Note: Descriptions are shown in the official language in which they were submitted.
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VISCOUS OIL RECOVERY METHOD
This invention relates to a -thermal process ~or recoverin0 oil
From a subterranean, viscous oil-containing formation. More
particularly, this invention relates to a thermal method o~ recovering
oil ~rom a viscous oil-containing formation, especially a highly viscous
tar sand deposit, employing an injection system for injecting a thermal
fluid into the bottom portion of the formation and a sequence of
manipulative steps with steam and hot water to obtain maximum heat
utilization and oil recovery from a spaced-apart production well
completed in the upper portion of the formation.
Increasing worldwide demand for petroleum products, combined
with continuously increasing prices for petroleum and products recovered
therefrom, has prompted a renewed interest in the sources of
hydrocarbons which are less accessible than crude oil of the Middle East
and other countries. One of the largest deposits of such sources of
hydrocarbons comprises tar sands and oil shale deposits found in
Alberta, Canada, and in the Midwest and Western states of the United
States. While the estimated deposits of hydrocarbons contained in tar
sands are enormous (e~g., the estimated total of the deposits in
Alberta, Canada is 250 billion barrels of synthetlc crude equivalent),
only a small proportion of such deposits can be recovered by currently
available mining technologies, such as, by strip mining. For example,
in lY74, it was estimated that not more than about lO~o of the then
estimated 250 billion barrels of synthetic crude equivalent of deposits
in Alberta, Canada was recoverable by the then available rnining
technologies, SYNTHETIC FUELS, March 1974, pages 3-1 through 3 14). The
balance must be recovered by various in-situ techniques such as
electrical resistance heating, steam injection and in-situ forward and
reverse combustion.
Of the aforementioned ir.-situ recovery methods9 steam ~looding
has been a widely-applied method for heavy oil recovery. Problems
arise, however, when one attempts to apply the process to heavy oil
reservoirs with very low transmissibility such as tar sand deposits. In
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such cases, because of the unfavorable mobility ratio, steam channelliny
and gravity override often result in early steam breakthrough and leave
a large portion of the reservoir unswept. The key ko a successful stearn
flooding lies in striking a good balance between the rate of
displacement and the rate of heat transfer which lowers the oil
viscosity to a more favorable mobility ratio.
Copending Canadian application Serial No. 431,321 discloses a
thermal method ~or the recovery of oil from a subterranean, viscous
oil-containing ~ormation, wherein steam in an amount ranging from 0.~ to
0.5 pore volume at an injection rate within the range of 4.0 to 7.0
bbl/day/ac.-ft. is injected into the formation via an injection well
completed in the lower half of the formation and fluids including oil
are recovered via a spaced apart production well completed in the upper
half of the formation. The injection well is then shut-in for a
variable time and thereafter a predetermined amount of hot water or low
quality steam is injected into the formation via the injection well in
an amount ranging ~rom 0.0~ to 0.10 pore volume and at an injection rate
of 1 to 2.0 bbl/day/ac.-ft. The method is applied to viscous
oil-containing formation in which either naturally occurring or induced
communication exists bet~een the injection well and the production well
in the bottom zone of the formation. The injection well and production
well are spaced apart 400 to 750 feet.
Copendin~ Canadian application Serial No. 419,671 discloses a
thermal method for the recovery of oil from a subterranean, viscous
oil-containing formation, wherein a predetermined amount of steam in an
amount not greater than 1.0 pore volume is injected into the formation
via an injection well and oil is produced from the formation via a
production well. The injection well is then shut-in for a variable time
to allow the injected steam to dissipate its heat throughout the
formation and reduce oil viscosity while continuing production o~ oil.
A predetermined amount of hot water or low quality steam in an amount
not greater than 1.0 pore volume i5 injected into the formation with
continued production but avoiding steam breakthrough. Thereafter,
production is continued until there is an unfavorable amount of water or
steam in the fluids recovered.
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Accordingly, this invention provides an improved thermal system
for effectively recoverlng oil ~rom subterranean formations such as tar
sand deposits utilizing an injection well and production well completion
combined with manipulative steam flooding. The injection well may be
characterized by terminating in a cavity in the formation, terminating
horizontally or extending through and being in fluid communication with
a horizontal fracture in the lower part of the formation.
