U.S. patent number 3,739,851 [Application Number 05/201,941] was granted by the patent office on 1973-06-19 for method of producing oil from an oil shale formation.
Invention is credited to Thomas Noble Beard.
United States Patent |
3,739,851 |
Beard |
June 19, 1973 |
METHOD OF PRODUCING OIL FROM AN OIL SHALE FORMATION
Abstract
A method of producing hydrocarbons and optionally water-soluble
minerals from a subterranean or underground oil shale formation
containing zone(s) of water-soluble minerals by forming
interconnecting cavities or a cavern within said water-soluble
mineral-containing oil shale formation by fluid leaching the
water-soluble minerals and simultaneously or sequentially flowing a
hot fluid into the upper portion of the cavern in order to place
the cavern roof including the cavern wall under stress so as to
effect oil shale spalling and rubbling and improve recovery of
hydrocarbons.
Inventors: |
Beard; Thomas Noble (Denver,
CO) |
Family
ID: |
22747917 |
Appl.
No.: |
05/201,941 |
Filed: |
November 24, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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860349 |
Sep 23, 1969 |
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770964 |
Oct 28, 1968 |
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75009 |
Sep 24, 1970 |
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Current U.S.
Class: |
166/254.1;
166/261; 166/272.6; 166/259; 166/271; 299/4 |
Current CPC
Class: |
E21B
43/281 (20130101); E21B 43/2405 (20130101) |
Current International
Class: |
E21B
43/28 (20060101); E21B 43/16 (20060101); E21B
43/24 (20060101); E21B 43/00 (20060101); E21b
043/24 (); E21b 043/26 (); E21b 043/28 () |
Field of
Search: |
;166/272,271,303,308,248,254,258,259,269 ;299/4,5 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"How to Complete Thermal Wells" Oil & Gas Journal, Apr. 17,
1967, pp. 179 & 180 relied on..
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Primary Examiner: Novosad; Stephen J.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of copending patent
application Ser. No. 860,349, filed Sept. 23, 1969, now abandoned,
which in turn is a continuation-in-part of patent application Ser.
No. 770,964, filed Oct. 28, 1968, which has been abandoned and
replaced with copending continuation-in-part patent application
Ser. No. 75,009, filed Sept. 24, 1970.
Claims
We claim as our invention:
1. A method of recovering hydrocarbons from a subterranean oil
shale formation rich in water-soluble minerals comprising creating
a cavern in the mineral zone of the formation by solution
dissolving the water-soluble mineral, placing the roof of the
cavern under stress, by circulating a hot fluid along the roof of
the cavern so as to effect spalling and rubbling of oil shale
cavern roof into the cavern while effecting pyrolysis with a hot
pyrolysis fluid of the rubbled oil shale and recovering
hydrocarbons therefrom.
2. The method of claim 1 wherein the water-soluble mineral
dissolving solution is an aqueous fluid and the hot fluid
circulating along the cavern roof effecting spalling and rubbling
of the oil shale and the hot pyrolysis fluid is steam.
3. The method of claim 2 wherein the aqueous fluid is hot
water.
4. The method of claim 3 wherein the water-soluble mineral is
nahcolite.
5. The method of claim 2 wherein the aqueous fluid is steam.
6. The method of claim 5 wherein the water-soluble mineral is
nahcolite.
7. The method of claim 1 wherein the water-soluble mineral are
water-soluble carbonates.
8. The method of claim 7 wherein the carbonate is nahcolite.
9. In a method for producing oil from a subterranean oil shale
formation containing an adjacent underlying zone of rich
water-soluble minerals comprising the steps of:
a. determining the location of said zone that is rich in
water-soluble minerals within said oil shale formation;
b. extending at least one well borehole into the water-soluble
mineral containing zone and establishing communication between the
well borehole and the water-soluble mineral containing zone;
c. dissolving the water-soluble minerals by circulating therein via
the borehole and into the mineral-containing zone an aqueous
dissolving liquid and creating a fluid-filled cavern having a
predominantly areally extensive void space therein sufficient to
place the roof of the cavern in tension;
d. circulating a hot fluid through the cavern along flow paths
controlled to keep the hot fluid in contact with the roof of the
cavern causing oil shale in contact and adjacent to the cavern roof
to rubble and cave into the cavern;
e. flowing an in-situ oil recovering fluid into said rubblized oil
shale cavern (d); and
f. recovering shale oil therefrom.
