U.S. patent number 3,858,654 [Application Number 05/371,204] was granted by the patent office on 1975-01-07 for hydraulic mining technique for recovering bitumen from subsurface tar sand deposits.
This patent grant is currently assigned to Texaco Inc.. Invention is credited to Clarence O. Walker.
United States Patent |
3,858,654 |
Walker |
January 7, 1975 |
HYDRAULIC MINING TECHNIQUE FOR RECOVERING BITUMEN FROM SUBSURFACE
TAR SAND DEPOSITS
Abstract
A method for recovering bituminous petroleum from tar sand
deposits by hydraulic mining. In one illustrative embodiment, an
injection string having horizontally oriented nozzles on the lower
end thereof and provided on the surface with means for rotating the
injection string simultaneous with injecting fluids down the
injection string. A separate flow path for recovery of the injected
fluid with bitumen mixed therewith to the surface of the earth is
also provided, which may be the annulus between an outer casing
with the rotatable injection string in the center thereof. The
fluid used in conjunction with this solution-mining technique is an
aqueous solution of a polyphosphate wetting agent plus an
alkalinity agent, heated to a temperature greater than the
temperature of the tar sand deposit. The bituminous petroleum is
separated from the phosphate solution by contacting the fluid with
a hydrocarbon fluid such as diesel oil.
Inventors: |
Walker; Clarence O. (Richmond,
TX) |
Assignee: |
Texaco Inc. (New York,
NY)
|
Family
ID: |
23462959 |
Appl.
No.: |
05/371,204 |
Filed: |
June 18, 1973 |
Current U.S.
Class: |
166/272.6;
166/303 |
Current CPC
Class: |
E21B
43/281 (20130101); F02B 3/06 (20130101) |
Current International
Class: |
E21B
43/28 (20060101); E21B 43/00 (20060101); F02B
3/00 (20060101); F02B 3/06 (20060101); E21b
043/24 (); E21b 047/00 () |
Field of
Search: |
;166/250,267,275,272,303,35R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Purser; Ernest R.
Assistant Examiner: Ebel; Jack E.
Attorney, Agent or Firm: Whaley; Thomas H. Ries; C. G.
Claims
I claim:
1. A method for recovering bitumen from a subterranean tar sand
deposit having injection means and production means comprising:
contacting the tar sand deposits with an aqueous solution
comprising an inorganic polyphosphate substance plus an alkalinity
agent, the temperature of said solution being at least as great as
the temperature of the tar sand deposit.
2. A method as recited in claim 1 wherein the aqueous polyphosphate
solution is made to contact the tar sand by jetting action.
3. A method as recited in claim 1 wherein the injection means is at
least one well contining an injection string for introducing the
polyphosphate solution into the tar sand deposit.
4. A method as recited in claim 3 wherein the injection string is
equipped on its lower end with at least one horizontally oriented
nozzle.
5. A method as recited in claim 3 wherein surface means are
provided for rotating the injection string and said string is
rotated while the polyphosphate solution is being injected.
6. A method as recited in claim 4 wherein the annular space between
the injection string and well casing is used for production
means.
7. A method as recited in claim 1 wherein the polyphosphate is a
water soluble salt of pyrophosphoric acid.
8. A method as recited in claim 7 wherein the polyphosphate is a
sodium acid pyrophosphate.
9. A method as recited in claim 7 wherein the polyphosphate is
sodium trihydrogen pyrophosphate.
10. A method as recited in claim 7 wherein the polyphosphate is
trisodium hydrogen pyrophosphate.
11. A method as recited in claim 7 wherein the polyphosphate is
tetrasodium pyrophosphate.
12. A method as recited in claim 7 wherein the polyphosphate is a
potassium salt of pyrophosphoric acid.
13. A method as recited in claim 7 wherein the polyphosphate is the
lithium salt of pyrophosphoric acid.
14. A method as recited in claim 1 wherein the polyphosphate is a
water soluble tripolyphosphate salt.
