US3915234A - In situ production of hydrocarbon values from oil shale using H{HD 2{B S and CO{HD 2{B - Google Patents

Abstract

Kerogen is recovered from oil shale deposits by introducing CO2 and H2S in water into the deposits under pressure and then shutting in the deposits to allow the H2S and CO2 solutions to dissolve the inorganic matrix material in the deposits. Kerogen is then recovered from the deposits, preferably as a colloidal suspension.

Description

l6-3O7 l 0 2 SE 399159.234 United States Patent 11 1 1111 3,

Pelofsky Oct. 28, 1975 [54] IN SITU PRODUCTION OF HYDROCARBON. 3,322,194 5/1967 Strubhar 166/307 V LUE FROM 01 SHALE USING 5 AND 3,484,364 12/1969 Hemminger 208/1 1 CO 3,565,784 2/1971 Schlinger et a1. 208/1] 2 3,605,889 9/1971 Closmann et al, 166/307 [75] Inventor: Arnold H. Pelofsky, East Brunswick, 3,617,472 1 H1971 Schlinger et a1 208/11 N 3,700,280 10/1972 Papadopoulos et al. 166/271 0 3,739,851 6/1973 Beard 166/254 Asslgneel Clues Service Research & 3,741,306 6/1973 Papadopoulos et a1 166/271 Development Company, Cranbury, 3,753,594 8/1973 Beard 166/271 NJ. 3,804,169 4/1974 Closmann 166/272 3,804,172 4/1974 Closmann et a]. 166/272 [22] Filed: Aug. 28, 1974 [21] Appl. No.: 501,310 Primary Examiner-Henry C. Sutherland Assistant Examiner-Jack E. Ebel Attorney, Agent, or Firm-George L. Rushton [52] US. Cl 166/307; 299/5 [51] Int. Cl. E21B 43/16; E21B 43/25 [58] Field of Search 166/271, 305 R, 307; [57] ABSTRACT 208/11; 252/855 (3; 299/5 Kerogen is recovered from oil shale deposits by introducing CO and H 8 in water into the deposits under [56] References C'ted pressure and then shutting in the deposits to allow the UNITED STATES PATENTS H S and CO solutions to dissolve the inorganic matrix 3,074,877 1 /l963 Friedman 208/11 material in the deposits Kerogen is then recovered 3,122,493 2/1964 Thomsen 208/11 from the deposits, preferably as a colloidal suspension. 3,265,608 8/1966 Crawford 1 208/11 3,278,233 10/1966 Hurd et a1 299/4 7 Claims, 2 Drawing Figures US. Patent Oct. 28, 1975 3,915,234

22 FIG.

IN SITU PRODUCTION OF HYDROCARBON VALUES FROM OIL SHALE USING H S AND CO BACKGROUND OF THE INVENTION This invention relates to the recovery of hydrocarbon substance, largely insoluble in benzene, and which is dispersed throughout an inorganic matrix composed principally of carbonates along with other minor constituents. The kerogen in oil shale is relatively rich in hydrogen and will yield a benzene-soluble material (bitumen) on heating.

Many proposals have been made for recovering usable hydrocarbons from oil shales, most of which involve the use of heat in one form or another to soften or liquefy the kerogen for conversion to bitumen or for further conversion to produce both liquid and gaseous products. The heat may be applied in situ, or the shale may be mined by conventional mining methods, with subsequent heating or retorting of the mined shale. In conventional in situ retorting, a heating agent is injected into one or more wells extending into the shale deposit, and product is produced through the same or separate wells. It is also known to inject air into the formation to ignite the kerogen and form a combustion front which is then moved through the formation in a conventional manner to liquefy and partially gasify the kerogen and carry the liquid and gaseous products through the formation to wells from which it may be recovered. In situ processes frequently involve fracturing the shale deposit to facilitate contact between heating agents and kerogen.

