U.S. patent number 3,905,422 [Application Number 05/508,385] was granted by the patent office on 1975-09-16 for method for recovering viscous petroleum.
This patent grant is currently assigned to Texaco Inc.. Invention is credited to Charles D. Woodward.
United States Patent |
3,905,422 |
Woodward |
September 16, 1975 |
Method for recovering viscous petroleum
Abstract
The efficiency of an oil recovery process, being applied to a
subterranean, viscous petroleum containing formation such as a tar
sand deposit involving the injection of a thermal recovery fluid
such as steam, heated air or hot water into an injection well to
mobilize and displace petroleum toward a production well is
improved by drilling a series of secondary injection wells or
pressurization wells around the production wells. Unheated air is
injected into the secondary injection wells at a pressure from
about 10% to about 90% and preferably around 50% of the pressure at
which the thermal recovery fluid is being injected into the central
injection wells. A pressure gradient is maintained around the
production wells which confines the mobilized petroleum and the
thermal recovery fluid to the intended pattern. A low temperature
oxidation reaction also occurs as a consequence of the unheated air
injection which pretreats petroleum in the formation between the
air pressurization wells and the production wells so that the next
phase of oil recovery is improved.
Inventors: |
Woodward; Charles D. (Houston,
TX) |
Assignee: |
Texaco Inc. (New York,
NY)
|
Family
ID: |
24022550 |
Appl.
No.: |
05/508,385 |
Filed: |
September 23, 1974 |
Current U.S.
Class: |
166/245;
166/272.3; 166/256 |
Current CPC
Class: |
E21B
43/30 (20130101); E21B 43/24 (20130101); E21B
43/243 (20130101) |
Current International
Class: |
E21B
43/00 (20060101); E21B 43/243 (20060101); E21B
43/24 (20060101); E21B 43/30 (20060101); E21B
43/16 (20060101); E21B 043/24 () |
Field of
Search: |
;166/256,272,259,245,268 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Novosad; Stephen J.
Attorney, Agent or Firm: Whaley; T. H. Ries; C. G. Park;
Jack H.
Claims
I claim:
1. In a method of recovering petroleum from a subterranean
petroleum containing formation penetrated by at least one injection
well and by at least one production well, of the type wherein
thermal recovery fluid is introduced into the injection well and
petroleum is recovered from the remotely located production well,
wherein the improvement for increasing the capture efficiency of
the oil recovery operation and for pretreating a portion of the
formation for the next phase of the oil recovery method
comprises:
a. completing at least one gas pressurization well in the formation
on the opposite side of the production well from the thermal
recovery fluid injection well,
b. introducing a gaseous material into the pressurization well at a
pressure less than the pressure at which the thermal recovery fluid
is introduced into the injection well for the purpose of
pretreating the formation petroleum and creating a pressure
gradient around the additional well which serves to confine the
injected fluid in mobilized petroleum, and
c. recovering petroleum from the production well.
2. A method as recited in claim 1 wherein the fluid injection into
the pressurization well is air.
3. A method as recited in claim 1 wherein the temperature of the
gaseous material is below 400.degree.F.
4. A method as recited in claim 1 wherein the temperature of the
gaseous material is below 200.degree.F.
5. A method as recited in claim 1 wherein the pressure at which the
gaseous material is injected into the pressurization well is from
about 10% to about 90% of the pressure at which the thermal
recovery fluid is injected into the injection well.
6. A method as recited in claim 1 wherein the thermal recovery
fluid is steam.
7. A method as recited in claim 1 wherein the thermal recovery
fluid is heated air.
8. A method as recited in claim 1 wherein the thermal recovery
fluid is a mixture of air and steam.
9. A method as recited in claim 1 wherein a plurality of production
wells are drilled around at least one centrally located injection
well, and a plurality of pressurization wells are drilled around
the pattern defined by the production wells.
10. A method as recited in claim 9 wherein the pressurization wells
are later converted to production wells after the oil mobilizing
fluid has broken through into the production wells.
11. A method of recovering bitumen from a tar sand deposit
comprising
a. penetrating the tar sand deposit with at least one injection
well;
b. penetrating the tar sand deposit with a plurality of production
wells equally spaced around the injection well;
c. penetrating the formation with a plurality of air pressurization
wells located at a greater distance from the injection wells than
the production wells;
d. introducing a thermal recovery fluid into the injection
well;
e. recovering petroleum from the production wells; and
f. injecting air into the outer pressurization wells at a pressure
between about 10% and about 90% of the pressure at which the
thermal recovery fluid is injected into the central injection well
and at a temperature below 400.degree.F.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application is related to commonly owned application Ser. No.