A subterranean, low transmissibility, viscous oil-containing
formation is penetrated by at least one injection well and at least one
spaced-apart production well. The production well is completed so that
it is in fluid communication with the upper twu-thirds or less of the
vertical thickness of the formationl
In the embodiment wherein the injection well terminates in a
cavity within the formation, said cavity is not to be greater than 0.10
pore volume. Alternately, the lower portion of the formation may be
fractured to form a hnrizontal fracture extending radially ~rom and in
fluid communication with the injection well. In a ~urther embodiment,
the injection well may extend horizontally through the formation for a
distance of from about one-third to one-half of the distance between the
vertical sections of the injection and production wells.
A slug of steam in an amount within the range of 0.35 to 0.45
pore and at a rate of from 4.5 to 6.5 bbl/day/ac.ft is injected into the
cavity in the lower portion formation via the injection well and
recovering fluids including oil from the formation via said production
well. Simultaneously during injection of the steam into the injection
well and fluids are being produced from the production well, a solvent
or steam injection-production process may be applied at the production
well. This process is ~pplied si~ultaneously with the steam drive
process in a series of repetitious cycles throughout the entire time
that the steam drive sequence is being applied and particularly in the
early stages to enhance production. After the first slug of steam has
been injected into the for~ation, the injection well is shut-in for a
predetermined period of time and the recovery of ~luids includLng oil
is continued from the production well without steam breakthrough.
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Thereafter, a predetermined amount, preferably 0.03 to 0.10 pore volume,
o~ hot water or low quality steam is injected into the formation via the
injection well and fluids including oil are recovered from the ~ormakion
via the produotion well. The hot water or low quality steam is injected
at a rate of from 1 to 1.5 bbl/day/ac--ft. The slug of hot water or
low quality steam may be injected for a plurality of cycles.
Thereafter, production of fluids including oil is continued from the
production well until the recovered fluids contain an unfavorable amount
of steam or water.
Figure 1 illustrates a subterranean oil-containing formation
being subjected to the improved steam flooding techniques in the present
invention, penetrated by an injection well in fluid communication with a
cavity formed in the bottom portion 3f the formation and a spaced-apart
production well in fluid oommunicatinn with the upper portion of the
formation.
Figure 2 illustrates Applicant's oil recovery method wherein
the formatiGn is penetrated by an injection well having a horizontal
fracture extending radially thrnugh the formation therefrom.
, Figure 3 illustrates yet another embodiment of this
application wherein the iniection well is deviated in the lower portion
of the formation.
Referring to Figure 1, a relatively thick, subterranean, low
transmissibility, viscous oil-containing formatinn 10 is penetrated by
at least one injection well 12 and at le~st one spaced-apart production
well 14. The injection well 12 extends from the earth's surface into
the lower portion of the formation 10 and is in fluid co~munication with
a cavity 16 ~ormed by a borehole mining technique such as the on~
described in and by A.B. Fly, "Hydro-Blast Mining Shoots Ahead", Mining
~ngineering, pp. 56-58, March (1969). In this method of forming cavity
16~ a bore-hole mining tool is lowered through the injection well 12
into the bottom part of the formation 10. The tool is rotated and
sidewall fit streams are sent out at a high speed to cut the formation
and wash the cuttings down to the rock pits. This creates a void space
or cavity 16 in the bottom part o~ the formation 10 which preferably
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does not extend more than about 1/3 to 1/2 of the distance between the
injection well 12 and production well 14. Also, khe vertical thickness
of the cavity 16 is not more than 1/5th the vertical thickness of the
formation 10. The latter limitations on the size of the cavity 16
creates a cavity no larger than 0.1 pore volume of the reservoir
underneath the well pat'cern. The production well 14 is per~orated to
establish fluid communication with the upper portion of the formation,
not exceeding two-thirds the vertical thickness of the formation.
