IN SITU RECOVERY OF VISCOUS MATERIALS

EXTRACTION DE MATIERES VISQUEUSES SUR CHANTIER D'EXPLOITATION D'UN GISEMENT

English Abstract

Case 5554
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1.0/12/81


ABSTRACT OF THE INVENTION


Viscous materials, such as bitumen, can be recovered
from subsurface earth formations, such as tar sands, by
forming a shaft or first borehole to the base of the
desired subsurface formation, extending the borehole into
the underburden, drilling second boreholes upwardly and
radially into the formation, injecting steam into these
boreholes until the temperature of parts of the formation
is such that the viscosity of the material is reduced, and
collecting the liberated material. Variations of this
basic procedure are discussed.

Claims

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The embodiments of the invention in which an exclusive
property or privilege is claimed are defined below.

CLAIMS
1. A method for the in-situ recovery of viscous
materials from a subsurface formation, comprising:
a) forming a first borehole to the base of the
subsurface formation to be exploited,
b) extending the borehole below the base of the
formation,
c) drilling a plurality of second boreholes
extending substantially upwardly and radi-
ally outwardly into said formation from the
lower portion of the borehole of step (b),
d) injecting steam into said second boreholes,
with the steam having a pressure above the
fracture pressure of the subsurface forma-
tion,
e) maintaining the injection of step (d) for a
time period so as to increase the tempera-
ture of that portion of the formation
surrounding said second boreholes and any
fracture fissures formed by the injection,
f) releasing the pressure on the system of
second boreholes, thus allowing any lib-
erated material of reduced viscosity to move
to the lower portions of said second bore-
holes and thence to the lower portion of the
first borehole,

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g) collecting the liberated material, and
h) repeating the injection/production cycle of
steps d-g.

2. The method of Claim 1 wherein
a) the subsurface formation containing viscous
materials is approximately 30 meters or more
below the surface,
b) the lower portion of the borehole is en-
larged to form an operating chamber below
the base of the formation,
c) the injection stream has a steam quality of
from about 50% to about 100%, a pressure of
from about 17 kPa to about 44 kPa per meter
of depth from the surface, and a steam in-
jection rate at a water equivalent of
greater than 15 m3/day/well,
d) the plurality of second boreholes varies
from about 2 to about 40,
e) the injection time period of step (d) is at
least 5 days, and
f) the repeated injection/production cycles of
step (h) number at least two.

3. The method of claim 2, wherein
a) the number of second boreholes varies from
about 2 to about 20,
b) the steam injection rate has a water equiva-
lent of from about 80 to about 350 m3/day/
well,

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c) the injection time period can vary from
about 10 to about 100 days, and
d) the repeated injection/production cycles can
number from about 2 to about 25.

4. A method for the in-situ recovery of viscous
materials from a subsurface formation, comprising
a) forming a first borehole to the base of the
subsurface formation to be exploited,
b) extending the borehole below the base of the
formation,
c) drilling a plurality of second boreholes
extending substantially upwardly and radi-
ally outwardly into said formation from the
lower position of the borehole of step (b),
d) injecting steam into said second boreholes,
with the steam having a pressure above the
fracture pressure of the subsurface
formation,
e) maintaining the injection of step (d) for a
time period so as to increase the tempera-
ture of that portion of the formation sur-
rounding said second boreholes and any frac-
ture fissures formed by the injection,
f) releasing the pressure on the system of
boreholes, thus allowing any liberated
material of reduced viscosity to move to the
lower portion of the second boreholes and
thence to the lower portion of the first
borehole,

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g) collecting the liberated material,
h) repeating the injection/production cycle
until the viscous material between at least
some of the second boreholes is made mobile,
i) stopping the steam flow into the second
boreholes,
j) completing selected second boreholes as
producer wells,
k) initiating a flooding procedure, selected
from the procedures consisting of fire
flood, water flood, steam flood, emulsion
flood, and solvent flood, flowing from at
least one injector well to at least one
producing well, and
l) collecting the liberated material.

5. The method of claim 4, wherein
a) the subsurface formation containing viscous
materials is approximately 30 meters or more
below the surface,
b) the lower portion of the borehole is en-
larged to form an operating chamber below
the base of the formation,
c) the injection stream has a steam quality of
from about 50% to about 100%, a pressure of
from about 17 kPa to about 44 kPa per meter
of depth from the surface, and a steam in-
jection rate at a water equivalent of
greater than 15 m3/day/well,

14


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d) the plurality of second boreholes varies
from about 2 to about 40,
e) the injection time period of step (d) is at
least 5 days, and
f) the repeated injection/production cycles of
step (h) number at least two.