493,286, filed July 31, 1974.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to an oil recovery process and more
particularly to a supplemental oil recovery process for use in
recovering viscous petroleum from subterranean formations including
tar sand deposits. Still more particularly, this invention pertains
to a method for pretreating a section of the formation immediately
surrounding a pattern being subjected to a supplemental oil
recovery process in order to confine the recovery fluid in the
pattern and also to pretreat the formation in preparation for the
second phase of the oil recovery process.
2. Description of the Prior Art
When oil is discovered in subterranean reservoirs, certain
conditions must be present in order to be able to recover the oil
from the formation. It is necessary that the oil viscosity be
sufficiently low that it is mobile, e.g. that it will flow if
sufficient force is applied to it. Moreover, the formation must
have adequate permeability or flow channels so that fluids may move
from one point in the formation to another. Finally, some drive
force must exist naturally or be supplied to the formation in order
to move the formation petroleum to a production well where it may
be pumped to the surface of the earth. When natural energy such as
solution gas, gas cap or bottom water drive is present, oil may
flow spontaneously without the application of any additional drive
force and this phase of oil recovery is referred to as primary
recovery. When the oil viscosity is sufficiently low and there
exists satisfactory formation permeability but insufficient natural
energy exists to cause it to flow to the surface of the earth,
water drive or water injection may be utilized to drive or displace
oil toward a production well. This is commonly referred to as
secondary recovery.
There are many formations throughout the world which contain
petroleum whose viscosity is so great that the petroleum will not
move even if sufficient natural or artificial drive force is
applied to it, even though the formation permeability is adequate.
This petroleuum is commonly referred to as viscous oil or heavy oil
or low API gravity oil. For the purpose of this application,
viscous petroleum or heavy oil is defined as petroleum whose API
gravity is less than about 12.degree. API. The most extreme example
of viscous petroleum containing formations are the so called
bitumen sand or tar sand deposit such as those located in the
western United States and in Alberta, Canada. The bituminous
petroleum contained in tar sand deposits is essentially immobile at
formation temperature, and so substantial supplemental treatment
must be applied to bituminous petroleum in order to render it
sufficiently mobile that it will move to a production well so that
it may be recovered to the surface of the earth.
One of the most popular methods for recovering viscous petroleum
such as bituminous petroleum from subterranean formations such as
tar sand deposits which are too deep to permit strip mining
thereof, is steam flooding. Steam is injected into one well and
travels to a remotely located well from which it is recovered to
the surface of the earth. The principal effect of steam injection
is the increase in petroleum temperature which reduces the
viscosity of the petroleum. Although the viscosity of bituminous
petroleum in a tar sand deposit is in the range of millions of
centipoise at normal formation temperatures, the
viscosity-temperature relationship is exceedingly sharp, and the
viscosity of the bituminous petroleum is reduced to only a few
centipoise at around 300.degree.F.
Numerous problems prevent effective utilization of steam injection
in tar sand deposits. Because of the fact that steam is principally
in the vapor phase when it is injected into the formation, the
steam does not displace petroleum in a piston-like fashion, and
much loss of the injected steam to the surrounding formation beyond
the confines of the pattern being utilized in the supplemental oil
recovery process occurs, with the attendant loss of thermal
efficiency. Moreover, because of the extremely high viscosity of
bituminous petroleum, the viscosity reduction resulting from
petroleum being contacted with steam is frequently not sufficient
to mobilize the highly viscous petroleum, and some form of
pretreatment must be utilized.
Even though the petroleum viscosity is reduced as a consequence of
being heated with steam, bituminous petroleum is quite prone to
form high viscosity water-in-oil emulsions, which are viscous and
difficult to displace through the formation.
In view of the foregoing discussion, it is apparent that there is a
substantial unfulfilled need for a method of conducting a steam
flooding operation in viscous petroleum containing formation so as
to minimize the loss of injected steam to the surrounding formation
beyond the confines of the pattern of the wells being utilized in
the supplemental oil recovery process, and further to pretreat the
formation so as to improve the efficiency of the steam flooding
operation and to minimize the formation of water-in-oil
emulsions.