10. The method of claim 9 wherein communication step (b) is
effected by fracturing.
11. The method of claim 9 including the step of recovering mineral
by-products from the aqueous liquid circulating out of the other of
said borehole locations.
12. The method of claim 9 including the steps of:
providing at least said one well borehole with casing extending
along said zone and into said earth formations at least a short
distance below said zone; and
providing said casing with slip joint means for varying the length
thereof.
13. The method of claim 9 including the step of circulating hot
aqueous fluid into contact with the roof of said cavern while
flowing said kerogen-pyrolyzing fluid through said cavern.
14. The method of claim 9 wherein the step of circulating aqueous
liquid through said zone to leave a cavern therein includes the
step of circulating aqueous liquid through said zone until a cavern
is formed therein extending at least 50 feet or more along at least
one horizontal direction while extending over an area at least
several hundred square feet and having a volume of at least several
hundred cubic feet.
15. In a method for producing oil from a subterranean oil shale
formation containing an adjacent underlying zone of rich
water-soluble minerals comprising the steps of:
a. determining the location of the rich-water-soluble mineral zone
within the oil shale formation,
b. extending at least a pair of well boreholes within the zone rich
in water-soluble minerals;
c. establishing fluid communication between at least one pair of
said wells by injecting an aqueous liquid via each of said
boreholes to a point intermediately between said boreholes;
d. circulating aqueous liquid through said zone that is rich in
water-soluble minerals to dissolve said minerals and forming a
fluid-filled cavern within the oil shale formation having a
predominantly areally extensive void space therein sufficient to
place the roof thereof in tension;
e. caving oil shale within the portions of said oil shale formation
communicating with said cavern into said cavern by circulating hot
fluid through the cavern along flow paths controlled to keep the
hot fluid in contact with the roof of the cavern;
f. flowing a kerogen-pyrolyzing fluid from one of said locations to
another through the cavern within the oil shale formation to effect
shale oil recovery from said oil shale adjoining and within said
cavern.
16. The method of claim 15 wherein the aqueous liquid in (c) is
water and the fluid in (e) is a kerogen-pyrolyzing fluid.
17. The method of claim 16 wherein the water is hot water and the
pyrolyzing fluid is steam.
18. The method of claim 17 wherein the water-soluble mineral is
nahcolite.
Description
BACKGROUND OF THE INVENTION
This invention relates to the recovery of hydrocarbons and
optionally water-soluble mineral from underground oil shale
formations containing water-soluble mineral deposits. Further, the
invention relates to hydrocarbon recovery by in-situ thermal fluid
extraction of oil shale within a fractured and/or rubblized portion
of a subterranean oil shale formation in and around a cavern and/or
interconnected cavities formed by leaching or dissolving, e.g.,
solution mining of the water-soluble minerals therefrom and
optionally recovering said minerals for suitable use in industry.
More particularly, it relates to oil recovery by in-situ retorting
and/or kerogen conversion within a caved-in or rubblized portion of
a subterranean oil shale formation in and around a cavern formed by
leaching or solution mining of water-soluble minerals therefrom,
such as nahcolite, trona, halite, mixtures thereof, etc.
DESCRIPTION OF THE PRIOR ART
Large deposits of oil in the form of oil shale are found in various
sections of the United States, and particularly, in Colorado and
surrounding states and in Canada. Various methods of recovery of
oil from these shale deposits have been proposed and the principal
difficulty with these methods is the high cost which renders the
recovered oil too expensive to compete with petroleum crudes
recovered by more conventional methods. The in-situ retorting or
conversion of oil shale to recover the oil contained therein is
made difficult because of the non-permeable nature of the oil shale
and the difficulty of applying heat thereto without extensive
mining or drilling operations. The mining and removal of the oil
shale for retorting of the shale in furnaces outside the formation
is commercially uneconomical in many cases.