It has also been suggested that kerogen can be recovered from shale deposits by dissolving the inorganic matrix, either by the use of solvents such as water or acidified water or by introduction of microorganisms. Such processes have not, however, proven satisfactory and generally must rely on fracturing or otherwise breaking up the deposits to allow contact with the solvent or microorganisms over a sufficiently large area.

It is an object of the present invention to recover kerogen from shale deposits by means of a novel in situ recovery process.

SUMMARY OF THE INVENTION Hydrocarbon values are recovered from a subterranean deposit of oil shale by introducing a mixture of H 5 and CO in water under pressure into the deposit. This is preferably accomplished by introducing water, CO and H 8 into the deposit through wells extending into the deposit. Introduction of water, CO and H 5 is continued until the pressure in the deposit at the point of introduction is increased to between about 200 and about 1000 psi above the formation pressure of the deposit. The deposit is then shut in until the pressure drops to less than about 50 psi above formation pressure, at which time hydrocarbon values, usually in the form of kerogen, may be recovered'from the deposit. In a preferred embodiment, the sequence of injection of H 8, CO and water under pressure, followed by shutting in until pressure drops, is continued until the acids have penetrated the deposit throughout spheres of a radius between about 50 and about 500 feet about the points of introduction. It is also preferred in practicing the invention that the CO and H 5 dissolved in water be introduced into the deposit as a saturated aqueous solution, between about 30 and about volume percent of which comprises a saturated solution of CO with the remainder being a saturated aqueous solution of H 5.

BRIEF DESCRIPTION OF DRAWING FIG. 1 is vertical, cross-sectional view illustrating use of the present invention in recovery of hydrocarbon values from an oil shale deposit.

FIG. 2 is a horizontal, cross-sectional view further illustrating use of the invention in recovering hydrocarbon values from oil shale deposits.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an improved method for recovering hydrocarbon values from shale deposits by at least partially dissolving the inorganic matrix of the deposits, thereby substantially increasing the permeability of the deposit. The kerogen in the deposits may then be recovered by suitable means such as in the form of a colloidal suspension or may be further converted in situ as by the use of heat, microorganisms, etc. in a conventional matter for recovery of hydrocarbon values in the form of bitumen. It is the purpose of the present invention to increase permeability of the shale deposits to the point where conventional methods such as those mentioned above for recovery of hydrocarbon values from the deposit may be employed.

In the chemical art, it is well recognized that CO dissolved in water forms a weak acid written as H CO Similarly, H 5 can be dissolved in water. And it is further recognized that both of these solutions are dilute, in that the amount of gas dissolved in a unit of water is somewhat low, e.g., about 28.2 g. of CO dissolve in 1 liter of water at 100 C and atm. Thus, although saturated solutions of CO and H 5 in water are described, it is customary to physically entrap additional gas, by pressure, in the solvent water, thereby having a reserve of gas available to ensure saturation of the solution. The combination of gases dissolved in water can be simply expressed as H 8 and CO in water."

While any convenient method may be used for contacting H 5 and CO with the inorganic matrix of the shale deposit, it is preferred that an aqueous medium saturated with H 8 and CO be used. The H 8 and CO may be added to the water at the surface or more preferably at or near the bottom of the wells extending into the shale deposit. Saturated aqueous solutions of CO and H 8 are preferred. Greater solubility is obtained using water not contaminated with inorganic material but for practical reasons of availability and cost, brine such as connate water obtained from the shale deposit or surrounding formations is frequently a preferred medium. Use of such solutions increases the time required for dissolving inorganic matrix material because of the lower solubility of the gases in the brine as opposed to fresh water. While the desired acids can, of course, be formed by adding CO and H 8 either at the surface or at the bottom of the wells, it will generally be found to be cheaper and therefore more desirable to pump the gas and water separately and add the gas to the water at the bottom of the injection wells.

For convenience, the term H SH O" will be used in this disclosure to represent the phrase, H S dissolved in water.