15. A method as recited in claim 14 wherein the phosphate is
pentasodium tripolyphosphate.
16. A method as recited in claim 1 wherein the concentration of
polyphosphate is at least 0.10 percent by weight.
17. A method as recited in claim 1 wherein the concentration of
polyphosphate is from 0.10 percent to about 5.0 percent by
weight.
18. A method as recited in claim 1 comprising the additional step
of contacting the mixture of bitumen and polyphosphate solution
with a hydrocarbon fluid to promote separation of bitumen from the
aqueous polyphosphate solution.
19. A method as recited in claim 18 wherein the hydrocarbon fluid
is diesel oil.
20. A method as recited in claim 1 wherein the alkalinity agent is
selected from the group consisting of sodium hydroxide, lithium
hydroxide, potassium hydroxide and ammonium hydroxide.
21. A method as recited in claim 20 wherein the alkalinity agent is
sodium hydroxide.
22. A method as recited in claim 1 wherein the concentration of
alkalinity agent is from about 0.10 to about 5.0 percent by
weight.
23. A method as recited in claim 1 wherein the polyphosphate
solution is injected via the injection means and the injection
pressure is increased gradually with time to a value in pounds per
square inch not exceeding the over-burden thickness in feet.
24. A method as recited in claim 1 wherein the production rate of
bitumen is monitored continually and the injection pressure is
increased in response to a decrease in bitumen production rate.
25. A method as recited in claim 1 wherein the polyphosphate
solution is heated to a temperature of from around 100.degree. to
about 200.degree. F.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to a method for recovering bitumen from
subterranean tar sand deposits by hydraulic-mining, especially
applicable to tar sand deposits not amenable to strip mining
because the overburden thickness is too great.
2. Description of the Prior Art
Petroleum is found in subterranean formations or reservoirs in
which it has accumulated, and recovery of conventional petroleum is
achieved by penetrating these reservoirs with wells and permitting
the fluid to flow to the surface as a result of natural pressure
existing in the reservoir, or by pumping the fluid to the surface
in some instances where insufficient natural pressure exists to
force it to flow to the surface. There are many
petroleum-containing reservoirs which contain hydrocarbon which is
too viscous to be pumped from the reservoir under normal
circumstances. When such reservoirs are encountered, production is
possible only by means of some process of supplemental recovery,
commonly referred to as secondary or teritary recovery, in which
energy is supplied to the reservoir to force the petroleum to move,
or heat and/or a solvent is supplied to the reservoir to reduce the
viscosity of the petroleum.
The most extreme example of formations which contain petroleum too
viscous to recover by conventional means are the so-called tar
sands or bitumen sands, such as those located in the Western United
States, Western Canada, and Venezuela. These formations are known
to contain huge reserves of bituminous petroleum, but the
bituminous petroleum contained therein is too viscous to be
recoverable by conventional techniques.
The present state of the art for the recovery of bitumen from tar
sand deposits can be generally classified as strip mining or in
situ separation. Strip mining requires removal of the overburden by
mechanical means and the mixture of bitumen and sand that
constitutes the tar sand deposit is then similarly removed by
mechanical means and transported to a surface processing plant for
separation of bitumen and sand. In situ separation processes make
use of techniques for separating the bitumen from the sand within
the tar sand deposit itself, so the bitumen in some modified form
may be transported to the surface with the sand left in the tar
sand deposit. Techniques presently employed for insitu separation
may be classified as thermal or emulsification processes. The
thermal techniques include in situ combustion, (fire flooding), and
steam flooding. Emulsification processes also involve the use of
steam plus some additional chemical to promote emulsification of
the high viscosity bitumen so that it may be transported to the
surface where the emulsion is resolved into bitumen and water.
Although many in situ separation techniques have been proposed in
the prior art, none have been both economically and technically
successful.