In some subsurface oil shale formations such as in certain areas of
the Green River formation in the Colorado and surrounding areas of
the United States, such formations also contain water-soluble
minerals such as halite, nahcolite, trona, etc. in the form of
beds, lenses, nodules, iodes, veins, or the like. Such minerals can
be leached, dissolved and removed by suitable means such as
solution mining, e.g., by contacting such minerals with a solvent
such as an aqueous solution which may be neutral, alkaline or
acidic and recovering if desired, the mineral-containing solution
and at the surface extracting the minerals from the solution and
reusing the solution by recycling it back into the formation for
extracting more minerals from the underground formation or
dispersion of it if necessary. By treating such formations in this
manner permeability and voids are created and cavern formation and
rubblization of oil shale in the cavern can be induced from which
hydrocarbons can be recovered by suitable in-situ thermal
means.
The art discloses various means of removing hydrocarbons, e.g., oil
from oil shale as described, for example, in U. S. Pat. Nos.
3,400,762; 3,437,378; or 3,478,825 and also various means of
increasing permeability of oil shale formations are described in
U.S. Pat. Nos. 3,273,649; 3,481,398; and 3,502,372; or copending
applications Ser. No. 829,350, filed July 7, 1969, now abandoned;
or Ser. No. 770,964, filed Oct. 8, 1968, now abandoned and Ser. No.
75,009, filed Sept. 24, 1970 or Ser. No. 835,323, filed June 23,
1969 or Ser. No. 138,021, filed Apr. 28, 1971. Although these
references are directed to an advancement of the art, the basic
technique for recovering oil from oil shale still requires
rubblization techniques such as, by means of explosive devices,
e.g., nuclear energy which are expensive, difficult to control, and
presents a radioactive contamination problem, all of which are very
undesirable.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved method of
recovering hydrocarbons from a water-soluble mineral-containing oil
shale formation by leaching, dissolving or solution mining the
minerals so as to form a cavern and/or interconnected cavities
within the oil shale formation and simultaneously or sequentially
flowing a hot fluid into the top of the cavern so as to place the
roof under stresses of compression and/or tension and thereby
effecting spalling and rubblization of the oil shale and thermally
extracting and recovering hydrocarbons from the rubbled oil
shale.
It is an object of this invention to provide a method of recovering
hydrocarbons from oil shale by pretreating the formation by
solution mining water-soluble minerals to form a cavern within a
subterranean oil shale formation having a predominantly areally
extensive void space therein sufficient to place the roof thereof
under stresses of tension and/or compression.
It is a further object of this invention to provide an in-situ
retorting process for an oil shale formation pretreated by solution
mining water-soluble minerals so as to create or establish a cavern
therein and thereafter flowing a hot fluid near the top of the
cavern so as to place the roof of the cavern in tension to effect
caving-in oil shale in the vicinity of the cavern so as to
establish improved fluid flow channels through which the in-situ
retorting by a pyrolyzing fluid is conducted and thereby effect
improved oil recovery.
These and other objects are attained and hydrocarbons are
effectively recovered from oil shale formations containing deposits
of soluble minerals by leaching, dissolving or solution-mining the
minerals so as to establish interconnected voids or cavern having a
predominantly areally extensive void space therein sufficient to
place the roof thereof under stresses of compression and/or tension
to effect spalling and caving-in by rubbling oil shale within the
portions of the oil shale formation surrounding the cavern so as to
displace rubbled oil shale into the cavern and thereafter flowing a
kerogen-pyrolyzing fluid through the cavern to effect recovery of
shale oil from the formation. This may be effectively and
preferably accomplished by (a) determining the location of zones
rich in substantially water-soluble minerals within an oil shale
formation; (b) extending at least one well borehole into the
formation in communication with a zone rich in the soluble
minerals; (c) establishing fluid communication between at least one
well borehole and the soluble minerals at at least two spaced
locations within the zone rich in the soluble minerals; (d)
circulating a mineral dissolving or extracting fluid from one of
the borehole locations through the minerals therebetween, and out
the other of the borehole locations so as to dissolve the minerals
and form interconnected voids or a cavern within the oil shale
formation having a predominantly extensive void space therein
sufficient to place the roof thereof under stress; (e) caving-in
and rubbling oil shale within portions of the oil shale formation
surrounding the cavern by circulating hot fluid through the cavern
along flow paths controlled to keep the hot fluid in contact with
the roof of the cavern and place it under stress; and (f) flowing a
kerogen-pyrolyzing fluid from one of the borehole locations through
the cavern within the oil shale formation and out the other of the
borehole locations and recovering shale oil from the outflowing
fluid.