The inorganic matrix of typical shale deposits comprises about 95 percent quartz, feldspars, dolomite and calcite with the remaining 5 percent including illite clay materials, pyrite and analcite. The particular combination of acids used in practicing this invention, i.e., H SH O and H CO formed by saturating water with H 8 and CO is especially beneficial because certain of the components of the inorganic matrix are readily dissolved by the H CO while some other components are usually dissolved by the H SH O. This combination of acids also gives better results than other possible solvents, such as sulfuric or nitric acid, and leads to fewer environmental problems in the event of seepage out of the deposit into the surrounding water sheds or formations. While an especially preferred mixture of acids for use in practicing this invention comprises about 50 percent by volume of water saturated with H 8 and 50 percent by volume of water saturated with CO ranges between about and about 70 percent for either the H S- or the CO -saturated water are completely acceptable. An excess of gas is normally used in saturating the water to insure maximum concentration of acid. The water itself can, as mentioned above, be fresh water or brine. Connate water, recycled water, etc., may, of course, be used. Gases may be added to the water in the wells by aspiration or other suitable techniques and the degree of saturation can readily be checked by measuring the pH of the resulting solution. An increase of 2 pH units from the maximum acidity obtainable generally indicates the need for addition of increased quantities of gas.

In practicing the invention, H S-H O and H CO formed as described above by introduction of H S and CO into water being injected into the deposit through wells, may be forced into the deposit under pressure until the pressure at the bottom of the wells is raised to between about 200 and about 1000 psi above the formation pressure of the deposit. The wells are then shut in to allow time for the acid mixture to dissolve the inorganic matrix. As dissolution occurs, the acid spreads through the deposit and pressure gradually drops. When pressure has dropped to less than 50 psi above formation pressure of the deposit, hydrocarbon values may be recovered from the deposit, although it is preferred that the steps of injecting water saturated with CO and H 8 and then shutting in the wells to allow pressure to again drop to near formation pressure be continued until the H2sH2O and H CO have penetrated the formation (by dissolving the inorganic matrix) throughout spheres of a radius of between about 50 and 500 feet from the bottom of each injection well. To avoid loss of kerogen to surrounding formations, it is preferred that the peripheries of these spheres remain at least 50 feet from the boundaries of the shale deposit.

Once the permeability of the formation has been sufficiently increased by dissolving inorganic matrix as described above, kerogen may be recovered directly from the deposit or may be converted into bitumen for recovery of hydrocarbon values from the deposit in a conventional manner. A preferred method of recovering hydrocarbon values involves the recovery of kerogen in the form of a colloidal suspension in water and for this purpose suitable surfactants such as benzene sulfonic acid, naphthenic acid or isostearic acid may be added in suitable amounts such as 0.1 to 1 volume percent to facilitate formation of free flowing suspensions. Such suspensions may frequently contain between about 10 and about 30 weight percent kerogen. Alternatively, other means of recovering hydrocarbon values, such as heating the kerogen or adding microorganisms to the injected water to transform kerogen to bitumen, may be employed. It should be understood that in producing either colloidal suspensions of kerogen or in producing bitumen from the shale deposit following treatment in accordance with the invention, primary, secondary and even tertiary production techniques may be used.

In practicing the invention, it will generally be found that, following raising of the pressure at the bottom of the wells to between about 200 and 1000 psi above formation pressure, a period of at least about 2 weeks will be required for the pressure to drop to within about 50 psi of formation pressure and that a total time of between 1 month and about 1 year is frequently required to obtain the desired penetration of the shale deposit throughout the spherical volumes referred to above. While kerogen or hydrocarbon values in other forms may be recovered at the end of each of the above described pressure cycles, it is preferred that such withdrawal not be attempted until the degree of penetration described above has been obtained since efficiency is thereby increased.