Most known in situ processes involve injection of fluid under
fairly high pressures. Injection of high pressure fluid can be
conducted safely only if the formation overburden thickness is
great enough to contain the pressure without rupturing. Strip
mining of a tar sand deposit is economically feasible only if the
ratio of overburden thickness to tar sand deposit thickness is
around one or less. Many deposits exist wherein the overburden
thickness is too great to permit exploitation by strip mining, and
not great enough to contain high pressure fluids.
In view of the foregoing, it can be appreciated that there is a
substantial, unfulfilled need for a method for recovery of
bituminous material from tar sand deposits, particularly those
deposits which are not suitable for strip mining or for in situ
recovery processes involving injection of a high pressure
fluid.
BRIEF DESCRIPTION OF THE DRAWING
The attached drawing illustrates in cross-sectional view both the
surface and subsurface equipment and completion for application of
my process for hydraulic-mining of tar sand deposits.
SUMMARY OF THE INVENTION
I have discovered, and this constitutes my invention, that bitumen
may be recovered from subterranean tar sand deposits by a
hydraulic-mining technique wherein the tar sand is contacted by a
hot, aqueous polyphosphate solution containing an alkaline
substance such as caustic or sodium hydroxide. One means for
accomplishing this process employs a rotating injection string
equipped on its lower end with jet nozzles so that the fluid may be
directed as a jet stream against the tar sand deposit face. A
separate communication path to the surface of the earth facilitates
movement of the injected fluid with bitumen dispersed therein to
the surface for further processing. The injection string is
constructed so as to permit its rotation as the fluid is being
injected down the injection string and out through the jet nozzles
on the end thereof, so that a stream of fluid sweeps the tar sand
deposits. Polyphosphate wetting agents suitable for use in my
invention include sodium trimetaphosphate and sodium
tetrametaphosphate. The bituminous petroleum is then separated from
the polyphosphate solution by contacting same with a hydrocarbon
fluid such as diesel oil.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
My invention can be best understood by a reference to the attached
drawing, in which a tar sand deposit 1 is located at too great a
depth for economical strip mining and not deep enough to permit
thermal recovery by high pressure fluid injection. A combination
injection production well 2 is drilled to the bottom of the tar
sand deposit, and casing 3 is set to the top of the formation. A
separate injection string 4 is run inside the casing 3, to a point
near the bottom of the tar sand deposit. The injection string 4 is
equipped with nozzles 5 near the bottom thereof, and the completion
equipment on the surface includes means for rotating the injection
string as fluid is pumped down the string. This is illustratively
embodied in the drawing by motor 6 coupled to injection string 4,
and sealing devices 7 and 8 which insure a fluid-tight connection
between the rotating and nonrotating portions of the surface
equipment. A pump 9 pumps the hot alkaline polyphosphate solution
down the injection string with sufficient pressure to provide the
jetting action and insure contact with the tar sand essential to
the proper functioning of my process.
A separate flow channel for returning a mixture of solvent and
bitumen to the surface of the earth is also provided. This may be
in the form of a separate well, or the annular space 10 between
casing 3 and injection string 4 in the drawing may be utilized for
this purpose. On the surface, fluid conduit 11 is connected to
annular space 10 on one end and on the other end to separation tank
12. Separation tank 12 which may be equipped with a mixing device
and heater has connected thereto flow line 13 which is connected to
the output of pump 14 which takes suction from hydrocarbon treating
fluid tank 15. Polyphosphate solution make up tank 16 is connected
via pump 9 to the top of injection string 1.
In operation, the alkaline aqueous polyphosphate solution is pumped
from supply tank 16. It is not necessary to inject the hot
polyphosphate solution with as high pressure at the start as will
be required later in the process since the solution jet will only
have to travel a relatively short distance before contacting the
face of the tar sand deposit. The hot polyphosphate solution is
injected via string 4 under pressure and out through nozzle 5
against the face of the tar sand deposit. The bitumen is contacted
by the hot polyphosphate solution, and aided by the high velocity
of the fluid jet 17, bitumen coated sand is readily dislodged from
the tar sand formation. Emulsification does not occur, and much of
the sand settles to the bottom of the cavity in the tar sand
deposit. Some sand, particularly the fine grain sand, may be
produced to the surface.
