Halogenating Extraction Of Oil From Oil Shale

Abstract

A process for recovering oil by circulating hot fluid through a permeable mass of oil shale is improved by circulating hot fluid that contains a halogenated organic compound.

Description

BACKGROUND OF THE INVENTION

This invention relates to producing shale oil or other organic material from oil shale. It is particularly useful in producing shale oil from a subterranean oil shale.

Prior shale oil production processes have utilized a circulation of a hot fluid through a permeable mass of oil shale. It causes the kerogen or other organic components of the oil shale to be thermally converted, by pyrolysis or retorting, to fluids or solutes which are dissolved or entrained in the circulating hot fluid. In treating a subterranean oil shale, the circulating fluid is pumped through conduits in well boreholes leading to and from a permeable region within the oil shale and the produced shale oil is recovered from the outflowing fluid. The circulated fluid may be heated at a surface location or in the well borehole before it contacts the oil shale or may be heated within the oil shale by means of an in situ combustion.

The cost of operating a hot fluid circulating shale oil production process tends to be undesirably high relative to the value of the product. A significant factor in the cost of the operation is the relatively slow rate at which the oil shale can be heated by the circulating hot fluid. A primary object of the present invention is to provide a shale oil production process in which the rate of thermal fluidization and recovery of the organic components is increased by the action of a hot, reactive/extractive, fluid which tends to supplement a thermal conversion by a chemical reaction and/or dissolution that accelerates the rate of the fluidization and recovery.

SUMMARY OF THE INVENTION

In accordance with this invention, organic materials are recovered from an oil shale by circulating hot fluid containing a halogenated organic compound through a permeable portion of the oil shale and recovering organic materials from the circulated fluid. The organic materials which are produced by this invention comprise the components of a conventional shale oil supplemented and/or modified by the presence of halogenated and/or depolymerized derivatives of the relatively high molecular weight pyrolysis products of kerogen and/or bitumen. The present invention is particularly useful where a hot fluid is circulated through a permeable portion of a subterranean oil shale.

The halogenated organic compounds which are used in the present invention can be substantially any which are fluidizable and reactive with kerogen at a temperature applicable to a fluid which is circulating within a permeable portion of oil shale. The halogenated organic compound should be fluidizable in the sense of being a fluid or being soluble in a fluid at such a temperature. The fluid circulated within the oil shale can consist of substantially pure halogenated organic compound or a mixture of at least one such compound with at least one other material. Examples of halogenated organic compounds suitable for use in this invention comprise organic materials such as hydrocarbons or substituted hydrocarbons which have been halogenated with a reactive halogen such as chlorine, bromine or iodine. The chlorinated organic compounds are preferred, and the polyfunctional chlorinated organic compounds are particularly suitable. Examples of suitable compounds include the chlorides, bromides or iodides of hydrocarbons containing from about one to eight carbon atoms; the polyfunctional analogs of such compounds, such as dichlorobutane, trichloropropane, dichlorodiethyl ether, methylchloroform, a solution of a soluble salt of trichloroacetic acid, etc.

While the present invention is not premised on any particular reaction mechanism, the following may be involved in the materially enhanced rate of organic material recovery that is exhibited by the present process. At a temperature of at least a few hundred degrees Fahrenheit, the molecules of kerogen or bitumen contain, or behave as though they contain, hydrogen atoms which tend to be active. The molecules containing such active hydrogen atoms react with molecules of a halogenated organic compound to form a hydrogen halide. Such hydrogen halides are strong inorganic acids which tend to enhance the chemical conversion or solution of inorganic components of the oil shale. Such a solution or conversion of inorganic solids creates additional permeability and speeds up the heating and dissolution of the organic components. The produced hydrogen halides also tend to induce a depolymerization of long chain kerogen or bitumen molecules or their pyrolysis products and such depolymerization products tend to be more soluble or more volatile (and thus more rapidly fluidized) than the untreated portions of kerogen or bitumen or their pyrolyzates.

