Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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F-2527 1-
METHOD FOR RECOVERING OIL BY
IN SITU COMBUSTION USING OXYGEN
This invention concerns an o~ygen driven in situ combustion
oil recovery method which permits efficient recovery of oil from a
subterranean, perrneable, oil-containing formation containing about 20
API gravity oil with a continuously underlying water zone.
A variety of supplemental recovery techniques have been
employed in order to increase the recovery of oil from subterranean
viscous oil-containing formations. These techniques include thermal
recovery methods, waterflooding and miscible flooding.
of the aforementioned recovery ~ethods, in-situ combustion
appears to be the most promising method of economically recovering
large amounts of viscous hydrocarbon deposits with currently available
technology. The attractiveness of the in-situ combustion method
arises primarily from the fact that it requires relatively little
energy necessary for sustaining combustion of the hydrocarbon
deposits. In contradistinction, other in-situ techniques, such as
electrical resistance heating and steam injection require considerable
amounts of energy, e.g., to produce tne steam at the surface before it
is injected into the viscous oil-containing formation.
Conventional in-situ combustion involves drilling of at least
two substantially vertical wells into the formation, the wells being
separated by a hori~ontal distance within the formation. ~ne of tne
wells is designated an injection well, and the other a production
well. The recovery of oil is accomplished oy raising the temperature
of the in-place oil adjacent the injection well to ignition
temperature by some suitable means, e.g., with some type of a
conventional down hole heater/burner apparatus, or by steam injection
and then supporting combustion by injecting an oxygen-containing gas
such as air, oxygen enriched air, oxygen mixed with an inert gas, or
substantially pure oxygen. Thereaf~er, the injection of the
oxygen-containing gas is continued so as to maintain the high
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temperature combustion front which is formed, and to drive the front
through the formation toward the production well. As the combustion
front moves through the formation, it displaces ahead of it the
in-place oil reduced in viscosity as well as other formation fluids
such as water and also combustion gas produced during the combustion
process. These fluids are recovered from the formation via the
production well.
In these processes, the gaseous combustion products and light
hydrocarbons are considerably lighter than the oil and water present
in the reservoir and thus, because of gravity segregation, tend to
rise to the top of the reservoir when vertical communication exists.
Conse~uently, these products channel through the top of the formation
to the producing well overriding a major portion of the reservoir and
contacting only a small fraction of the reservoir oil. This behavior
results in inefficient oil recovery and low vertical sweep efficiency.
The present invention provides a method for conducting an in
situ combustion oil recovery operation using essentially pure oxygen
in a subterranean, permeable, oil-containing formation containing
about 20 API gravity oil with a continuous underlying water zone
wherein vertical sweep efficiency is increased tnereby significantly
enhancing oil recovery.
This invention relates to a method for the recovery of oil
from a subterranean, permeable, oil-containing formation containing
about 20 API gravity oil overlying and in contact with a
water-saturated formation, said oil-containing formation being
penetrated by at least one injection well and at least one
spaced-apart production well, comprising establishing fluid
communication between the injection well and only the lower 15 percent
of the vertical thickness of the oil-containing formation,
establishing fluid communication between tne production well ana only
the upper 70 percent of the vertical thickness of the oil-containing
formation, injecting essentially pure oxygen into the oil-containing
formation via the injection well to initiate an in situ combustion
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front in the bottom of the oil-containing formation and continuing to
inject essentially pure oxygen into the bottom of the oil-containing
formation to advance the combustion front through the formation toward
the production well and recovering fluid including oil from the upper
7û percent of the oil-containing formation via the production well.