As bitumen and some sand are removed from the tar sand deposit, a
cavity is created adjacent to the nozzles on injection string 4,
and the size of this cavity increases with time as is illustrated
on the drawing with dashed time contour lines which are designated
T.sub.1, T.sub.2, and T.sub.3. As the cavity increases, it is
necessary to increase the injection pressure so that the jet stream
17 will reach to the cavity walls with sufficient veolcity to
dislodge bitumen coated sand.
Throughout the process of my invention, a mixture of bitumen and
hot polyphosphate solution, with a minor amount of sand suspended
therein, flows back to the surface of the earth via the
communication path provided therefor by annulus 10 in the example
illustrated in the drawing. The produced bitumen-polyphosphate
solution mixture passes via flow line 11 into separation tank 12.
Hydrocarbon treating fluid such as diesel oil contained in tank 15
is pumped via pump 14 into tank 12 to cause separation of bitumen
and sand. Sand settles to the bottom and is removed mechanically
via line 18. Bitumen and hydrocarbon treating fluid separate into a
top phase and is removed by line 19 and then to surface processing
equipment. Hot polyphosphate solution constitutes the third phase,
passing via line 20 back to tank 16 where it can be recycled into
the injection string 4.
The filud injected in the form of a jet and preferably a rotating
jet, is an aqueous alkaline solution of a polyphosphate such as
tetrasodium pyrophosphate Na.sub.4 P.sub.2 O.sub.7, sodium acid
pyrophosphate Na.sub.2 H.sub.2 P.sub.2 O.sub.7 or pentasodium
tripolyphosphate, plus an alkalinity agent such as caustic soda
(sodium hydroxide, NaOH).
Polyphosphates are inorganic salts whose anions contain PO.sub.4
units linked by sharing oxygens with other tetrahedra. The
polyphosphates may be in chain form, e.g., [P.sub.2 O.sub.7
].sup.4.sup.-, or [P.sub.3 O.sub.10 ].sup.5.sup.-, or in a ring
form [P.sub.3 O.sub.9 ].sup.3.sup.- and [P.sub.4 O.sub.22
].sup.4.sup.-, tri- and tetra-metaphosphates respectively.
Polyphosphates are hydrophilic surface active agents as opposed to
organic wetting agents which may be considered hydrophobic surface
active agents. There are no oleophilic moieties present in
inorganic polyphosphates so they are not surfactants in the sense
of alkyl or alkylaryl sulfates, sulfonates or phosphates. The prior
art teaches the use of polyphosphates as builders in house-hold
detergents, and that polyphosphates function as defloculants in
drilling fluids and other suspensions, and for the purpose of
forming soluble complexes.
Any water soluble salt of pyrophosphoric acid, H.sub.2 P.sub.2
O.sub.7 may be used in the process of my invention. For example,
the sodium, potassium or lithium salt of pyrophosphoric acid may be
used. There are usually more than one salt for each cation known.
For example, the sodium salts are tetrasodium pyrophosphate,
Na.sub.4 P.sub.2 O.sub.7, trisodium hydrogen pyrophosphate,
Na.sub.3 HP.sub.2 O.sub.7, disodium pyrophosphate (known
commercially as sodium acid pyrophosphate) Na.sub.2 H.sub.2 P.sub.2
O.sub.7, and sodium trihydrogen pyrophosphate, NaH.sub.3 P.sub.2
O.sub.7.
Other sodium polyphosphates such as pentasodium tripolyphosphate,
Na.sub.5 P.sub.3 O.sub.10 are also known and may be used in my
process. Ring polyphosphates such as sodium trimetaphosphate
Na.sub.3 (PO.sub.3).sub.3 and sodium tetrametaphosphate Na.sub.4
(PO.sub.3).sub.4 may also be used.