6. The method of claim 5, wherein
a) the number of second boreholes varies from
about 2 to about 20,
b) the steam injection rate has a water equiva-
lent of from about 80 to about 350 m3/day/
well,
c) the injection time period can vary from
about 10 to about 100 days, and
d) the repeated injection/production cycles can
number from about 2 to about 25.

7. A method for the in-situ recovery of viscous
materials from a subsurface formation, comprising
a) forming a first borehole to the base of the
subsurface formation to be exploited,
b) extending the borehole below the base of the
formation,
c) drilling a plurality of second boreholes ex-
tending substantially upwardly and radially
outwardly into said formation from the lower
portion of the first borehole of step (b),
d) completing at least one of said second bore-
holes as an injector well, while completing



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the remainder of said second boreholes as
producer wells,
e) injecting steam into said second boreholes
completed as injector wells, with the pres-
sure of the steam above the fracture pres-
sure of the subsurface formation,
f) maintaining the injection of step (e) for a
time period so as to increase the tempera-
ture of that portion of the formation sur-
rounding said second boreholes and any frac-
ture fissures formed by the injection,
g) releasing the pressure on the system of in-
jector boreholes, thus allowing any liber-
ated material of reduced viscosity to move
to the lower portion of the first borehole,
h) repeating the injection/production cycle of
steps (e) - (g) until hydrocarbon between at
least some of said second boreholes is
mobilized,
i) stopping the steam flow to the injector well
and collecting the liberated material,
j) initiating a flood procedure, selected from
the procedures consisting of fire flood,
water flood, steam flood, emulsion flood,
solvent flood, flowing from an injector well
to a producer well, and
k) collecting the liberated material.

8. The method of claim 7, wherein

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a) the subsurface formation containing viscous
materials is approximately 30 meters or more
below the surface,
b) the lower portion of the borehole is en-
larged to form an operating chamber below
the base of the formation,
c) the injection stream has a steam quality of
from about 50% to about 100%, a pressure of
from about 17 kPa to about 44 kPa per meter
of depth from the surface, and a steam in-
jection rate at a water equivalent of
greater than 15 m3/day/well,
d) the plurality of second boreholes varies
from about 2 to about 40,
e) the injection time period of step (d) is at
least 5 days, and
f) the repeated injection/production cycles of
step (h) number at least two.

9. The method of claim 8, wherein
a) the number of second boreholes varies from
about 2 to about 20,
b) the steam injection rate has a water equiva-
lent of from about 80 to about 350 m3/day/
well,
c) the injection time period can vary from
about 10 to about 100 days, and
d) the repeated injection/production cycles can
number from about 2 to about 25.

17

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10. A method for the in-situ recovery of viscous
materials from a subsurface formation, comprising
a) forming a first borehole to the base of the
subsurface formation to be exploited,
b) extending the borehole below the base of the
formation,
c) drilling a plurality of second boreholes
extending substantially upwardly and radi-
ally outwardly into said formation from the
lower portion of the borehole of step (b),
d) injecting steam into said second boreholes,
with the steam having a pressure above the
fracture pressure of the subsurface
formation,
e) maintaining the injection of step (d) for a
time period so as to increase the tempera-
ture of that portion of the formation sur-
rounding said second boreholes and any frac-
ture fissures formed by the injection,
f) releasing the pressure on the system of
second boreholes, thus allowing any liber-
ated material of reduced viscosity to move
to the lower portion of said second bore-
holes and thence to the lower portion of the
first borehole.
g) collecting the liberated material,
h) repeating the injection/production cycle
until the viscous material between at least
some of the second boreholes is mobilized,

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i) stopping the steam flow,
j) completing selected second boreholes as
producer wells,
k) initiating a steam flooding procedure,
l) cyclically varying the steam pressure during
the operation of step (k), and
m) collecting the liberated material.

11. The method of claim 10, wherein
a) the subsurface formation containing viscous
materials is approximately 30 meters or more
below the surface,
b) the lower portion of the borehole is en-
larged to form an operating chamber below
the base of the formation,
c) the injection stream has a steam quality of
from about 50% to about 100%, a pressure of
from about 17 kPa to about 44 kPa per meter
of depth from the surface, and a steam in-
jection rate at a water equivalent of
greater that 15 m3/day/well,
d) the plurality of second boreholes varies
from about 2 to about 40,
e) the injection time period of step (d) is at
least 5 days,
f) the repeated injection/production cycles of
step (h) number at least two, and
g) the steam pressure of step (e) varies from
about atmospheric to the operating pressure.