Water-soluble minerals present in the oil shale is meant to include
water-soluble silicates, halides, carbonates, and/or bicarbonates
salts, such as alkali metal (Na, K) chloride, carbonate,
bicarbonate and silicate, e.g., halite, trona, nahcolite and the
like.
The process of the present invention is so designed so as to create
a cavern or interconnecting cavities in the water-soluble mineral
beds(s) or zone(s) by dissolving, leaching or solution mining
techniques through at least one borehole penetrating said
formation. Leaching can be effected by cold or hot fluids or
solutions either at atmospheric or elevated pressures. When hot
solutions are used such as hot water or acidified hot water and/or
steam, more rapid dissolution is effected of certain water-soluble
minerals such as nahcolite, trona, halite to produce void spaces in
the oil shale formation thereby providing and enhancing well
communication, space for thermal expansion of the shale, and
greater surface for contact with subsequent pyrolyzing fluid. Water
can be cold or hot or steam or any other aqueous fluids can be used
such as steam and/or hot water containing acids, e.g., HCl, or HCl
+ HF, surfactants, sequestering agents, etc. If the initial
cavities are not in communication, fracturing may be necessary
using such means as hydrofracturing, explosive means, nuclear
means, etc., may be desirable. The leaching solutions can contain
chemical agents to enhance dissolution of the minerals. Under
certain leaching conditions decomposition of certain water-soluble
minerals, e.g., bicarbonates, into solublizing materials may take
place of such minerals as dawsonite and silicates which might be
present in the formation, thereby increasing the porosity of the
formation. For example, when nahcolite is dissolved with water, the
pH of the dissolution fluid is increased and thereby aids in the
dissolution of silicates, etc.
Leaching or solution mining of the water-soluble minerals such as
halite or nahcolite can be accomplished by a suitable solution
mining technique such as described in U.S. Pat. Nos. 2,618,475;
3,387,888; 3,393,013; 3,402,966; 3,236,564; 3,510,167 or Canadian
Pat. Nos. 832,828 or 832,276 or as described in copending
application Ser. No. 2,765 filed Jan. 14, 1970, now U.S. Pat. No.
3,596,992 Spalling and rubbling accomplished by hot fluid
circulation into the top of the cavern causing the oil shale walls
to spall, fracture, and rubble. In-situ thermal recovery of oil is
effected by a pyrolyzing fluid such as steam or mixtures of hot
water and steam or solvent extraction means.
The circulation of a pyrolyzing fluid into the top of the cavern
and/or through the cavern not only effects oil recovery but also
effects thermal rubbling and/or fracturization. Also, if the
pyrolyzing fluid such as steam is used to extract and recover oil,
more minerals may be dissolved perpetuating the process.
The term "kerogen-pyrolyzing fluid" is used to refer to a liquid or
gas which, by means of thermal, chemical and/or solvent action,
interacts with the kerogen components of the oil shale to produce
and entrain hydrocarbons, e.g., oil. Such a fluid may comprise
steam, hot hydrocarbons, hot gases, and/or mixtures of such fluids
with chemicals such as acids and/or organic solvents. The
kerogen-pyrolyzing fluid may be heated by surface or
borehole-located heating devices and/or by means of in-situ
combustion within the oil shale formation. The kerogen pyrolyzing
fluid may advantageously comprise or contain a solvent for the
soluble mineral, such as a steam condensate or a hot aqueous
solution of organic and/or inorganic acid, having a temperature,
such as at least several hundred degrees farenheit, such as from
about 450.degree. F to above about 1,500.degree. F and preferably
from about 550.degree. F to 1,000.degree. F. Where the
kerogen-pyrolyzing fluid forms aqueous components, its circulation
through the treated oil shale formation may enlarge the cavern, by
solution-mining the soluble mineral, while shale oil is being
produced. The injection of oxygen-containing gas to initiate and
sustain an underground combustion, to form a kerogen-pyrolyzing
fluid in situ, comprises a procedure for use in the present
invention.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a vertical sectional view, partly diagrammatic, of a
preferred embodiment of the invention;
FIG. 2 is a vertical sectional view of the treatment of the cavern
formed by leaching or solution mining of water-soluble minerals as
shown in FIg. 1;
FIG. 3 is a sectional view of an embodiment of the invention, the
formation being penetrated by a single well.