The present invention is particularly useful in producing shale oil from a subterranean oil shale that contains water-soluble minerals and/or heat-sensitive carbonate minerals. The presence of such minerals tends to enhance the rate of growth of a permeable zone due to the fluidization of inorganic components of the oil shale. The heat-sensitive carbonates are fluidized by both a thermal conversion to carbon dioxide and water, and a dissolution of water-soluble unreacted portions or conversion products. The hydrogen halides produced by the reaction of the halogenated organic compound used in the present invention are effective in enhancing the rate of such fluidizations of the inorganic components of the oil shale.

In situations in which it is desirable to mine portions of an oil shale formation and pyrolyze the mined oil shale in a fluid-heated, pressure-tight, surface located retort, the pyrolytic recovery of petroleum material is improved by incorporating an effective amount of halogenated organic compound in the hot fluid that is circulated through the oil shale. In such a process, chunks or fragments of the oil shale are preferably contacted with a hot aqueous and/or hydrocarbon fluid that contains at least about 2 percent by weight of at least one halogenated organic compound at a temperature of at least about 500.degree. F under a pressure sufficient to keep a significant proportion of the fluid in the liquid phase. Where the oil-shale-contacting fluid predominates in hydrocarbon components, e.g., a benzene solution of a halogenated organic compound, the oil shale is preferably preheated by contacting it with hot aqueous liquid. The contacting of chunks of oil shale with a hot aqueous liquid (i.e., with hot water utilized in preheating the oil shale and/or a hot aqueous solution containing at least one halogenated organic compound) tends to exfoliate the pieces of the oil shale. The exfoliation reduces the tendency for clinkers to be formed during the pyrolysis-extraction operation and reduces the extent to which the oil shale needs to be crushed in order to obtain an efficient recovery of petroleum material.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a vertical sectional view of an oil shale formation to which the recovery process of this invention is applied through a single well;

FIG. 2 is a vertical sectional view of the oil shale formation of FIG. 1 in which a pair of wells are used in the invention; and

FIG. 3 is a vertical sectional view of an alternate arrangement for using the invention with a single well.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring to the drawing, FIG. 1 shows a well borehole 11 extending into subterranean oil shale formation 12. Fluid communication may be established between points 13 and 14 in oil shale formation 12 and adjacent to borehole 11 along vertical fractures by, for example, a conventional hydraulic fracturing procedure. A hot fluid containing a halogenated organic compound is flowed through tubing 17 past packer 19. The fluid passes through perforations 20 and 21 in casing 22 and returns to the surface through the annular opening around tubing 17. The entrained fluidized shale oil material is recovered from the outflowing portions of the circulating fluid by procedures such as known phase separation and/or distillation procedures. Although a single well may be used, it is generally preferred to use at least a pair of wells.

As shown in FIG. 2, a pair of wellbores 23 and 24 extend into subterranean oil shale formation 25. Fluid communication is established between point 26 adjacent to wellbore 23 and point 27 adjacent to wellbore 24. In a preferred embodiment, the depths of such points may be those at which a tuffaceous streak is encountered by a pair of well boreholes between which the streak is continuous. The permeable channel extending through the oil shale may be formed by the process of locating and acidizing a tuffaceous streak as described in U. S. Pat. No. 3,481,398. At least one hot halogenated organic compound,or a fluid containing such a compound, is flowed through tubing 29 past packer 30. The fluid passes through perforation 31 in the casing 32 of wellbore 23, through points 26 and 27, and through perforation 33 in the casing 34 of wellbore 24. Fluidized materials derived from the oil shale are recovered from the circulated fluid.

In FIG. 3 the permeable zone formed within oil shale formation 12 is preferably a relatively voluminous permeable fragmented zone 35. The term "permeable fragmented zone" refers to a multiply fractured zone in which the volume of the interconnected openings within the fractures provide a void volume of from about 5 to 40 percent of the volume of the zone.

Permeable fragmented zones can be formed by known hydraulic and/or explosive techniques for fracturing subsurface earth formations. Suitable techniques are described in U. S. Pats. Nos. 1,422,204 and 3,481,398. The streak acidizing procedure of the latter patent may be used to form a channel into which a liquid explosive is injected and subsequently detonated, in order to form a generally disc-shaped permeable fragmented zone. High-power explosives, such as those produced by nuclear devices, are particularly suitable means for forming such fragmented zones. In general, the permeable fragmented zone formed by a nuclear device has a vertically extensive and generally cylindrical shape.