19

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12. The method of claim 11, wherein
a) the number of second boreholes varies from
about 2 to about 20,
b) the steam injection rate has a water equiva-
lent of from about 80 to about 350 m3/day/
well,
c) the injection time period can vary from
about 10 to about 100 days, and
d) the repeated injection/production cycles can
number from about 2 to about 25.

13. A method for the in-situ recovery of viscous
materials from a subsurface formation, comprising
a) forming a first borehole to the base of the
subsurface formation to be exploited,
b) extending the borehole below the base of
the formation,
c) drilling a plurality of second boreholes
extending substantially upwardly and radi-
ally outwardly into said formation from the
lower portion of the borehole of step (b),
d) completing at least one of said second
boreholes as an injector well, while com-
pleting the remainder of said second bore-
holes as producer wells,
e) injecting steam into said second boreholes
designated injector wells, with the steam
having a pressure above the fracture pres-
sure of the subsurface formation,



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f) maintaining the injection of Step (e) for a
time period so as to increase the tempera-
ture of that portion of the formation
surrounding said second boreholes and any
fracture fissures formed by the injection,
g) releasing the pressure on the boreholes,
thus allowing any liberated material of
reduced viscosity to move to the lower por-
tion of the first borehole,
h) repeating the injection/production cycle
until hydrocarbon between at least some of
said second boreholes is mobilized,
i) initiating a steam flooding procedure, and
j) cyclically varying the steam pressure during
the operation of step (i), and
k) collecting the liberated material.

14. The method of claim 13, wherein
a) the subsurface formation containing viscous
materials is approximately 30 meters or more
below the surface,
b) the lower portion of the borehole is en-
larged to form an operating chamber below
the base of the formation,
c) the injection stream has a steam quality of
from about 50% to about 100%, a pressure of
from about 17 kPa to about 44 kPa per meter
of depth from the surface, and a steam
injection rate at a water equivalent of
greater than 15 m3/day/well,

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d) the plurality of second boreholes varies
from about 2 to about 40,
e) the injection time period of step (d) is at
least 5 days,
f) the repeated injection/production cycles of
step (h) number at least two, and
g) the steam pressure of step (j) varies from
about atmospheric to the operating pressure.

15. The method of claim 14, wherein
a) the number of second boreholes varies from
about 2 to about 20,
b) the steam injection rate has a water equiva-
lent of from about 80 to about 300 m3/day/
well,
c) the injection time period can vary from
about 10 to about 100 days, and
d) the repeated injection/production cycles can
number from about 2 to about 25.

22

Description

Case 5554
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10/12~81


BACKGROUND OF THE INVENTION

This invention relates to a rnethod for the recover~ of
materials such as minerals and viscous hydrocarbons from
subsurface earth formations. In a particular application
S of the invention, the method relates to the in situ recov-
ery of bitumen from tar sands or oil sands.
Various techniques have been considered for recovering
bitumen ~rom tar sand formations that are too deep for sur-
face mining. These techniques typically involve raising
the temperature of the forma-tion to reduce the viscosity of
the bitumen, to assist in the separation of the bit~lmen
from the sand matrix, and to promote movement of the
liberated bitumen. The temperature can be raised by
various means, such as electri.cal heating, fire flooding,
steam flooding, etc. Due to the high expenses and low
recovery rates, these techniques typically have not been
. too successful.
There are also various types of mining techniques fre-
quently used in the prior art to reach and process these
deep tar sands. Some of the techniques used involve
drilling or excavating one or more vertical shafts into the
tar sand formation and then extending lateral horizontal
tunnels from the shaft. U.S. 4,160,481 discusses some of
these techniques.
The inherent and expressed disadvantages of the pri.or
art are overcome with the present invention.
SUM~ARY OF THE INVENTION
There are several embodiments involved in the present
invention, and these generally involve different methods of

;` ''


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entering and then thermally treating the tar sand forma-
tion. All of the embodiments involve a first step of
drilling or excavating a borehole or shaft to the base of
the subsurface formation to be exploited. Typically this
formation is a tar sands or oil sands Formation, but the
` technique can be used in other subsurface formations that
comprise solid and semisolid and viscous materials such as
kerogen, high viscosity hydrocarbon materials such as heavy
oils, inorganic ores, and the like.
The next step involves extension of the borehole or
shaf-t below the base of the formation. This involves
drilling or excavating into the stratum immediately below
the formation to be exploited. This terminal end of the
`~ shaft or borehole, in t`he stratum below the desirecl forma-
tion, is then, optionally ? enlarged to form an operating
; chamber below the base of the desired formation.
~` The next step concerns the drilling of a plurality of
second boreholes extending substantially upwardly and ra-
dially outward into the desired formation from this oper-
ating chamber.
The above-listed steps are common to the first phase
, of the invention. Various embodiments of the invention are
practiced by altering the succeeding steps.
For example, in one embodiment, steam is conducted
down the first borehole or shaft and thence injected into
the plurality of second boreholes drilled from the oper-
ating chamber. Or steam can be generated in the chamber
and then injected into the plurality of boreholes. I~ is a
; feature of this embodiment that the steam used is at a
pressure above the fracture pressure of the formation to be