DESCRIPTION OF THE PREFERRED EMBODIMENT
It has been found that it is economically feasible to locate and
utilize a horizontally extensive zone of water-soluble mineral
within a relatively impermeable subterranean earth formation, such
as an oil shale formation.
As illustrated in FIG. 1, oil shale formation 12 contains a
generally horizontally extensive bed 13 of a continuous deposit of
a water-soluble mineral and nodules of minerals 12a, such as
halite, nahcolite or trona. Such mineral containing areas are
frequently encountered near the bottom of a layer of oil shale and
may be utilized to form cavities or caverns, in accordance with the
teachings of this invention, into which oil shale solids can be
moved by caving-in of the oil shale within formation 12.
In carrying out the method of this invention, the location of zones
rich in substantially water-soluble minerals may be determined by
geologic investigations based on an analysis of geophysical and
geochemical data. For example, the location and extent of such
zones may be determined by obtaining and correlating seismic, gamma
ray and/or density log data, core analysis data, etc. The borehole
of at least one well is extended into a zone containing a soluble
mineral and fluid communication between a surface location and at
least two spaced points within a substantially continuous and
generally horizontally extensive zone rich in soluble mineral is
established through the borehole or boreholes or the one or more
wells.
Fluid communication is thus established between at least two spaced
portions of well boreholes and the water-soluble minerals (as for
example, through perforations 22 through 23 of well boreholes 10
and 11, respectively, and the bed 13 of water-soluble minerals in
FIG. 1). The well boreholes 10 and 11 of FIG. 1 extend into the
soluble mineral bed 13 located within oil shale formation 12. The
fluid communication between well boreholes 10 and 11 and the bed 13
in water-soluble minerals therebetween may be established by
solution-mining a flow channel through the soluble mineral bed 13
and/or by means of conventional hydraulic, electric, and/or
explosive fracturing techniques, all well known in the art. Where,
for example, the subterranean stresses in and around soluble
mineral bed 13 are conducive to the formation of horizontal
fractures, the fluid communication between well boreholes 10 and 11
and the soluble minerals bed 13 may be established by a
conventional hydraulic fracturing technique.
Where the subterranean stresses are conducive to the formation of
vertical fractures, special steps are needed to form fractures that
will interconnect pairs of spaced wells with each other and the
soluble mineral. Such interconnecting fractures may be provided by
initially forming parallel vertical fractures in each of a pair of
wells. When at least one of the fractures is heated until it
becomes closed, by a thermally-induced swelling of the fracture
walls, a differently oriented vertical fracture is formed at a
higher temperature and pressure. Such fractures are then extended
until they intersect, and, the walls of the intersecting fractures
are leached, for example, in the zone of their intersection with
the soluble minerals. Such interconnected vertical fractures
provide flow channels for circulating a soluble mineral-extracting
solvent to form the caverns into which shale solids can be
displaced prior to or during the pyrolysis of the kerogen. Such
flow channels may be formed between a single pair of wells, to form
a test pattern which can subsequently be expanded, or may be formed
between all members of an extensive pattern of wells.
Alternatively, in similar tectonic environments, such
interconnecting fractures may be formed by a combination of steps
comprising (a) injecting a fluid through each of a pair of wells
into the soluble mineral-rich portion of the oil shale formation at
a pressure sufficient to form and extend generally vertical
fractures within the formation so that at least one pair of
generally vertical fractures are extended within the formation for
significant distances from the points of injection; (b) filling the
first-formed fracture in one of the wells with a fluid capable of
solidifying in situ to a compression-resistant solid and allowing
that fluid to solidify at substantially the pressure at which the
first-formed fracture was extended; and (c) injecting a fluid
through the well containing the so-plugged fracture at a pressure
sufficient to form and extend a second-formed generally horizontal
fracture through the oil shale formation until fluid injected
through this well is transmitted to the other one of the pair of
wells. Thus, by means of this procedure a low-cost fluid that is
capable of solidifying in-situ, e.g., a slurry of cement or a
solution of a resin, may be used to interconnect at least a pair of
wells thereby aiding in solution-mining and shale oil
production.