SUMMARY OF THE INVENTION
Briefly, my invention comprises a process for recovering viscous
petroleum from the subterranean formation wherein at least one
injection well is drilled in the formation and a plurality of
production wells are arranged symetrically around the production
well, and a thermal recovery fluid such as steam, heated air, a
mixture of steam and air or hot water is injected into the
injection well to heat the formation within the pattern defined by
the production wells so as to mobilize the viscous petroleum
contained in the formation within the pattern. A plurality of air
pressurization wells are drilled around the production wells in a
generally symetrical fashion, and air is injected into the air
pressurization wells at a pressure from about 10% to about 90% of
the pressure at which the thermal recovery fluid is being
introduced into the injection well. As a consequence of the air
pressurization step, a pressure gradient is formed around the
pattern which serves to confine the thermal recovery fluid, thereby
improving the capture efficiency of and thermal efficiency of the
thermal recovery operation. Air injection also pre-exposes the
subterranean formation to air at a low temperature, thereby
pretreating the formation so as to render it more responsive to oil
recovery by thermal means such as steam, in situ combustion, or low
temperature oxidation recovery. After the main thermal recovery
fluid has broken through at the production wells in the pattern,
the production wells are converted to thermal recovery fluid
injection wells and the air pressurization wells are converted to
new production wells, and the thermal recovery operation is
extended outward to the area previously pretreated by air
pressurization.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 illustrates in plan view a four well pattern for practicing
my invention comprising one thermal recovery fluid injection well,
one production well, and two air pressurization wells.
FIG. 2 depicts in plan view a field being exploited by means of a
thermal drive in which a central thermal recovery fluid injection
well is surrounded by four production wells, and located around the
four production wells are eight air pressurization wells for use in
practicing the process of my invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Briefly, my invention involves the drilling of one or more wells in
an area of the formation remote from a group of injection and
production wells being used to recover oil by a thermal recovery
means such as steam flooding, in situ combustion, air-steam
controlled combustion, or hot water flooding. The additional wells
are drilled outside of the area in which recovery is expected to be
effected during the course of the first phase of the supplemental
oil recovery operation.
In its simplest embodiment, as little as one injection well and one
production well may be involved in a supplemental recovery
operation, and one or more additional wells may be drilled outside
of the anticipated swept area between the injection well and
production well for the purpose of injecting unheated air into the
formation to create the desired pressure gradients. As can be seen
from FIG. 1, the wells will be located on the opposite side of the
production well from the injection well, so as to form an
encircling pressure gradient when unheated air is injected into the
additional air pressurization wells. After the thermal recovery
fluid injected into well 1, which may be air or steam or a mixture
of air and steam or hot water, it sweeps the formation to form the
expected tear shaped swept area 2 and ultimately the injected fluid
breaks through into production well 3. Once the thermal recovery
fluid has broken through at the production well, that phase of the
production operation is concluded and generally little or no
additional oil will be recovered by continuing injection of thermal
recovery fluid into well 1. If additional air pressurization wells
4 and 5 are drilled and unheated air is injected into wells 4 and 5
during the period when thermal recovery fluid is traversing through
the formation from injection well 1 to production well 3, the
formation between air pressurization wells 4 and 5 and production
well 3 will have been pretreated as a consequence of unheated air
injection into wells 4 and 5. Several benefits result from this
pretreatment process. The pressure gradients created around wells 4
and 5 confine the recovery fluid so as to avoid its loss into the
formation, and similarly avoid the movement of mobilized petroleum
from the formation away from the vicinity of production well 3.
Thus the pressure gradients assist in improving the thermal
efficiency and capture efficiency of the supplemental oil recovery
operation. In addition, a gas saturation is established in that
portion of the formation between wells 3, 4, and 5, which will
improve the receptivity of the oil formation to the subsequent
injection of thermal recovery fluid in the next phase of the
recovery program. Additionally, it has been discovered that
bituminous petroleum such as is found in tar sand deposits is
beneficiated by a prior contact with unheated air for a prolonged
period of time. Numerous benefits result from such prior contact,
including increased oil recovery efficiency and a reduction in the
pressure gradient between wells necessary to drive the fluid toward
the production well. Additionally, it has been observed that the
pretreatment wih unheated air causes an additional improvement in
the response of bituminous petroleum such as tar sands to steam
flooding where the principle mechanism for transporting viscous
petroleum through the porous formation involves the formation of a
low viscosity oil-in-water emulsion. In application of a steam
drive to a tar sand deposit which has not been pretreated with
untreated air, both oil-in-water emulsions and water-in-oil
emulsions are formed. Water-in-oil emulsions have relatively high
viscosities and require additional treatment in order to break the
emulsions, whereas oil-in-water emulsions are very low in viscosity
and are very readily resolved into their separate phases by
contacting the emulsion with a mineral acid. Pretreating the
bituminous petroleum with unheated air causes a preference for
oil-in-water emulsions which explains the reduction in pressure
required to drive the bituminous petroleum toward the production
well.
