US3428125A - Hydro-electropyrolysis of oil shale in situ - Google Patents

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1 mu; r pw g xR 394289125 1969 I H. w. PARKER 3,428,125

HYDRO-ELECTROPYROLYSIS OF OIL SHALE IN SITU Filed July 25, 1966 CASING IN SHALE FRACTU RES 6 O O (TCYTG CASING BRINE IN FRACTURES lNVEA/TOR H.W. PARKER BRINE H2O A r TOR/V5 vs 7 United States Patent o 3,428,125 HYDRO-ELECTROPYROLYSIS OF OIL SHALE' IN SITU Harry W. Parker, Bartlesville, Okla., assignor to, Phillips' Petroleum Company, a corporation of Delaware Eiled July 25, 19 66, SenNo. 567,530 U.S. Cl. 163-248 7 Claims Int. Cl. E215 43/24, 43/26 ABSTRACT OF THE DISCLOSURE Hydrocarbons are recovered from an oil shale formation insitu by injecting an electrolyte into the formation.

through two?- or more wells and imposing a potential drop across the formation between the'wells to pass gelectrical current therethrough and heat the same, to a temperature sufiiciently {high to pyrolize the hydrocarbons therein, while maintaining sufiicient pressure on theforgnationto prevent vapibrization of the electrolyte. The wells. may be linked together through the formation byiracturing or directional drilling, or a combination of both.

In another. aspect, the invention relates to varying thepressure required to prevent vaporization of the electrolyte in inverserelation to the ratio of the weight of salt to the weight of water when an aqueous salt is used asthe electrolyte.

In another aspect, the invention relates tothe production of hydrocarbons and non-condensable gases from oil shale by injecting an aqueous electrolyte intothe formation through two or more wells, and impressing a voltage betweentwo of said wells to heat the formation, while maintaining sufficient pressure on said formation to prevent vap r'i'zation of said electrolyte, and' producing gas and/or!) :through one or more other wells. Alternatively, the prod can also be removed from the formation via the wells'iirjnpressed with the voltage.

In U.Sf Patent 3,137,347, pyrolysis of oil shale in situ by means of electrocarbonization was disclosed. The cost of electrical power was recognized to be a major item in the operation ofthe process, but no solution was advanced. It is an object of this invention to reduce the power needed to pyrolyze oil shale in situ. Another object of the invention is to produce hydrocarbons and noncondensable gases from oil shale at lower temperatures than were heretofore possible.

Other aspects, objects and the several advantages of the invention will be apparent to one skilled in the art upon studying the drawing, specification, and appended claimssodium sulfate, sodium carbonate, and so on. It will be apparent to one skilled in the art that the addition of various electrolytes to water is a variable which can be controlled. A high electrolyte content in the water would raise the boiling point of the Water and thus reduce the pressure necessary to pyrolyze the shale.

The technique of hydro-electropyrolysis canbe applied after electrocarbonization: has been started in the manner described in U.S. Patent 3,137,347 or hydro-electropyrolysis can be used from the beginning. In one specific embodiment, two wells aredrilled at a distance from one another in the oil shale formation, an electrolyte such as an aqueous salt is injecte'ti' therethrough, an electrical potential is impressed across the casings of saidlwells to heat the shale formation; andsufficient pressure: is maintained on the formationfto prevent vaporization of the electrolyte. The wells may be linked together by either fracturing or directional drilling, or by a combination of thetwo. By-the latter method, directional drilling need not be relied upon todirctly hit another well. Regardless of the method used to link the wells, the electrolyte is injected into the formation under sufficient pressure to fracture the shale between the wells, and the pfessure is maintainedso as to prevent vaporization of the electrolyte.

After the heating zone has been established in "the shale, it can be extended indefinitely by drilling additional wells into the shale, injecting electrolyte into the formation under sufficient pressure to fracture same, and applying electrical current to heat thefshale while maintaining a pressure sufficient to preventgvaporization of the electrolyte. Said additional wells canj be directionally drilled so that a greater spacing would result.

The hydrocarbons and fnon-condensable gases produced by the process of this invention can be recoveredZ-by drillingone or more producing wells between the Wells impressed with electrical current. These wells mus also be pressured to prevent vaptjrization of. the: electrolyte.

Referring now to the drawings: e

A multi-well system is iillustrated' in combination with means for practicing one embodiment of the invention.