In practicing the invention, it is important to avoid fracturing the shale deposit since fractures formed be yond the area of deposit from which it is desired to withdraw hydrocarbon values may result in excessive loss of bitumen into other areas of the deposit in instances where kerogen is transformed to bitumen and in any event fractures extending to the boundaries of the deposit will result in excessive loss of kerogen or bitumen to permeable surrounding or underlying forma tions or overburden. For this reason, it is preferred that the invention be practiced in shale deposits having a thickness of at least about 200 feet and that the periphery of each of the spheres of effected area in which the inorganic matrix is dissolved by the H CO and H SH O remain a minimum of at least about 50 feet from the boundary of the deposit. Overlapping of such affected spheres is of course permissible and frequently desirable to insure maximum recovery of hydrocarbon values, but it is preferred that overlapping be kept to the minimum necessary to obtain desired recovery of hydrocarbon values.

While this invention may be operated at elevated temperatures if desired, such operation usually leads to excessive loss of heat and it is therefore preferred that the invention be practiced at ambient formation temperature. Furthermore, the solubility of H 8 and CO decreases with increasing temperature.

Referring to the drawings, FIG. 1 shows a well 12 extending from the surface of the earth 114 through overburden formation 16 into a shale oil deposit 18. An underlying formation 20 is also indicated. The well 12 may be suitably lined and equipped with tubing, etc in a conventional manner. A conduit 22 communicates at one end thereof to the top of the well 12. The other end of conduit 22 may be connected to a source of injection fluid such as water saturated with H 8 and CO or may be connected to means for recovering kerogen or bitumen from the shale deposit 18. Means (not shown) are also provided for closing off the conduit 22 completely to shut in the well 12.

As an example of recovery of hydrocarbon values from oil shale in accordance with a preferred embodiment of the invention, water having a brine content less than 50 ppm is introduced through the conduit 22 into the well 12. Half of this water is saturated with CO and half with H 8, thereby forming a mixture of H CO and H SH O. This acid mixture is pumped down well 12 to deposit 18 under 1000 pounds pressure until the pressure at the bottom of the well reaches 600 psi (200 psi above formation pressure). The well 12 is then shut in for a period of 1 month during which time the acid solution dissolves the inorganic matrix in the deposit 18 and the pressure at the bottom of the well gradually drops to 450 psi (50 psi above formation pressure), at which time the acid solution has penetrated the deposit to the extent indicated by the sphere 24 in FIG. 1. The well is then opened up again and injection of acid solution under pressure resumes until the pressure again rises to 500 psi at the bottom of the well. The well is again shut in until pressure drops to 50 psi, at which time the acid solution has penetrated the deposit to an extent indicated by a sphere 26. Following a third cycle of pressure injection, a total volume of the deposit enclosed within a sphere 28 has been effected by the acid solution and has been made sufficiently permeable for kerogen to be recovered through the well 12 in the form of a colloidal suspension. To facilitate this withdrawal of kerogen, 1 percent of a commercial surfactant material (benzene sulfonic acid) is included within the acid solution injected through the well 12 during the injection cycles described above. Total elapsed time to dissolve the inorganic matrix and render the deposit permeable within the sphere 28 is about 6 months.

To recover maximum hydrocarbon values from a shale formation, it is generally desirable to use more than one well similar to the well 12 of FIG. 1. This is illustrated in FIG. 2, which shows an oil shale deposit 32 with a number of wells such as 34 and 38 completed within the shale deposit. By injection of H CO and H SI-I O as described above, with periodic shutting in of wells, hydrocarbon values may be recovered from wide areas of the deposit. The spheres of affected areas of the deposit in which this occurs are indicated generally in FIG. 2 by dashed circles such as 36 and 40. It will be noted that these spheres overlap so as to recover hydrocarbon values from the maximum possible volume of the deposit and that none of the spheres reaches the boundary of the deposit. By keeping the spheres from reaching the boundary of the deposit and avoiding fracturing of the shale, it is possible to take advantage of the extremely low permeability of the natural shale deposit to prevent any loss of hydrocarbon values before they can be produced from the deposit.