While the above described process contemplates the simplest method
of applying the process of my invention, ordinarily supplemental
oil recovery of the type wherein a thermal recovery fluid such as
steam or hot water or heated air for in situ combustion is injected
into the formation involves the use of a pattern in order to
achieve greater sweep efficiency. The most common type of pattern
is so called inverted five spot, such as is shown in FIG. 2. In a
simple five spot pattern, an injection well 6 is located in the
center of the square grid and four production wells 7, 8, 9 and 10
are located on the corners of the square. Thus steam is injected
into the central injection well and moves outwardly toward the four
production wells, sweeping nearly all of the area within the square
whose corners are defined by production wells 7, 8, 9 and 10. The
shape of the swept area in a conventional inverted five spot
pattern is approximately as is shown in FIG. 2 by dotted line 11.
It can be seen that the swept area cusps outward as the injected
fluid approaches the production well, with the result that not
quite all of the square pattern is swept by the fluid. Nonetheless,
relatively high sweep efficiency is realized. Frequently, the five
spot pattern is part of an even larger pattern in which there are
many contiguous five spot patterns. The performance of a field may
be analyzed by examining only the single five spot element,
however, and so only one five spot element is shown in FIG. 2.
An application of the process of my invention to a supplemental oil
recovery process employing a five spot pattern is shown in FIG. 2.
The air pressurization wells 11, 12, 13, 14, 15, 16, 17 and 18 are
drilled around production wells 7, 8, 9 and 10. Although the
spacing between the inner grid and the outer grid can vary, it is
convenient to make the spacing somewhat equal for reasons that will
be explained later.
In the pattern as shown in FIG. 2, when steam injection is
initiated into steam injection well 6, air pressurization may
similarly be initiated in wells 11-18. Injection may be initiated
simultaneously into all the wells, or it is sometimes satisfactory
to inject into only part of the wells initially, after which
unheated air injection is switched to the other wells. For example,
injection may initially be into wells 11, 13, 15 and 17 for a
period of time, after which injection is switched to wells 12, 14,
16 and 18.
The pressure at which air is injection into the air pressurization
wells surrounding the production wells may be maintained between
about 10% and about 90% of the pressure at which the thermal
recovery fluid is injected into injection well 6. I have found that
in an especially preferred embodiment, the pressure in the air
pressurization wells is maintained at approximately 50% of the
pressure at which steam is being injected into the steam injection
wells. Since production wells 7, 8, 9 and 10 are at a pressure much
lower than central injection well 6 and also lower than air
pressurization wells 11-18, there will be a positive pressure
gradient not only between central injection well 6 and production
wells 7, 8, 9 and 10, but there will also be a similarly positive
pressure gradient between air pressurization wells 11-18 and
production wells 7-10. Thus there will be some flow of air from air
pressurization wells into the production wells.
In one embodiment of the process of my invention, the pressure at
which unheated air is injected into air pressurization wells 11-18
is maintained at the lowest level which will give a slight
indication of gas being produced at production wells 7-10,
indicating that a slow movement of unheated air through the
formation is being accomplished. This can be facilitated by adding
a small amount of a readily detectable material to the injected air
to function as a tracer.
While the above described method of applying the process of my
invention has generally referred to the use of steam injection, it
is to be understood that it is not so limited. The same procedure
may be used in an in situ combustion operation, in which heated air
is injected into central injection well 6 to initiate a combustion
reaction within the formation, which propagates through the
formation toward production wells 7-10. Unheated air is similarly
injected into wells 11-18, which will not result in the same
combustion reaction as occurs within the central pattern, since the
oil temperature is never raised to a point at which the combustion
reaction is initiated. Once the in situ combustion reaction has
been initiated by heating the air being injected into well 6 or by
direct application of heat to the oil formation while injecting
unheated air, the supplemental heating step may be terminated and
the injection of unheated air into well 6 is sufficient to maintain
the in situ combustion reaction which propagates through the
formation toward production wells 7, 8, 9 and 10. Thus after the
initial ignition step, unheated air is being injected into well 6
and also unheated air is being injected at a lower pressure into
air pressurization wells 11-18; however, a totally different kind
of reaction is occurring as a consequence of injection of unheated
air into well 6 from that which is occurring as a consequence of
injection of unheated air into wells 11-18.
