Method Of Producing Oil From An Oil Shale Formation Containing Nahcolite And Dawsonite

Abstract

A new and improved method of recovering hydrocarbons and dawsonite decomposition products from a subterranean oil shale formation containing substantial amounts of nahcolite and dawsonite comprising penetrating said formation with at least one well borehole and forming a cavern therein. A hot fluid is circulated in the upper region of the cavern to effect formation of carbon dioxide by decomposition of the nahcolite and dawsonite thereby causing pressure build-up resulting in fracturization and/or rubbling and enlargement of the cavern, thereafter injecting simultaneously or sequentially into the upper region of the cavern a cooling liquid, and into the rubblized zone a kerogen-pyrolyzing fluid to recover hydrocarbons and final by recovering dawsonite decomposition products by suitable means such as solution mining.

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of copending application, Ser. No. 835,323, filed June 23, 1969 and now abandoned.

Description

BACKGROUND OF THE INVENTION

This invention relates to the recovery of hydrocarbons and dawsonite decomposition products from an underground oil shale formation containing nahcolite and dawsonite deposits by creating a cavern in said formation, decomposing the nahcolite and dawsonite to form carbon dioxide to effect pressure build-up and fracturization and/or rubbling of the oil shale, in-situ recovering hydrocarbons by means of a kerogen-pyrolyzing fluid and finally recovering the dawsonite decomposition product by solution mining or other suitable means.

Description of the Prior Art

The use of various techniques both nuclear and non-nuclear to fracture, rubblize or break-up or fragment underground oil shale formations so as to form a fractured formation or a chimney or cavern filled with rubble or fragmented oil shale to facilitate shale oil recovery from such fractured, fragmented oil shale areas by in-situ pyrolysis is well known in the art. Although some oil shale formations are known to contain nahcolite and dawsonite, their recovery in conjunction with insitu pyrolysis of shale oil recovery has not been thought feasible in the past because of the thermal decomposition of the nahcolite and dawsonite and in the case of the latter the formation of insoluble oxides and/or silica complexes of aluminum. Therefore, attempts to recover dawsonite from subterranean oil shale formations containing rich zones of nahcolite and dawsonite has not been attempted except with respect to shallow deposits from which the minerals are mined and processed at surface locations.

A number of proposals have been made in the art to recover dawsonite from oil shale above ground by subjecting an oil shale previously retorted above ground to a leaching process using an aqueous solution of sodium carbonate and sodium hydroxide and subsequently precipitating the dawsonite with carbon dioxide in order to recover dawsonite. In U.S. Pat. No. 3,502,372 in-situ recovery of oil and dawsonite from subterranean rubblized oil shale formation is described using a combination of a pyrolysis and solution mining technique involving forming a fracture-permeated zone within a subterranean oil shale formation, prior to such treatment.

The above-ground retorting techniques for recovering oil and dawsonite are outside the scope of the present invention, and are undesirable and unsuitable for carrying out the process of the present invention since the process results in the formation of large amounts of insoluble materials which are undesirable and difficult to handle making these operations costly and unattractive. The process described in U.S. Pat. No. 3,502,372 is more attractive and less costly than an above-ground retorting technique but tends to cause a formation of some insoluble products and a failure to recover a significant proportion of the dawsonite.

OBJECTS OF THE INVENTION

It is an object of this invention to provide an improved method for recovering hydrocarbons and dawsonite decomposition products from underground oil-shale formations containing nahcolite-dawsonite deposits.

Still another object of this invention is to decompose the nahcolite and dawsonite of an underground oil-shale formation rich in these minerals to carbon dioxide to aid in the fracturing and rubbling of the formation; insitu recovering hydrocarbons therefrom by means of a kerogen-pyrolyzing fluid and finally recovering the insoluble complexes of aluminum from the decomposed dawsonite.

Still another object of this invention is to circulate a hot fluid preferably along the roof of the cavern to effect formation of carbon dioxide by decomposing the nahcolite and dawsonite to cause enlargement of the cavern and fracturization and/or rubbling of the oil-shale therein, cooling the roof or upper portion of the cavern to terminate this process; injecting a kerogen-pyrolyzing fluid into the rubbled oil shale to effect recovery of hydrocarbons therefrom and finally recovering the dawsonite decomposition products containing water insoluble aluminum complexes.

Still another object of this invention is that the cavern in the oil shale formation containing the nahcolite-dawsonite zones is formed by leaching a portion of the nahcolite and thereafter forming carbon dioxide by decomposing the remaining nahcolite and dawsonite by means of a hot fluid such as steam.