Well bores 1 and 2 hold casings 3 and 4 through which a suitable electrolyte suchgas brine is delivered to formation 11 by means of purn 8. Pressure sufficient to fracture the formation is su. lied by pumps 8. A source of electrical current 6 is used to heat the formation, while pressure means 7 maintain sufficient pressure on the formation to prevent vaporization of the electrolyte. Oil and non-condensable gases can be recovered from formation 11 via production well 5 which is cased.

Anelectrical connection is made between the easing of the two wells 3 and 4 filth the electnical circuit being completed through the brine in the fractures connecting the two wells in the oil shale zone. The casing is cemented to the well bore face near the oil shale zone in a conventionalmanner. A high voltage AC. or DC. potential of 440 volts or higher applies potential between the two wells to heat the formation with sufiicient back pressure of up to 1530 p.s.i.g. maintained on the wells so that temperatures of between 500 F. and 600 F. are maintained in the brine in the fractures 9 and 10. In this manner, the formation between the two wells is heated and the shale pyrolyzed at moderate temperatures below 750 F. Heating in this manner is continued for several months prior to production of the produced oil through cased production well 5;. Production well 5 is produced by flowing or by. a pump not shown. Oil and gas can be produced during the heating period.

Brine which may be saturated can be injected into casings 3 and 4 during the heating process. It is preferred that a saturated solution of brine be used as this will allow better conduction of current and thus more heating of the formation. The following concentrations of brine in water for different salts can be used depending upon the temperature of the water.

Percent Sodium chloride 39 Calcium chloride 60 Potassiumchloride 50 Sodium sulfate 40 Sodium carbonate 40 The amount of salt which can bedissolved in the water is a function of the temperature of the solution, and the water can be heated prior to injection in order to as nearly as possible saturate the water withfthe particular salt being used. The invention is not limited; to the use of any particular salt, but sodium chloride 'is preferred since it is readily available in ground waters.

It will be apparent to one skilled in the art that it is possible to make fuel gas from the coke remaining on the shale after it has been retortedQhy injecting air and/or steam into the spent shale. Removal of coke by air and/or steam will also prevent current flow through the spent shale.

In the practice of the invention, low temperatures are maintained by introducing increments of electrolyte into the formation while maintaining s ufficient pressure to keep the temperature at the desiredfll evel. For example, to pyrolyze at 600 F., it is necessary to maintain a pressure of 1530 p.s.i.g. If the shale locally becomes hotter than 600 F., the water will boil and the steam will transfer heat to cooler portions of the formation.

In principle, the concept of the invention is to raise the temperature of the shale sufiiciently high to pyrolyze the hydrocarbons therein, while maintaining sufficient pressure on the formation to prevent vaporization of the electrolyte.

Reasonable modification and variation are possible within the spirit and scope of the invention, theessence of which is producing hydrocarbons and non-condensable gases from oil shale in situ by injecting an electrolyte into the shale and applying electrical current thereto while maintaining pressure sufficient to prevent vaporization of the electrolyte.

I claim:

1. A method for producing hydrocarbons from oil shale formations in situ penetrated by at least two wells which comprises fracturing said formation to increase the overall flow permeability between said wells through said foramtion, introducing an aqueous electrolyte into said foirnation to increase the electrical conductivity of said formation, imposing a potential drop across said formation to promote current flow therethrough and consequent heating thereof and maintaining jsuf ficient pressure on, said formation to retain an aqueous electrolyte coductiive phase'within said formation.

2. A "'method in accordance with claim 1 wherein said electrolyte is a mixture of water and an inorganic salt.

3. A" method according to claim 2 wherein said inorganic salt is an alkali metal salt.

4. A'method according to claim 1 wherein said electrolyte is injected into said oil shale using gas pressure to fracture said oil shale and to maintain pressure sufficient to, prevent vaporization of said electrolyte.

5. The method of claim 1 wherein the amount of said aqueous electrolyte injected is suflicient to produce a substantially continuous conductive path through said formationibetween said wells.

.6. The method of claim 1 wherein the said potential drop is suflicient to substantially elevate the temperature of said formation and increase the mobility of said hydrocarbons 7. The method of claim 6 wherein said temperature is elevated by an amount of up to about 600 F.

References Cited UNITED STATES PATENTS STEPHEN J. NOVOSAD, Primary Examiner.

' US. Cl. X.R.

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