. ~

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exploited. It is a characteristic of oil sands or similar
hydrocarbon deposits that any flow channels in the forma
tion matrix are effectively plugged with the solid or semi-
solid hydrocarbon material. The rate of injection for
s-team or any other heating medium at subfracture pressures
would be too low to achieve the rate of heat input neces-
sary to recover economically the hydrocarbon. Steam pres-
sures above fracture pressure will permit high rates o~
injection. The injection of this s-team is maintained for a
time period resulting in an increase of the temperature of
that portion of the formation surrounding the boreholes and
the chamber. A "soaking" cycle can follow, for a cliscrete
. time period. When the pressure of the steam on -the system
is released, any liberated material of reduced viscosity
can move, by gravity, and by means of the increased pres-
sure due to the steam injection, to the lower portions of
the second boreholes and thence to the lower portion of the
chamber found in the stratum below the desired formation.
The injection/production cycle is repeated until insuffi-
cient additional hydrocarbon is produced to warrant furthercycles. The recovered viscous material can be moved to the
surface, by means well-known in the art, for further
processing.
The above-mentioned injection/produc-tion cycle is one
of several methods for recovering heavy hydrocarbons from
underground formations. In this invention, two recovery
mechanisms are described and used.
One mechanism involves a stimulation process, such as
by steam. This process involves a single well and is well-




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~.

known in the ar-t as "huff and puff," since steam is in
jected into a reservoir optionally remaining for a finite
soaking period, and then allowed to vent back -through the
entrance. Hydrocarbon production through the entrance is
then noted. Several s-timulation cycles may be needed for
an appreciable outflow of desired material. The injection
well and the production well are the same well, depending
on the time during the stimulation process.
The other mechanism is called a "drive," and at least
two wells are used. Here, for example, steam can be in-
jected into one well, and, after a finite time, production
is noted from a production well.
Pressure cycling, with variations in the steam pres-
sure, can be used for either mechanism.
15In another embodiment, steam, at a pressure above the
fracture pressure of the formation to be exploited, is
injected into the boreholes, as in the above-described
embodiment, continuing the injection/production cycles
until the viscous material between the wells is made
mobile, stopping the steam flow into the injector wells,
completing selected second boreholes as producer wells,
initiating a flooding procedure, exemplified by a fire
flood, water flood, steam flood, emulsion flood, or solvent
flood, flowing from injector wells to production wells, and
collecting the liberated material of reduced viscosity as
before.
In another embodiment, after the second boreholes are
`extended substantially upward and radially outward into the
desired formation from the operating chamber, some of these
second ~oreholes sre completed as in~ector wells, and the

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remainder of -the seconcl boreholes are completed as producer
wells. Then steam, at or above fracturing pressure, is
injected into the second boreholes completed as injector
wells. A number of injection/procluction cycles are carried
out so as to increase the temperature of that portion of
the formation surrounding the boreho:Les. The steam flow
into the boreholes designated as injector wells is then
stopped, and a flooding procedure is initiated, using the
same or a different procedure from the choices noted above,
such that the flooding material flows from injector wells
to producer wells. The liberated material of reduced vis-
cosity is then collected as before.
In a further embodiment of the invention, steam, at a
pressure above fracturing pressure of the desired forma-
tion, is injected into the second boreholes as the begin-
ning of a stimulation phase. The injection/production
cycles of steam stimulation are continued for some time so
as to increase the temperature of the surrounding
formation.
20Selected second boreholes are completed as producer
i wells, and a steam flood is then initiated, with the
; variation that the steam pressure is cylically varied.
Following steps in the procedure are as previousl~
,j.~
decribed.
25In another embodiment, af-ter the second boreholes are
drilled from the chamber into the desired formation, some
of these second boreholes are completed as injec-tor wells
` and the remainder are completed as producer wells. Then
- steam, at a pressure above the fracturing pressure, is
., .
injected into the boreholes comprising the injector wells.