After fluid communication has been established between well
boreholes 10 and 11, aqueous leaching or solution-mining fluid
and/or liquid is injected down tubing string 24 and annulus outlet
30 in well borehole 10, out perforations 20 and 22, through bed 13
and up tubing string 25 and outlet 31 in well borehole 11 via
perforations 21 and 23. The aqueous fluid and/or liquid may
comprise water and/or steam or aqueous solutions of acid or
acid-forming materials and is circulated at pressures either above
or below the over-burden pressure. The circulating aqueous liquid
dissolves the water-soluble minerals and mineral by-products
thereof are recovered from the fluid flowing out of well borehole
11, for example, by conventional evaporation and/or precipitation
procedures. Thus, the solution-mining is preferably conducted by
injecting hot water or steam or mixture of steam and aqueous liquid
into the earth formation while producing fluids from the earth
formation at a rate such that most or all of the produced fluid is
liquid.
During the solution-mining operation described herein above, the
depths at which the circulating aqueous liquid is injected into and
produced from the earth formation are relatively immaterial as long
as fluid is flowed through the water-soluble bed 13.
The solution-mining is continued until the removal of water-soluble
material has created a cavern 32 (FIG. 2) having a significantly
large volume and areal extent and containing exposed oil shale
along its roof 33. Such a cavern 32 should extend over a
significant distance, such as at least about 50 feet or more along
at least one horizontal direction while extending over an area of
at least several hundred square feet and having a volume of at
least several hundred cubic feet. Thus, as illustrated in FIG. 2,
cavern 32 is formed within bed 13 extending to substantially the
top of underlying formation 19 and the bottom of overlying oil
shale formation 12.
Oil shale 34 (FIG. 2) from roof 33 is caved into the cavern 32 and
the cavern roof 33 is migrated up within the oil shale formation 12
by circulating a kerogen-pyrolyzing fluid through the cavern 32.
The circulation of such a fluid is controlled by adjusting the
points of injection and production and the temperature and pressure
of the circulating fluid so that the roof 33 of the cavern 32 is
contacted by kerogen-pyrolyzing fluid at a temperature at which
significant amounts of the kerogen in the oil shale 34 are
converted to fluid and removed from the cavern 32. In the initial
stage this can be accomplished by injection down annulus outlet 30
and tubing string 24 of well borehole 10, through cavern 32 into
contact with the roof 33 thereof, and into well borehole 11 and out
the annulus outlet 31 thereof.
Such a fluidization of kerogen tends to fracture the oil shale 34
since it both increases the volume of at least one component within
the normally impermeable oil shale 34 and removes a significant
proportion of solid material from the oil shale 34. In oil shale,
the kerogen tends to be concentrated along layers such as bedding
planes, and the effects of such kerogen fluidizing and removing
actions tend to be localized, e.g., along the layers.
In the present process, the rate of the fracturing, flaking, or
spalling of oil shale material into the cavern 32 is increased by
the fact that the oil shale 34 being treated is under stresses of
compression and/or tension along the roof 33 of cavern 32. The
caving of oil shale 34 into the cavern 32 is further enhanced by
controlling the circulating kerogen-pyrolyzing fluid so that the
roof-contacting portion has a temperature above 450.degree. F and
preferably between 550.degree. and 850.degree. F at which kerogen
is pyrolyzed at a relatively rapid rate. Since heat is transferred
within the oil shale 34, the heat causes portions of kerogen which
are surrounded by impermeable oil shale material to be converted to
a liquid or vapor at pressures that fracture the surrounding oil
shale material. Since this material is under stress (tension or
compression) the fractured portions separate and cave into the
cavern 32. Such a caving is further enhanced when the roof is
contacted with an aqueous fluid, such as steam or hot aqueous
liquid, that tends to dissolve and remove water-soluble material
35, such as entrapped or dispersed halite, nahcolite, or the like,
from within the oil shale formation 12. The dissolving and removing
of solid material is beneficial in both enhancing the caving and
creating additional void space into which additional amounts of oil
shale can be caved.