According to a preferred embodiment of the invention, an
improvement in an oxygen-driven in situ combustion method for the
recovery of oil from a subterranean, permeable, oil-containing
formation containing a~out 20 API gravity oil overlying and in
contact with a water-saturated formation, said oil-containing
formation being penetrated by at least one injection well and at least
one spaced-apart production well, comprises:
(a) establishing fluid communication between the
injection well and only the lower 15 percent of the
vertical thickness of the oil-containing formation;
(b) establishing fluid communication between the
production well and only the upper 70 percent of
the vertical thickness of the oil-containing
formation;
(c) injecting essentially pure oxygen into the
oil-containing formation via the injection well to
initiate an in situ combustion front in the bottom
of the oil-containing formation and the top of the
water-saturated zone; and
(d) continuing to inject essentially pure oxygen into
the bottom of the oil-containinq zone and the top
of the water-saturated zone to advance the
combustion front through the formation toward the
~roduction well and recovering fluid including oil
from the upper 70 percent of tne oil-containing
formation via tne production well.
A further preferred embodiment of the invention comprises an
improved oxygen driven in situ combustion method for recovering oil
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from a subterranean, perrneable, oil-containing formation containing
about 20 API oil wherein said forrnation is overlying and in contact
with a water-saturated forrnation; and said formation is penetrated by
at least one injection well in fluid communication with only the lower
15 percent of the oil-containing formation and at least one
spaced-apart production well is in fluid commur,ication with only the
upper 70 percent of the oil-containing forrnation, and the improvement
comprises the steps:
(a) injecting essentially pure oxygen into only the
lr~wer 15 pe~cent of the oil-containing fr,nTation
via said injection well to establish an in situ
combustion front in said oil-containing formation;
and
(b) continuing injection of said oxygen to support the
in situ connbustion front and producing oil frorn
only the upper 70 percent of the oil-containing
forrnation via said production well.
The invention is better understood by referring to the
drawings appended hereto. In the drawings,
Fiqure 1 illustrates a subterranean, oil-containing ~ormation
containinq about 20 API oil overlying and in contact with a water
zone to which the process of our invention is being applied and
showing the rnethod of cornpleting the wells. Also, in the drawings,
Figures 2 and 3 show grid systems for simulation runs with
the location and cornpletion of an oxygen injection well, production
wells, and water injection wells.
Referring to Figure 1 of the appended drawings, there is
shown a subterranean, Permeable~ oil-containing formation 10
containing an oil which has an API gravity of about 20 API overlying
and in contact with a water saturated zone 12, which is essentially
continuous along the bottom portion of the oil-containing forrnation 10
to be exPloited by rneans of the subject process. The oil-containing
formation 10 is penetrated by at least one injection well 14 and at
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least one spaced-apart production well 16. Injection well 14 is
perforated or other fluid flow communication is established between
the well as shown in Figure 1 with only the lower 15% of the vertical
thickness of the oil-containing formation. Production well 16 is
completed in fluid communication with only the upper 70% of the
vertical thickness of tne oil-containing formation lû. While recovery
of the type contemplated by the present invention may be carried out
by employing only two wells, it is to be understood that the invention
is not limited to any particular number of wells. The invention may
be practiced using a variety of well patterns as is well known in the
art of the oil recovery, such as an inverted five spot pattern in
which an injection well is surrounded with four production wells, or
in a line drive arrangement in wnich a series of aligned injection
wells and a series of aligned production wells are utilized. Any
number of wells which ~ay be arranged according to any pattern ~ay be
applied in using the present method as described and illustrated in
U.S. Patent No. 3,927,716 to Burdyn et al. Either naturally occurring
or artificially induced fluid communication should exist between the
injection well 14 and the production well 16. fluid communication can
be induced by techniques such as cyclic steam or solvent stimulation
or fracturing using procedures well known in the art. Well-to-well
fluid communication is essential to the proper functioning of tne
process according to the invention.
An in situ combustion front is established only in the lower
portion of the oil-containing formation 10 overlying the
water-saturated zone 12 ~y injecting essentially pure oxygen into the
injection well 14 until a corresponding increase in temperature
indicates that ignition has taken place and a combustion front is
formed. In situ combustion can be initiated in the lower portion of
the oil-containing formation 10 by methods well known in the art
through the use of electric downhole heaters, downhole gas burners,
chemical injectors, or spontaneous ignition using a mixture of oxygen
and steam.