Generally the preferred materials are the water soluble salts of
pyrophosphoric acid, and especially sodium acid pyrophosphate or
tetrasodium pyrophosphate.
The concentration of polyphosphate in the aqueous solution may be
quite dilute, as low as 0.052-2 percent. Although concentrations
greater than this may be used, there is no particular advantage in
using larger concentrations, and while the cost of the material is
low, economics of the process are optimized by using the lowest
effective concentration.
Ordinarily an alkalinity agent will be added to the polyphosphate
solution. Care should be taken to insure that the cation associated
with the alkalinity agent does not form an insoluble salt with the
particular polyphosphate being used. Generally sodium hydroxide is
the preferred material, although potassium hydroxide, lithium
hydroxide or ammonium hydroxide may be used also.
Sufficient alkalinity agent should be added to the solution to
bring the pH thereof to a value above 10 and preferably above 12.
Generally 0.1-5.0 percent by weight will be sufficient. One
convenient means for maintaining the desired pH is to add
approximately equal amounts of the alkalinity agent and the
polyphosphate.
Heating the aqueous alkaline polyphosphate to a temperature in
excess of the natural formation temperature will increase the
effectiveness of this hydraulic solution mining technique. The
solution may be heated on the surface just prior to injecting it
into the injection means. The preferred operating temperature is
from about 100.degree.F. to about 200.degree.F.
One attractive feature of the process of my invention is the fact
that bitumen is not emulsified on being contacted with the hot
aqueous alkaline polyphosphate solution. Bitumen is removed
effectively from the sand but remains in a separate phase which
will form a discrete layer distinct from the aqueous solution if
agitation is stopped. The bitumen may be pumped to the surface
leaving most of the polyphosphate solution in the cavity formed in
the subterranean tar sand formation if desired.
Much of the sand from which the bitumen is removed settles to the
bottom of the cavity, eliminating the need for handling large
amounts of sand on the surface. Some sand may be carried to the
surface along with the bitumen, but the bulk of the sand will
remain in the cavity in the subterranean formation.
As the distance from the injection point to the face of the cavity
increases, the injection pressure should be increased so that the
fluid jet will continue to contact the cavity wall. The injection
pressure should not be raised to the point where fracture of the
overburden will result. As a general rule, the pressure in pounds
per square inch should not exceed the overburden thickness in feet.
Eventually the cavity size will become so great that the fluid
stream no longer reaches the cavity wall. Some additional bitumen
recovery may be possible by pumping all fluid from the cavity so
the injected fluid can reach greater distances from the injection
nozzle. The end point of the process is easily detected on the
surface by a decline in the rate of bitumen production.
Separation of bitumen and aqueous solution occurs quickly when
agitation is stopped. Separation speed and efficiency is enhanced
by contacting the mixture with a hydrocarbon separation fluid, such
as diesel. The separation fluid may be added continuously or
intermittenly, on the surface or in the tar sand formation.
Field Example
A tar sand deposit is to be exploited and it is determined that the
thickness of the tar sand deposit is 50 feet and the thickness of
the overburden is 125 feet. Since the ratio of overburden thickness
to tar sand deposit thickness is greater than 1, strip mining is
ruled out on economic basis. A well is drilled to the bottom of the
deposit and a casing is set to the top portion of the tar sand
deposit. A tubing string is inserted into the casing, the bottom
portion of the tubing string being equipped with two horizontally
oriented jet nozzles so that fluids pumped into the tubing string
will exit through these nozzles in a generally horizontal direction
with considerable velocity. The injection string is equipped on the
surface with means for rotating the injection string by an electric
motor, and sealing devices to establish a liquid tight seal between
the rotating and nonrotating members are also provided. An aqueous
solution of 0.3 percent sodium acid pyrophosphate and 0.3 percent
sodium hydroxide heated to a temperature of 150.degree. F. is
injected into the injection means by a pump located on the surface.
Initially the injection pressure is approximately 50 pounds per
square inch, since the jet emerging from the nozzles must flow only
a short distance before it impinges against the tar sand deposits.
