonized section `around one Well is cooled below combustion supporting temperature and air is injected thru said one well so that it passes to the hot carbon in the carbonized section around the opposite well, thereby igniting saine Iand moving said combustion front by inverse drive to said one well.

8. A process -for producing an `oil shale in situ which comprises electrocarbonizing a substantial section of said shale `around a first well therein so as to distiill hydrocarbons therefrom and produce hot permeable coke therein atcombustion supporting temperature; continuing the electrocarbonizing step until fractures extending radially outwardly from said section are produced by expansion of said section; providing -a second well in said shale within the fractured yarea; injecting free-oxygen-containing gas into the hot coke so as to ignite same and establish in situ combustion; `continuing the injection of said gas so as to move a combustion zone thru said shale to said second well; and recovering fluids produced by the carbonization and combustion steps.

9. The process `of claim 8 wherein air is injected thru said first well so `as to move said combustion front by direct drive.

10. The process of claim 8 wherein air is injected thru said second well so las to move said combustion `front by inverse drive.

ll. A process comprising electrocarbonizing a section of shale around la iirst well; continuing the electrocarbonizing step until said shale is fractured radially outwardly from the carbonized section by expansion of said section during the'electrocarbonizing step; electrocarbonizing aV second section of said shale around an offset well therein; continuing the ellectrocarbonizing step until the shale surrounding the secondwc'arbonized section is also fractured to form a flow path with aforesaid fractures between the wells; thereafter depositing particulate conductive material in said fractures; and passing current between an electrode in said first well 'and an electrode in said second well thru and along said fractures solas to heat the adjacent shale whereby the hot shale becomes conductive; continuing the passage of current to electrocarbonize the shale adjacent the fractures |and to expand the carbonized Zone; and recovering produced fluids from one of said wells.

References Cited in the file of this patent UNITED STATES PATENTS 2,795,279 Sarapu June ll, 1957 2,818,118 Dixon Dec. 3l, 1957 2,967,052 Crawford Jan. 3, 1961k OTHER REFERENCES Mining Congress Journal October 1949, page 57.

Claims (1)

1. A PROCESS FOR PRODUCING OIL SHALE IN SITU WHICH COMPRISES HEATING A SECTION OF SAID SHALE AROUND A PRODUCTION WELL THERIEN TO RENDER SAID SECTION ELECTRICALLY CONDUCTIVE; WHILE THE SECTION IS HOT, ELECTROCARBONIZING SAID SECTION SO AS TO DISTILL HYDROCARBONS THEREFROM AND PRODUCE HOT PERMEABLE COKE THEREIN AT A COMBUSTION SUPPORTING TEMPERATURE; CONTAINUING THE ELECTROCARBONIZING STEP UNTIL SHALE IN SAID SECTION IS FRACTURED RADIALLY OUTWARDLY FROM THE CARBONIZED SECTION; THEREAFTER INJECTING A FREE-OXYGEN-CONTAINING GAS INTO AN OFFSET INJDECTION WELL FROM WHICH AT LEAST ONE FRACTURE LEADS TO SAID SECTION SO THAT SAID GAS PASSES INTO SAID SECTION AND IGNITES SAID HOT CARBON; CONTINUING THE COMBUSTION; AND RECOVERING FLUIDS PRODUCED BY THE ELECTROCARBONIZING STEP AND THE COMBUSTION STEP THRU SAID PRODUCTION WELL.

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