In circulating hot fluid through a permeable fragmented zone, the flow paths can be vertical or horizontal and can involve a radially expanding or line-drive type of displacement of the fluid within the oil shale. Generally, a substantially vertical downward flow is preferred.

In FIG. 3, zone 35 may comprise a nuclear chimney type of permeable fragmented zone. In treating such a zone, one or more wells 36 are drilled to near the bottom, preferably while the zone is hot, or at least warm, from the explosion energy. In the illustrated arrangement of FIG. 3, the well 36 is drilled and cased to near the bottom and the casing 37 is perforated at 38 and 39 and equipped for injecting fluid through the borehole annulus above packer 18, and through perforations 38 into the upper portion of the fragmented zone. Fluid is produced from near the bottom of the zone through perforations 39 and tubing string 40. The adjustment of the pressure within the permeable fragmented zone to one selected for the circulation of heated fluid is effected by controlling the rate of withdrawing fluid from the cavern relative to the rate of injecting fluid into the cavern.

As indicated in FIGS. 1 through 3, equipment and techniques, such as a conventional arrangement of a heater 41, pump 41a, separator 42, and heat exchanger 43 may be used for pressurizing, heating, injecting, producing, and separating components of the fluid that is circulated through the permeable zone 35. The production of the fluid can be aided by down-hole pumping means, not shown, or restricted to the extent necessary to maintain the selected pressure within the zone. The pressure in the zone is preferably maintained at a level suited for economically transferring heat into the zone by circulating a fluid that is economically available at the well site.

In certain situations, it is advantageous to circulate a hot fluid containing a mixture of relatively low molecular weight, predominantly aromatic hydrocarbons having relatively low critical temperatures and pressures. With such hydrocarbons (which may include significant proportions of shale oil hydrocarbons) the temperatures and pressures within the permeable zone may provide conditions approaching or exceeding the critical conditions for part or all of the circulating hydrocarbons. In the critical or super-critical region, such hydrocarbons have densities and viscosities that are intermediate between their gas and liquid states and are particularly effective in extracting organic components from oil shale.

In a preferred procedure, the hot fluid that contains the halogenated organic compound is (or contains) steam and is circulated through the permeable oil shale formation under conditions such that at least most of the steam is condensed within the oil shale. The proportion of the halogenated organic compound is preferably from about 2 to 10 percent by weight of the circulating fluid. The circulating fluid may contain the halogenated organic compound either as a solute and/or a separate fluid phase that is introduced either continuously or intermittently.

Comparative tests have been conducted with respect to the rates at which organic materials are removed from a permeable mass of oil shale through which hot fluids of various types are circulated. Such experiments have indicated that where the circulating hot fluids were, respectively, dichlorobutane, trichloropropane, dichlorodiethyl ether, and mixtures of such materials with, respectively, aromatic and aliphatic solvents for oil shale hydrocarbons, the time periods required to reduce the organic content of the oil shale to one-half of its original value (due to the circulation of the hot fluid) were significantly less than the times required where the circulating hot fluid was such a solvent free of the halogenated organic compound.

Similar improvements in the rates at which organic materials were removed were observed when the circulated fluid was a steam containing from about 2 to 10 percent by weight of at least one of the halogenated organic compounds mentioned above and the rates due to circulating steam containing a halogenated organic compound were compared with those due to steam free of those compounds.

In the tests of both of the types mentioned above, it was apparent that any halogenated organic compound in the gas phase tended to be selectively absorbed into the organic components of the oil shale to an extent tending to cause cracking or fracturing along the bedding planes of the oil shale. In addition, it was apparent that the rates and extents to which rubbling occurred within the oil shale material was enhanced by the presence of the halogenated organic compound.

Claims

What is claimed is:

1. In a process for producing shale oil by circulating steam through a permeable mass of oil shale, the improvement which comprises circulating with said steam through said oil shale mass an effective amount of at least one halogenated organic compound.

2. The process of claim 1 wherein the halogenated compound is dichlorobutane.

3. The process of claim 1 wherein the halogenated compound is trichloropropane.

4. The process of claim 1 wherein the halogenated compound is dichlorodiethyl ether.

5. The process of claim 1 wherein the halogenated organic compound is a sodium trichloroacetate aqueous solution.