The mixture of bitumen from the tar sand and the polyphosphate
solution is produced to the surface via the annular conducting
space between the rotating injection string and the casing. The
produced mixture is passed to a separation tank located on the
surface, and diesel oil is added to the mixture to aid in rapid
separation.
As the cavity increases, the solvent jet streams from the nozzles
on the end of the injection string must travel further away from
the injection point before contacting the wall of the cavity in the
tar sand deposit, and so the injection pressure must be increased.
The need for an increase in injection pressure is determined by
monitoring the concentration of bitumen in the
bitumen-polyphosphate solution mixture being produced to the
surface of the earth. A decrease in the concentration of bitumen in
the produced fluid indicates that the jets of polyphosphate
solution are not moving sufficiently far away from the nozzles to
contact virgin tar sand, and so the injection pressure must be
increased. The injection pressure is increased slowly since it is
not desired to create a fracture between the pressurized tar sand
formation and the surface of the earth which would establish an
undesired return communicating path through the overburden to the
surface. By increasing the injection pressure in small increments,
e.g., 5 or 10 psi at a time, the injected solvent stream may be
made to continually contact the outer cavity walls within the tar
sand deposit. The injection pressure expressed in pounds per square
inch is not allowed to exceed the overburden thickness expressed in
feet. This process is continued until a substantial decrease in
bitumen content of the produced bitumen-containing fluid is
evidenced, and an increase in injection pressure up to 125 psi
fails to cause a corresponding increase in the bitumen content of
the produced fluid. This indicates that the maximum range of the
polyphosphate fluid jet within the cavity has been reached and no
additional bitumen can be recovered by this technique from the
cavity.
After it has been determined that the solution-mining process has
been extended as far into the tar sand deposit as possible, the
polyphosphate solution remaining within the cavity may be recovered
for reuse in adjacent areas of the deposit by pumping the fluid
from the cavity.
EXPERIMENTAL
In order to verify the operability of my invention and further to
determine the optimum values for the controllable parameters, the
following experimental work was performed.
One hundred gram samples of tar sand obtained from the Athabasca
area in Alberta, Canada were compressed into cylindrical cakes at
6,000 pounds per square inch pressure. The samples were placed in
an open container filled with the various test solutions. A motor
driven mixer blade was positioned in the solution approximately 1
1/2 inches from the face of the tar sand cake and rotated. The
extent of disintegration of the tar sand at the end of 15 minutes
was observed and this observation is reported below. In all cases
the temperature was maintained at 125.degree.-130.degree.F.
TABLE I ______________________________________ Cake Condition at
Fluid End of 15 Minutes ______________________________________ 1.
tap water unchanged 2. water +0.3% Sodium Acid Pyro Phosphate
unchanged 3. water +0.3% caustic soda 50% disintegrated 4. water
+0.3% caustic soda +0.3% sodium acid pyrophosphate 100%
disintegrated 5. water +0.6% caustic soda +0.6% sodium acid
pyrophosphate 100% disintegrated 6. water +0.3% sodium acid
pyrophosphate + NH.sub.4 OH to yield pH of 10.8 slight
disintegration ______________________________________
After disintegration of the tar sand samples, the mixtures were
allowed to settle. Clean sand settled to the bottom and distinct
layers of bitumen and polyphosphate solution formed. Only a slight
amount of hydrocarbon was suspended in the aqueous polyphosphate
solution. Addition of diesel oil to the mixture solubulized the
dark material, which floated to the surface and was easily
separated. There appeared to be no emulsion formation.
While my invention has been described in terms of a number of
specific illustrated embodiments, it is not so limited, and many
modifications thereof will be apparent to those skilled in the
related art without departing from the true spirit and scope of my
invention. Furthermore, it is not my intention to be bound by any
particular explanation of the mechanism responsible for the
benefits resulting from application of the process of my invention.
It is my intention that my invention be limited only by such
restrictions and limitations as may be imposed by the appended
claims.
* * * * *