The above described process may similarly be used in the
application of a modified combustion process known as a controlled
combustion reaction, in which the temperature of the combustion
front propagating outwardly from injection well 6 is regulated by
the injection of water or steam simultaneously or intermittently
with the injection of air into the formation after the combustion
reaction has been initiated. This type of process appears to be
more suitable for use in recovering viscous asphaltic petroleum
from tar sand deposits than either steam flooding or in situ
combustion alone. Thus the application of the process of my
invention to a formation being exploited by means of controlled
combustion would entail in one example, the simultaneous injection
of steam and air into well 6 while unheated air is being injected
at a reduced pressure into wells 11-18 to maintain the desired
pressure gradients around production wells 7-10.
The process of my invention may also be used with other patterns,
such as a seven-well delta pattern, a hexagonal pattern, or other
arrangements of a plurality of production wells around one or more
central injection wells.
While air is the especially preferred fluid for injection into
pressurization wells 11-18, certain benefits of the process of my
invention may be realized by injecting gases other than air into
pressurization wells 11-18. For example, carbon dioxide, natural
gas, other gaseous hydrocarbons such as ethane, propane, or butane,
as well as inert gases such as nitrogen may be injected into wells
11-18 at a pressure below the pressure at which the thermal fluid
is being injected into central injection well 6, in order to create
the gas saturated zone and to establish the confining pressure
gradients around the production wells. The use of gases other than
air or oxygen containing gases will not achieve the low temperature
oxidation pretreatment of the bituminous petroleum as is achieved
when air is injected into the outer wells. Accordingly, the
especially preferred embodiment employs the injection of unheated
air or an oxygen containing gas into pressurization wells
11-18.
By the term "unheated air" it is meant that the air is not
deliberately heated prior to injection. Some heating occurs in the
compression of air, however. As used herein, unheated air means air
having a temperature below about 400.degree.F and preferably below
about 200.degree.F.
FIELD EXAMPLE
In order to demonstrate the operability of the process of my
invention, and further to supplement the disclosure contained
above, the following description of a field experiment is
presented.
A one-half acre five spot pattern was drilled in the Athabasca tar
sand deposit consisting of a central injection well and four
surrounding production wells essentially as shown in FIG. 2.
Similarly, eight air pressurization wells drilled around the small
pilot, with the expectation that these wells would later be used in
an expanded pilot, and so were completed so that they may serve as
air pressurization wells initially and as production wells in the
later stages of the operation. Well spacing was chosen so that
wells 12, 14, 16 and 18 defined a five acre pattern and wells 11,
13, 15 and 17 defined a 10 acre pattern. A mixture of steam and air
was injected into the central injection well 6, the ratio of steam
to air being approximately 0.4 barrels of steam (as water) per
thousand standard cubic feet of air. The injection rate was
increased from a fairly low initial level to the maximum rate at
which air and steam could be injected into the central injection
well, and was maintained in the later stages of the operation at a
fairly constant level of about 500,000 standard cubic feet of air
per day. While steam and air were being injected into central
injection well 6 for the purpose of causing a controlled combustion
reaction to propagate through the formation toward the four outer
production wells 7, 8, 9 and 10, air was injected into the outer
ring of air pressurization wells. Air was injected sequentially
into the eight outer air pressurization wells rather than
simultaneously in this particular pilot because of equipment
limitations. Nevertheless, during the course of the operation,
unheated air was injected into each of the outer wells for the
purpose of pretreating the formation between these outer
pressurization wells and the middle ring of production wells. After
the controlled combustion front reached the four production wells,
these wells were converted to steam-air injection wells and a
mixture of steam and air was injected into these four original
production wells simultaneous with the continued injection of steam
and air into the original central injection well. Outer wells 12,
14, 16 and 18 which are originally used as air pressurization wells
were converted to oil production wells, and oil recovery was
obtained from these outer wells. It was noted that the produced
fluid was predominantly in the form of a low viscosity oil-in-water
emulsion, and a relatively low pressure gradient was maintained
between the central injection wells and the outer production wells
in the second stage of the operation.
While my invention has been describes in terms of a number of
specific illustrative examples, it is not so limited since many
variations thereover will be immediately apparent to those persons
skilled in the related art without departing from the true spirit
and scope of my invention. Similarly, while several mechanisms have
been described for the purpose of explaining the benefits resulting
from the application of the process of my invention, it is not
necessarily represented hereby that these are the only or even the
principal mechanisms responsible for such benefits, and I do not
wish to be bound by any particular explanation of the mechanisms
involved. It is my desire and intention that my invention be
limited and restricted only by those limitations and restrictions
that appear in the claims appended immediately hereinafter
below.
* * * * *