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The previously described injection/production cycles are
carried out, resulting in a temperature increase of the
surrounding formation. A steam flood is then initiated,
with the modification that the steam pressure is cyclically
varied. Liberated hydrocarbon material is then treated as
discussed above.
The embodiments discussed above have one or more of
the advantages discussed below.
A central shaft, with associated radial boreholes, has
- 10 the advantages over wells drilled from the surface of:
- (a) reduced drilling costs~
(b) horizontal wells or boreholes are easier to
drill,
(c) there is less heat loss between the surface and
15the tar sands or oil sands, formation, or reser-
; voir, and
~ (d) the movement of recovered oil from the formation
; to the surface is more efficient than when wells
;.
are drilled from the surface.
20The advantages of continuing the shaft or borehole
into the zone below the formation or reservoir include:
(a) increased safety, since an operating chamber is
~ formed in the zone below the formation,
; (b) wells can be cemented in the zone below the for-
25mation, while there is great difficulty in ce-
- menting wells in an oil sands or tar sands forma-
tion, and
(c) it is easier and safer to complete wells that
have their beginning or terminus in the operating
30chamber below the formation.

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Using a steam pressure greater than the fracturing
pressure of the formation allows injection of the steam
into the formation or reservoir a-t a su-fficient rate to
recover the hydrocarbon product economically. The greater
pressure also allows a higher percentage of the formation
or reservoir to be contacted, and this gives a higher usage
efficiency for the injected steam. This greater pressure
also allows a greater percentage o~ the formation to be
processed.
Cyclical operation involving varying the steam pres-
sure improves the recovery of the product and ofEers an
improved oil/steam ratio. The steam pressure can be varied
from about atmospheric pressure to the operating pressure.
Other advantages of the embodiments of the process
will be noted by those who are skilled in the arts involved
in this process.

DESCRIPTION OF THE DRAWINGS
The ~igure shows a side view of the borehole, the
subsurface formations, the chamber in the formation below
the hydrocarbon-containing formation, and the secondary
boreholes ex-tending from the chamber into the hydrocarbon-
containing formation.

DETAILED DESCRIPTION OF T~IE INVENTION
The described process for the in si-tu recovery of
viscous materials can be used where the desired ~ormation
or reservoir is greater than about 30 meters ~rom the sur-
Eace. For example, the invention is operable where the




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formation or reservoir is from about 90 to about 900 m.
below the surface.
The thickness of the subsurface formation can vary,
such as from about 1 m. to about 300 m, depending on the
geology at that location. Formations thicker than about
5 m. are more economical to work.
In order to reduce the viscosity of, for example, the
tar sands or oil sands found in the formation, an operating
temperature of about 40C or higher is desirable. The tem-
perature of satura-ted steam at the injection pressure in
the formation will give a gradient of operating tempera-
tures, being hi~hest near the injection nozzle and becoming
lower as the distance from the injection nozzle increases.
The q~lality of the steam used for injection can vary
from about 50% to about 100%. The injec-tion pressure used
should be of the order of about 17 kPa/m or more, prefer-
ably from about 22 to about 44 kPa per meter of depth.
The steam injection rate should be about the water equiva-
lent of 15 m3/day/well or more, preferably from about 80 to
about 350 m3/day/well.
The number of vertical shafts penetrating the over-
burden, and the material ~mderlying the formation will
depend on the size of the deposit and the desired produc-
' tion rate. The minimum number is 1, while a preferred or
~- 25 working number can vary between about ~ and about 25.
; The drawing illustrates a simplified cross-section
., :
`~ view of an in SitU operation. A shaft, or first bore-
hole 2, is sunk through overburden 1 into the desired
'; formation 3. The borehole is continued into the underlying
stratum 4 below the desired ~ormation 3, and chamber 5 is

,'. 9
.,
.


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an optional structure at the base of the first borehole 2.
From chamber 5, second boreholes 6 are drilled upwardly and
radially outwardly, to penetrate formation 3. ~asing 7 is
used to reduce the probability of collapse of borehole 6
while in stratum 4. One embodiment of production tubing
(borehole 6 completed as a producing well) is shown as 8.
Some known method of moving material libera-ted from the
borehole to the surface, such as a pump~ is not shown.
The stimulation in~ection time should be 5 days or
more, such as from about 10 to about 100 days. The stimu-
lation cycles are l or more, such as from about 5 to
about 25.
The number of second borehol.es extending upwardly and
radially outwardly from -the lower formation into the
hydrocarbon-bearing formation can vary from about 2 to
about 40~ preferably from about 2 to about 20. The radial
length of these second boreholes can vary from a few
. meters, such as about 10, to a length that will allow
.; connection with another, distant well, after the tempera-
ture of the intervening formation has been raised to allow
movement of the desired material, such as a viscous hydro-
carbon. This latter distance may vary from about 50 m. to
about 600 m.



'~