U.S. patent application number 12/752645 was filed with the patent office on 2011-07-21 for accelerated start-up in sagd operations.
Invention is credited to Subodh Gupta, Claire Y. Hong, Patty Morris, Kirsten Pugh.
Application Number | 20110174488 12/752645 |
Document ID | / |
Family ID | 44276692 |
Filed Date | 2011-07-21 |
United States Patent
Application |
20110174488 |
Kind Code |
A1 |
Morris; Patty ; et
al. |
July 21, 2011 |
ACCELERATED START-UP IN SAGD OPERATIONS
Abstract
A method of initiating or accelerating the establishment of
fluid communication between horizontal wells located in a formation
of very limited fluid mobility, such as an oil sand at original
temperature or an infill well completed in an immobile hydrocarbon
region located between surrounding well patterns in which a
gravity-dominated recovery process is or has been operated.
Inventors: |
Morris; Patty; (Calgary,
CA) ; Hong; Claire Y.; (Calgary, CA) ; Gupta;
Subodh; (Calgary, CA) ; Pugh; Kirsten;
(Calgary, CA) |
Family ID: |
44276692 |
Appl. No.: |
12/752645 |
Filed: |
April 1, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61295324 |
Jan 15, 2010 |
|
|
|
61303862 |
Feb 12, 2010 |
|
|
|
Current U.S.
Class: |
166/305.1 |
Current CPC
Class: |
E21B 43/17 20130101;
E21B 43/16 20130101; E21B 43/2406 20130101 |
Class at
Publication: |
166/305.1 |
International
Class: |
E21B 43/16 20060101
E21B043/16 |
Claims
1. A method wherein a selected amount of solvent is injected at
sub-fracturing conditions (pressure or rate or both) and ambient
temperature into a first horizontal well located in an immobile
formation or reservoir, so as to accelerate fluid communication in
the formation or reservoir between the first horizontal well and a
second horizontal well with which the first horizontal well is not
in fluid communication.
2. The method of claim 1, wherein the solvent is xylene, benzene,
toluene, phenol or mixtures or derivatives thereof.
3. The method of claim 1, wherein the solvent is injected into
either the first horizontal well or the second horizontal well, or
into both the first horizontal well and the second horizontal
well.
4. The method of claim 1, wherein the immobile formation or
reservoir is an oil sand reservoir at original conditions.
5. The method of claim 4, wherein the original conditions includes
a bitumen or heavy oil density of about 12.degree. API or
heavier.
6. The method of claim 5, wherein the bitumen or heavy oil density
is about 15.degree. API or heavier.
7. The method of claim 1, wherein the selected amount of solvent is
a volume less than ten times the volume of the first horizontal
well completion.
8. The method of claim 1, wherein a further selected amount of
solvent is injected at sub-fracturing conditions and ambient
temperature into the second horizontal well.
9. The method of claim 8, wherein the further selected amount of
solvent is a volume less than ten times the volume of the second
horizontal well completion.
10. The method of claim 8, wherein the total of the selected amount
of solvent and the further selected amount of solvent is a volume
less than ten times the volume of the total of the first horizontal
well completion and the second horizontal well completion.
11. The method of claim 1, wherein the solvent is displaced into
the immobile formation or reservoir using a displacing fluid
sufficient to displace substantially all of the selected volume of
solvent into the formation or reservoir.
12. The method of claim 11, wherein the displacing fluid is a
non-condensing, non-oxidizing gas.
13. The method of claim 12, wherein the displacing fluid is
substantially nitrogen.
14. The method of claim 1 wherein the injected solvent is allowed
to remain resident in the immobile formation or reservoir for a
selected period of time before a subsequent recovery process is
implemented.
15. The method of claim 14, wherein the solvent is displaced into
the immobile formation or reservoir using a displacing fluid
sufficient to displace substantially all of the selected volume of
solvent into the formation or reservoir after the selected period
of time before the subsequent recovery process is implemented.
16. The method of claim 1 whereby, following application of the
method to establish inter-well communication, a subsequent recovery
process is implemented.
17. The method of claim 16, wherein the subsequent recovery process
is SAGD or other gravity-dominated recovery processes that involved
the use of solvents, either thermally or non-thermally.
18. The method of claim 1 wherein the first horizontal well is an
infill well that is completed in an immobile hydrocarbon region
located between surrounding well patterns of a gravity-dominated
recovery process.
19. The method of claim 18 wherein the immobile hydrocarbon region
is in a bypassed region, remaining between adjacent mobilized
hydrocarbon regions of a gravity-dominated recovery process.
20. The method of claim 18 wherein fluid communication is
established between the first horizontal well and an adjacent
mobilized hydrocarbon region of a gravity-dominated recovery
process.
21. The method of claim 18 wherein fluid communication is
established between the first horizontal well and an adjacent
common mobilized hydrocarbon region of a gravity-dominated recovery
process.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of priority of U.S.
Provisional Patent Application No. 61/295,324 filed Jan. 15, 2010
and U.S. Provisional Patent Application No. 61/303,862 filed Feb.
12, 2010, both of which are incorporated herein by reference in
their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to oil and gas production.
More particularly, the present invention relates to the recovery of
heavy oil or bitumen from, for example an oil sand or tar sand
deposit. More particularly, the present invention relates to a
method for starting up such operations in a gravity controlled
recovery system, such as Steam Assisted Gravity Drainage
(SAGD).