Still another object of this invention is that the kerogen-pyrolyzing fluid to effect hydrocarbon recovery from the oil shale and the cooling fluid used to prevent vertical migration of the cavern roof can be circulated through the cavern sequentially or simultaneously.

SUMMARY OF THE INVENTION

These and other objects are preferably accomplished by forming a cavern preferably one which is generally horizontally controlled in a subterranean oil shale-bearing formation that is impermeable and contains a significant proportion of nahcolite and dawsonite below its upper boundary region and providing fluid communication between the earth surface and the cavern. Hot fluid is injected and circulated through the cavern in its upper region and should preferably be in contact with the roof thereof at a temperature sufficient to cause decomposition of the nahcolite and dawsonite and form carbon dioxide and water thereby causing a high pressure build-up within portions of the cavern and cause fracturing and rubbling of the roof of the cavern. As the volume of the hot fluid within the cavern increases, the paths of fluid flow within the cavern are preferably adjusted to keep the hot fluid in contact with the upward migrating roof of the cavern. The fluid circulation is continued for a time sufficient to enlarge the cavern by a significant amount. The cavern roof is cooled prior to its migration above a selected depth, such as an upper boundary region of the normally impermeable hydrocarbon-bearing formation, by displacing a cooling fluid into contact therewith. Relatively cool fluid is maintained in contact with the roof of the enlarged cavern while circulating a kerogen-pyrolyzing fluid through the hydrocarbon-bearing material within the cavern to recover hydrocarbons therefrom and finally solution mining to recover the dawsonite decomposition products.

The process of this invention is particularly applicable to various subsurface oil shale formations, such as in the Green River formation in the Colorado area of the United States, containing rich deposits of nahcolite and dawsonite. The nahcolite and dawsonite are apt to occur within an oil shale formation in the form of beds, lenses, nodules, loads, veins, or the like, having sizes ranging from microscopic particles to layers that are many feet in thickness and many miles in extent. Dawsonite is particularly apt to occur in the form of microscopic particles in amounts of up to about 10 or 12 percent by weight of the oil shale while the nacholite can vary in amounts of 5-40percent.

The present process provides a means for enlarging a permeable zone within a normally impermeable oil shale by circulating a hot fluid such as hot water, steam, mixtures thereof or non-aqueous fluids to effect decomposition of the nahcolite and dawsonite present therein to carbon dioxide at a temperature between about 300.degree. F and about 1,500.degree. F, preferably between 350.degree. F and 750.degree. F. The invention also provides a means for terminating the enlargement of the permeable zone at a selected depth and avoiding the danger of extending fractures to surface or subsurface locations that would create a danger or disadvantage by means of cooling fluids. It further provides a procedure that generates significant amounts of carbon dioxide as a circulating fluid which also has a significant stripping action on the hydrocarbon materials released from the heated oil shale by a kerogen pyrolyzing fluid which may be an aqueous or non-aqueous pyrolyzing fluid or by use of hydrocarbon extracting materials such as phenols etc. Oil shale begins to release hydrocarbons at significant rates at temperatures from about 400.degree. F and preferably between 550.degree. and 750.degree. F. In the presence of carbon dioxide, the hydrocarbons released from the oil shale by a pyrolyzing fluid such as steam tend to be entrained and transported in the form of vapors. This provides both an economy in the recovery of hydrocarbon products and their upgrading. The utilization of the carbon dioxide and water that are generated in-situ can be used as a part of the hot fluid that is circulated along the cavern roof to cause vertical expansion of the cavern within a subterranean oil shale and results in a significant increase in the amount of shale oil recovered.

The recovery of dawsonite decomposition products can be finally recovered by solution mining using an aqueous fluid preferably containing a chelating agent.

The chelating agents useful as additives in the aqueous alkaline fluid of this invention can include any organic chelating agent capable of chelating with the aluminum or other prevalent metallic compounds present in the oil shale and forming soluble compounds in the aqueous solution and include nitrogen-containing carboxylic acids and amine or metallic salts thereof such as amino-, imino-, nitrilo-, carboxylic acids and salts thereof such as described in U.S. Pats. Nos. 2,631,978; 2,959,547; 3,256,196 and 3,409,551 and include amino carboxylic acids, e.g., ethylene diamine tetraacetic acid and salts thereof methyl iminodiacetric acid, nitroacetic acid, phenyl iminodiacetic acid, 1, 2-diamino cyclohexane tetraacetic acid of which preferred are the amine and alkali metal (sodium) salts of ethylene diamine tetraacetic acid, e.g., di-, tri- and tetrasodium ethylene diamine eteraacetate (Na.sub.2 -, Na.sub.3, or Na.sub.4 EDTA), 1, 2-diamino cyclohexane tetraacetic acid and mixtures thereof.