Referring to Figure 2, the injection well 112 extends from the
earth's surfaoe into the lower portion of the formation 110 and is
provided with a notch 116 for injection of a fracturing fluid to form a
horizontal fracture 118 in the lower portion of the formation. The
injection well 112 is first notched by rotating a hydraulic cutting tool
to form notch 116. The formation may be hydraulically fractured tn form
a radially extending horizontal fracture 118 around the injection well
by injection of steam at a very high rate. This method is disclosed in
U.S. Patent No. 4,265,310.
Figure 3 depicts a further embodimerlt wherein formation 210
is penetrated by at least one devia~ed injeotion well 212 and at least
one spaced-apart production well 214. The injection well 212 extends
downwardly ~rom the earth's surface and into the oil containing
formation 210 having a substantially vertical section 216 and a
substantially horizontal section 218 extending a predetermined distance
through the formation near the bottom thereof. The horiæontal section
218 is provided with perforations 220 to establish fluid communication
with the lower portion of the formation 210. The horizontal section
extends a distance of about one-third to one-half the distance between
the vertical section 216 of the injection well 212 and the production
well 2140 The horizontal section 21B of the injection well should be
completed with a slot liner (not shown) or other sand-control means to
prevent blockage of fluid flow such as disclosed in U~S. Patent No.
~,116,275. The production well 214is perforated to establish fluid
communication ~ith the upper portion of the formation, not exceeding
two~thirds of the vertical thickness of the formation.
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Once the wells are established, a slug of steam ranging from
0.35 to 0.45 pore volume and preferably 0.37 pore volume is injected
into the formation via the injection well and flu.ids including oil are
recovered from the formation via production well. The steam is injected
at a predetermined rate ranging from 4.5 to 6.5 bbl/day/ac.ft and
preferably 5.0 bbl/day/ac.ft. Because of the low transmissibility of
the formation, initially the total fluid production rate will be much
less khan the injection rate and formation pressure will increase.
Ouring the initial portion o~ the above-described steam
injection, the production well may be steam or solvent stimulated by a
steam/solvent injection-production sequence or push-pull process. This
sequence comprises injecting a predetermined amount of steam or solvent
into the formation via the production well and then returning the well
to production. The above sequence of steam or solvent injection
followed by ~luid production may be repeated for a plurality of cycles.
Suitable solvents include C2 to C10 hydrocarbons and their mixtures, as well
as commercial solvents such as kerosene, naph~la and natural gasoline.
After the s}ug of steam has been injected into the ~ormation
via injection well, the injection well is shut-in ~or a predetermined
period of time and production is continued. This soak-period allows
heat to dissipate into the formation further thereby reducing the
viscosity of the oil. The high completion, upper two-thirds or less of
the formation allows a vertical growth of the steam zone originating
from the low viscous finger as pressure decreases and steam rises in the
formationO As the heated zone grows, the rate of production increases
and the formation pressure is drawn down.
After the injection well has been shut-in for a predetermined
period of time and production continued but without steam breakthrough7
a second slug of a heated fluid, preferably hot water or low quality
steam, is ;njected into the formation via the injection well and
production is continued until there is an unfavorable amount of steam or
water in the fluids recovered fro~ the formation via the production
well. The quality of the steam injected is not greater than 20%. The
amount of heated fluid injected is from 0.03 to 0~10 pore volume at an
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injection rate of 1 to 1.5 bbl/day/ac.ft. During injection of the
heated fluid, the formation will be pressurized and additional mobilized
oil will be displaced through the formation for recovery via the
production well. It is preferred during this step to inject hot water
as the thermal fluid because, unlike steam, it will not migrate upwardly
through the formation but is able to appropriate heat: from the steam
already present in the formation and cause it to condense thereby
deterring steam channeling. This extends the production time by
delaying steam breakthrough at the production well. Additional slugs of
hot water or low quality steam may be injected into the formation via
injection well for a plurality of cycles.
By the term ~Ipore volume" as used herein, is meant that volume
of the portion of the formation underlying the well pattern employed as
described in greater detail in U.S. Patent No. 3,927,716.
While the invention has been described in terms of a single
injection well and a single spaced apart production well, the method
according to the invention may be practiced using a variety of well
patterns. Any other number of wells, which may be arranged according to
any patterns, may be applied in using the present method as illustrated
in U.S~ Patent No. 3~927,716. However, if the wells are too far apart,
formation communication is usually limited.