As the roof of the cavern 32 is migrated upward within the oil
shale formation 12, the depth at which the circulating
kerogen-pyrolyzing fluid is injected is preferably raised to keep
it near the roof 33 of the cavern 32. This causes the roof 33 to be
contacted by the hottest and most dilute incoming portions of the
fluid. By similarly raising the depth of the points at which fluids
are produced from the cavern 32, the circulating fluid is caused to
flow along the roof 33 of the cavern 32 as a stream that flows over
the top of a body of substantially static fluid within the cavern
32. The tendency to form such a flow path is enhanced when the
circulating fluid is heated at a surface location or within well
borehole 10 prior to its injection into the cavern 32. This causes
the incoming fluid to be hottest and less dense than the fluid in
the lower portion of the cavern 32. Such an effect is further
enhanced by circulating a vapor-containing hot fluid, such as
steam, hot gas, or a mixture of steam or hot gas and a liquid. The
cavern 32 extends substantially to the top of oil shale formation
12.
The kerogen-pyrolyzing fluid continues to be circulated from well
borehole 10 through the cavern 32 of oil shale formation 12 and out
of well borehole 11 in the manner discussed hereabove with respect
to FIG. 1. Hydrocarbons are continuously recovered from the heated
fluid circulating out of well borehole 11 by means well known in
the art.
Thus, as illustrated in FIG. 1, conventional equipment and
techniques, such as heating means, pumping means, separators and
heat exchangers may be used for pressurizing, heating, injecting,
producing, and separating components of the heated fluid
circulating through the cavern 32 within oil shale formation 12.
The production of the fluid may be aided by downhole pumping means,
not shown, or restricted to the extent necessary to maintain the
selected pressure within the oil shale formation 12.
The fluid circulated through cavern 32 to recover hydrocarbons from
oil shale formation 12 may comprise any heated fluid and/or liquid,
such as hot gases, hot water, and mixtures thereof. Oil shale
reactive properties may also be imparted to the circulating fluid
as discussed hereinabove.
Numerous methods are known and available to those skilled in the
art for arranging conduits in the portions of the well boreholes
that are adjacent to such water-soluble zones and the overlying oil
shale so that (a) fluids can be injected and produced at
increasingly shallower depths and (b) the well conduits are
unaffected by the collapsing of the earth formations.
As shown in FIG. 1 of the drawing, the well boreholes may be
suitably arranged by casing such portions of the well boreholes and
cementing the casings at locations above and below the intervals to
be treated. Such casings are preferably equipped with means, such
as slidable and/or collapsible elements, for avoiding buckling or
overstressing due to thermally induced expansion or contraction.
Such casings may be perforated along the interval to be exploided
at substantially any convenient time with substantially any density
of openings.
In using the illustrated well equipment, the treatment of the
water-soluble zone may be started prior to casing or fracturing the
wells, for example, by underreaming the well boreholes and/or
jetting fluid into the water-soluble zone to radially extend a
notch around the well. After the wells have been cased and
perforated, they are preferably fractured in order to establish an
interwell communication through fracture paths. Numerous procedures
are known and available for accomplishing such fracturing and
various suitable procedures are described in my copending patent
application and the applications referred to therein.
The solution-mining operation is preferably conducted by
circulating hot fluid or aqueous liquid through a
well-interconnecting flow path. The flow of a hot fluid, e.g.,
steam or aqueous fluid, tends to be confined within the
water-soluble zone even if intercommunicating fractures have
extended into the overlying oil shale. Within the oil shale, the
fractures tend to be closed by the thermal swelling of the fracture
walls. Within the water-soluble zone, such a closure is prevented
by the dissolving of the wall material.
After forming cavern 32 along the bottom of the oil shale, the roof
33 of the cavern 32 is migrated up within the oil shale by
circulating a kerogen-pyrolyzing fluid along the roof 33 of the
cavern 32. The kerogen-pyrolyzing fluid may be the same fluid used
in the solution-mining operating and roof-migrating operations may,
to some extent, be concurrent.
The migration of the cavern roof 33 up within the oil shale
formation 12 forms a fracture-permeated zone that may contain a
significant amount of recoverable hydrocarbons. Hydrocarbons may be
recovered from this zone by substantially any oil shale pyrolyzing
procedure such as an in-situ combustion, hot fluid heating, or the
like type of subterranean retorting procedure. Beyond the areal
extent of the cavern 32, the oil shale 34 tends to remain
impermeable and thus tends to confine any fluids which are being
circulated through the fracture-permeated zone.
A single well system shown in FIG. 3 may be utilized by a dual zone
completion arrangement such that fluids can be injected at one
point of the well and produced from another point of the same well.