The presence of the chelating agent in the aqueous alkaline solutions aids in the recovery of dawsonite decomposition products which are substantially insoluble aluminum compounds, such as analcite.

SPECIFIC EMBODIMENT OF THE INVENTION

The procedural steps in carrying out the process of the present invention are essentially as follows:

1. establishing at least one well borehole into a nahcolite-dawsonite rich oil-shale formation;

2. forming a cavern therein by leaching a portion of the nahcolite with an aqueous fluid such as water which may be cool or hot, preferably the latter;

3. circulating a hot fluid such as hot water and/or steam in the upper region and preferably along the cavern roof to effect decomposition of the nahcolite and dawsonite to carbon dioxide and water insoluble products of dawsonite such as insoluble oxides and silicates complexes of aluminum such as analcite to effect enlargement of the cavern by upward migration of the cavern roof as well as fracturization and/or rubbling;

4. circulating sequentially or simultaneously a cooling fluid such as hydrogen along the cavern roof and a kerogen pyrolyzing fluid such as steam and/or solvents such as benzene phenol, etc. through the rubbled oil shale to effect hydrocarbon recovery; and

5. solution mining to recovery the aluminum complexes from dawsonite.

EXAMPLE

Into an oil-shale formation rich in nahcolite and dawsonite a well was completed at below about 2000 feet and a portion of the nahcolite bed was water leached to form a cavern. Steam was injected along the cavern roof to decomposition the nahcolite and dawsonite to form carbon dioxide thereby building up pressure and cause upward migration of the cavern roof and oil shale rubbling. The dawsonite is essentially converted to water insoluble complexes of aluminum such as analcite. A cooling fluid hydrogen is thereafter circulated along the cavern roof to prevent further upward roof migration while steam is injected into the oil shale rubble to effect hydrocarbon recovery thereafter.

After the hydrocarbons such as oil have been recovered a basic solution containing a chelating agent such as an alkali metal salt of ethylene diamine tetraacetic acid, e.g., Na.sub.4 EDTA (the sodium salt of ethylenediaminetetraacetic acid) or Na salt of 1, 2-diamino cyclohexane tetraacetic acid is injected into the treated oil recovery zone of the shale formation preferably at a temperature of from about 100.degree. F to about 500.degree. F to effect recovery of analcite.

The foregoing description of the invention is merely intended to be explanatory thereof. Various changes in the details of the described method may be made within the scope of the appended claims without departing from the spirit of the invention.

Claims

I claim as my invention

1. A method of producing hydrocarbons and dawsonite decomposition products from a subterranean oil shale formation containing rich deposits of nahcolite and dawsonite comprising the steps of:

a. penetrating at least one well borehole into an underground nahcolite-dawsonite oil shale formation;

b. injecting a nahcolite leaching solution to create a cavern;

c. circulating a hot fluid along the cavern roof to release carbon dioxide from the nahcolite and dawsonite and thereby increasing the volume of the cavern by effecting rubbling;

d. injecting a cool fluid along the enlarged cavern roof while injecting a kerogen-pyrolyzing fluid into the oil shale rubble and recovery hydrocarbons therefore; and

e. recovering water insoluble dawsonite decomposition products.

2. The method of claim 1 wherein the leaching solution in step (b) is hot water and the hot fluid in step (c) is steam.

3. The method of claim 1 wherein the decomposed dawsonite is recovered by solution mining.

4. The method of claim 3 wherein the decomposed dawsonite is essentially analcite.

5. A method of producing hydrocarbons and analcite from an underground oil shale formation rich in nahcolite and dawsonite comprising the steps of:

a. penetrating at least one well borehole into an underground oil shale formation rich in nahcolite and dawsonite;

b. leaching a portion of the nahcolite with hot water to create a cavern;

c. circulating steam along the roof of cavern to release carbon dioxide from the nahcolite and dawsonite the latter being converted to analcite to enlarge the cavern vertically and rubble the oil shale;

d. injecting a cooling fluid along the roof of the cavern;

e. injecting steam into the rubbled oil shale and recovering hydrocarbons therefrom; and

f. recovering analcite by solution mining.