While the invention has been described above with respect to certain preferred embodiments thereof, it willbe understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.

I claim:

1. A process for recovering hydrocarbon values from a subterranean deposit of oil shale which comprises the steps of a. introducing H 8 and CO in water under pressure into said deposit until the pressure in the deposit at the point of introduction of H 5 and CO in water is between about 200 and about 1000 psi above the formation pressure of the deposit;

b. then shutting in the deposit until the pressure at the point of introduction drops to less than about 50 psi above the formation pressure of the deposit; and

c. then recovering hydrocarbon values from the deposit.

2. The process of claim 1 in which the H 8 and CO in water mixture is formed by injecting water into the shale deposit through wells and introducing H 5 and CO into such water at an elevation within the shale deposit.

3. The process of claim 1 in which steps a and b are repeated until the reactant mixture of H 8 and CO in water has penetrated the shale deposit throughout spheres having a radius of between about 5 0 and about 500 feet from the points of injection of such acids-into the deposit, each of said spheres being at least about 50 feet from the boundary of the deposit.

4. The process of claim 2 in which the H SH O and H CO are formed, respectively, by saturating water with H 5 and CO 'and in which the resulting solution comprises between about 30 and about volume percent water saturated with CO with the. remainder comprising water saturated with H 8. v

5. The process of claim 1 in which H 8 and CO in water are introduced into the deposit by saturating water with CO and H 8 and then injecting said water into wells extending into the deposit.

6. The process of claim 1 in which hydrocarbon values are recovered from the shale deposit in the form of kerogen in colloidal suspension in water.

7. The process of claim 6 in which surfactant is added to the H SH O and H CO to facilitate suspension of kerogen therein for withdrawal of kerogen from the deposit.

Claims (7)

1. A PROCESS FOR RECOVERING HYDROCARBON VALUES FROM A SUBTERRANEAN DEPOSIT OF OIL SHALE WHICH COMPRISES THE STEPS OF A. INTRIDUCING H2S AND CO2 IN WATER UNDER PRESSURE INTO SAID DEPOSIT UNTIL THE PRESSURE IN THE DEPOSIT AT THE POINT OF INTRODUCTION OF H2S AND CO2 IN WATER IS BETWEEN ABOUT 200 AND ABOUT 1000 PSI ABOVE THE FORMATION PRESSURE OF THE DEPOSIT, B. THEN SHUTTING IN THE DEPOSIT UNTIL THE PRESSURE AT TH POINT OF INTRODUCTION DROPS TO LESS THAN ABOUT 50 PSI ABOVE THE FORMATION PRESSURE OF THE DEPOSIT, AND C. THEN RECOVERING HYDROCARBON VALUES FROM THE DEPOSIT.

2. The Process of claim 1 in which the H2S and CO2 in water mixture is formed by injecting water into the shale deposit through wells and introducing H2S and CO2 into such water at an elevation within the shale deposit.

3. The process of claim 1 in which steps a and b are repeated until the reactant mixture of H2S and CO2 in water has penetrated the shale deposit throughout spheres having a radius of between about 50 and about 500 feet from the points of injection of such acids into the deposit, each of said spheres being at least about 50 feet from the boundary of the deposit.

4. The process of claim 2 in which the H2S-H2O and H2CO3 are formed, respectively, by saturating water with H2S and CO2 and in which the resulting solution comprises between about 30 and about 70 volume percent water saturated with CO2, with the remainder comprising water saturated with H2S.

5. The process of claim 1 in which H2S and CO2 in water are introduced into the deposit by saturating water with CO2 and H2S and then injecting said water into wells extending into the deposit.

6. The process of claim 1 in which hydrocarbon values are recovered from the shale deposit in the form of kerogen in colloidal suspension in water.

7. The process of claim 6 in which surfactant is added to the H2S-H2O and H2CO3 to facilitate suspension of kerogen therein for withdrawal of kerogen from the deposit.

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