This fluid communication can be established in one borehole between
at least two spaced portions of the well borehole and the
water-soluble minerals (as for example, in FIG. 3 communication is
through the tubing string the ends of which are open to the
water-soluble minerals and some distance apart.) Thus a single well
may be utilized by a dual zone completion arrangement as shown in
FIG. 3 such that fluids can be injected at one point of the well
and produced from another point of the same well. In FIG. 3, the
welbore is 40, the casing is 41, the sealant is 47, within the
casing are the injection tubing string 43 and production tubing
string 44, the borehole 40 penetrates oil shale formation 9 with
mineral zone(s) 10 or multizones 10b and 10c and mineral nodules
48.
Fracturing pressures are generated within the oil shale formation 9
while lower pressures are maintained within the cavern 45 which is
formed within oil shale formation 9 by the removal of the
water-soluble minerals. These pressures are preferably generated by
merely circulating hot fluid through cavern 23a. As the roof of the
cavern 45 is heated kerogen is pyrolyzed within the cavern walls
and the pressures of the pyrolysis products increase until portions
of the walls are spalled into the cavern 45 creating a rubblized
zone 24a and surrounding fracture area 46.
In summary, then, well boreholes are opened into at least two
horizontally spaced points within such a water-soluble zone and are
equipped to convey fluids between that zone and at least one
surface location. Fluid circulation is established between the
spaced points within the soluble zones. An aqueous fluid is
circulated through that zone in order to solution-mine a cavern
having a roof along which oil shale is exposed. The cavern is
extended to form a void space having horizontal dimensions
sufficient to create a tensile stress, due to the tendency of the
roof to sag, and to have a volume sufficient to accommodate a
significant amount of solid material. Oil shale is caved into the
cavern by circulating a kerogen-pyrolyzing fluid through the cavern
at a temperature at which kerogen in the oil shale is converted to
fluid material that is extracted and removed by the circulating
fluid. The depths and rates at which the circulating fluid is
injected into and produced from the cavern are adjusted to maintain
a flow along the roof as the roof migrates up within the oil shale
formation.
EXAMPLES
(A) A single injection-production well was designed properly
insulated to penetrate a nahcolite rich oil shale formation and
through the injection tubing hot water was injected into the
nahcolite bearing formation for about a week to leach out the
nahcolite as an aqueous solution which was recovered above ground
via the production tubing. The size of the cavern thus produced was
determined by conventional means such as measuring the
concentration of the salt in solution and thereafter steam at a
temperature above 500.degree. F was injected along the roof of the
cavern to effect roof stress resulting in rubbling and spalling of
the oil shale into the cavern and cavern enlargement. Steam
injection along the cavern roof was continued as well as through
the rubbled oil shale bed at a temperature between 550.degree. F
and 850.degree. F effecting kerogen decomposition to hydrocarbons
which were recovered via the production tubing where the
hydrocarbons were separated above ground from the condensed steam
by conventional means.
(B) The procedure as described in (A) was repeated except that
instead of using hot water to leach out the nahcolite steam was
used. Thus, once the cavern was formed by steam leaching out the
nahcolite, steam injection was continued under controlled
conditions so that its flow path was directed along the roof of the
cavern placing it under stresses of tension and compression
producing results as noted in (A). Thereafter a portion or the
entire steam injection flow was directed to flow through the
rubbled oil shale to effect kerogen decomposition and hydrocarbon
recovery as noted in (A).
Other than steam flow control and direction the (B) process can be
regarded as a single process operation in which steam is used as
the leaching, rubbling and hydrocarbon recovery agent provided
temperature, pressure and flow control of the steam as described in
(B) is carefully controlled in accordance with the teaching of the
present invention.
The method described hereinbelow of caving oil shale into a void
space within a subterranean oil shale provides the advantages of
(1) converting at least some of the kerogen to hydrocarbon products
that can be recovered and sold while the process is being operated,
(2) converting at least some of the kerogen to fluid that can be
used to form a part or all of a kerogen-pyrolyzing fluid that is
circulated to operate such a process, and (3) caving the oil shale
above an areally extensive void space which was formed by a
solution-mining process, (that produced a valuable by-product) and
thus converting the relatively impermeable oil shale into rubble
from which shale oil can be recovered.
* * * * *