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Thereafter, injection of oxygen into the lower portion of the
formation 10 via injection well 14 is continued to sustain the
combustion reaction and advance the combustion front through the
formation toward the production well 16 and fluid including oil is
recovered from only the upper 70% of the formation via the production
well 16. The oxygen injection rate will vary according to
characteristics of individual formations such as thickness, depth and
oil saturation. The heat generated by the in situ combustion front
reduces the viscosity of the in place oil and the advancing combustion
front effectively displaces ahead of it the mobilized oil which is
recovered from the upper portion of the formation 10 via the
production well 16. The recovery of fluid including oil is continued
until the combustion front has progressed through the formation 10 to
the production well 16 which is determined once the temperature at the
production well begins to rise. The present in situ combustion
operation using essentially pure oxygen and a specific injection and
production well completion applied to a permeable formation containing
about 20 API oil overlying and in contact with a water zone results
in improved sweep efficiency thereby significantly enhancing oil
recovery.
!Jtilizing a computational model and computer program will
demonstrate the enhanced oil recovery achieved from the application of
the process according to the invention.
A three-phase black oil simulator was used to simulate an
oil-containing formation overlying and in contact with a water zone
wherein the oil-containing formation contains about 1730 barrels of
total oil in place at a viscosity of 90 cp and an API gravity of 20.
Table 1 below lists the reservoir properties used in the computational
model.
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TABLE 1
Rese voir Data
Net pay, feet 35
Porosity, % 31
Permeability, md 1000, 2500 and snoo
Reservoir pressure, psi 1200
Depth (subsurface), feet 2660
Oil viscosity, cp 90
Oil saturation, %, P.V. 45%, 15%, 2%
Reservoir temperature, F 125
Figure 2 of the drawings shows a vertical cross section of
the model formation used and location of five wells, an oxygen
injection well 1 in fluid communication with only the upper 14% of the
formation as indicated by the dashed lines, two separate production
wells 2 and 3 in fluid communication with only the upper 71% of the
formation as indicated by the dashed lines, well 4 in Block 1 to model
the effect of non-closed patterns and a water injection well 5 which
maintains reservoir pressure to simulate an aquifer. Figure 3
illustrates the sa~e ~odel as shown in Figure 2 except that injection
well 1 is completed to be in fluid communication with only tne lower
14% of the oil-containing formation.
The model for~ation shown in Figures 2 and 3 is at a 2 dip
an~le and was used with a reactangular mode consisting of 19 blocks in
the X or horizontal direction and 8 blocks in the Z or vertical
direction. The injection well 1 was operated with constant injection
rate. The production wells were operated with a flowing bottom hole
pressure of 1100 psi. The vertical thickness of each layer from top
to bottom is 3.5 feet and the bottom layer which represents an
underlying water zone is 10.5 feet in thickness. The cross-sectional
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thickness, ~Y is 20 feet and the width9 ~X, is 39.3 feet for grids 1
and 2, 26 feet for grids 3 to 14, 118 feet for grids 15 and 16 and
39.3 feet for grids 17 to 19. The hatched blocks in Figures 2 and 3
depict burned zones having zero oil saturation at oxygen breakthrough
and 350 and 40nF temperature isotherms are also shown in these
figures at oxygen breakthrough.
Two runs ~ere made using the well completions shown in
Figures 2 and 3 and a third run with the injection well 1 completed in
the lower 10% of the vertical thickness of the formation a distance of
3.5 feet above the water zone. The results of the three runs are
summarized in Table 2 below.
TABLE 2
Injection well
Complet_on Injection RateOil Recovery B.T.T.,_
X-grid Z-grid ~SCF/day % days
14 1 30 12.5 180
14 6 30 21.0 300
14 7 30 28.7 33a
The results clearly show that maximum total oil recovery of
28.7% is achieved when the injection well is completed in the lower
portion of the oil-containing formation compared to 12.5% and 21.0%
for the other cases. The increased oil recovery is a result of a more
uniform vertical sweep and heating of the formation.