BACKGROUND OF THE INVENTION
[0003] Numerous patents, patent applications and technical papers
describe means of establishing fluid communication between
proximate horizontal wells that are located in porous media of
limited fluid mobility, such as an oil sand at original conditions.
However, as will be explained, none of these relies on or teaches
the key elements of the present invention to accomplish that
communication.
[0004] For example, U.S. Pat. No. 3,913,672 filed Oct. 15, 1973, by
J. C. Allen and D. A. Redford and titled "Method for establishing
communication path in viscous petroleum-containing formations
including tar sands for oil recovery operations" describes a method
to establish fluid communication in a viscous petroleum-containing
formation such as an oil sand. The method comprises "forming an
initial entry zone into the formation by means such as hydraulic
fracturing and propping, or utilizing high permeability streaks
naturally occurring within the formation, and injecting into the
propped fracture zone or high permeability streak a solvent for the
petroleum contained in the formation, said solvent being saturated
with a gas or containing appreciable quantities of gas dissolved
therein". In contrast to this, the present invention requires no
prior establishment or presence of permeable zone or streak.
Furthermore, the present invention, while using a solvent, requires
no dissolution in that solvent of a gas. Thus, the present
invention, in not requiring these well-known aids to fluid
conveyance in an oil sand or other formation of limited mobility,
is not only novel but also non-obvious.
[0005] The abstract of U.S. Pat. No. 3,706,341 to Redford, and
titled "Process For Developing Interwell Communication In A Tar
Sand", reads in part: "A hot, competent, permeable communications
zone, connecting injection and production wells completed in a tar
sand, is developed as follows: A cold, aqueous solution containing
sodium hydroxide and a non-ionic surfactant is injected into a
propped fracture system connecting the wells . . . . Bitumen is
slowly emulsified in the solution and removed through the fracture
system . . . ". The present invention involves none of the
chemicals, or chemical combinations, or chemical types described in
this patent. Also, Redford utilizes a prior means of communication,
described as a "propped fracture system connecting the wells"
whereas the present invention relies on no such prior communication
artifact.
[0006] U.S. Pat. No. 4,249,604 to Frazier and titled "Recovery
method for high viscosity petroleum" states that " . . . the
invention relates to oil recovery methods wherein heated aqueous
fluids are injected into directionally drilled injection wells
which are drilled radially inward towards central producing well .
. . ". The present invention differs materially from this patent in
both process and well configuration.
[0007] U.S. Pat. No. 4,301,868 filed Oct. 15, 1979 by G. Scherubel
et al and titled "Method using hydrocarbon foams as well
stimulants" states in the abstract that "This invention relates to
the use of silicone-induced hydrocarbon foams as well stimulants,
for example as illustrated by their use in fracturing well
formations, removal of paraffin in wells, removal of condensate
hydrocarbons from blocked gas wells, etc". The process of the
present invention differs materially from that of this patent and
specifically does not use foams.
[0008] U.S. Pat. No. 7,464,756 filed Feb. 4, 2005 by I. Gates and
A. Gutek and titled "Process for in situ recovery of bitumen and
heavy oil" includes as claim 1 in its entirety the following: "A
method to recover heavy hydrocarbons from an underground reservoir,
the underground reservoir being penetrated by an injection well and
a production well, the method comprising the steps of: (a)
injecting steam and a heavy hydrocarbon solvent into the injection
well over time, while producing reservoir hydrocarbons from the
production well; (b) transitioning from steam and heavy hydrocarbon
solvent injections to a lighter hydrocarbon solvent injection,
while continuing to produce hydrocarbons from the production well;
(c) continuing to inject the lighter hydrocarbon solvent while
producing hydrocarbons from the production well; and (d) enhancing
the solubility of solvents in steps (a) through (c) by monitoring
and adjusting reservoir pressure". The cited patent describes a
recovery process rather than an interwell communication technique.
That aside, the process initially requires the injection of steam
as a concomitant of the solvent injection "over time" while
producing from the production well. The present invention requires
no concomitant injection fluid along with the solvent, and involves
no step of concurrently producing at another well while the solvent
is being injected. Indeed, the present invention requires injection
of only the solvent with no injection of other fluids on either a
precedent, concomitant, or successor basis. It should also be noted
that, according to claims of the cited patent, solvent injection
occurs only at the injection well. In the present invention,
solvent is a means of establishing interwell communication and
occurs at either an injector or a producer or both.
[0009] Numerous patents involve well stimulation using a solvent in
which that solvent is heated by some means, such as the concomitant
injection of steam or prior heating of solvent, for example by
electrical means.
[0010] By way of illustration two of the patents that include these
features are:
[0011] U.S. Pat. No. 5,400,430 by J. Nenniger filed Jan. 21, 1994
and titled "Method for injection well stimulation". The process
involves electrical heating of a solvent prior to its injection
into the reservoir. Also, as the title implies, and as described
therein, the process is intended only for an injection well.
[0012] U.S. Pat. No. 7,363,973 by J. Nenniger and E. Nenniger filed
Feb. 2, 2005 and titled "Method and apparatus for stimulating heavy
oil production" describes in the abstract a process which "has the
steps of heating a solvent, such as propane, and then placing the
solvent into the extraction chamber at a temperature and a pressure
sufficient for the solvent to be in a vapor state in the chamber
and to condense on the extraction surface". Not only does the
patent describe the heating of the solvent, but it describes the
necessity for the solvent to be in a vapor state. The present
invention requires neither the prior heating of the solvent, nor
the requirement that it be in a vapor state nor the need for a
change of state.
[0013] Other processes involving solvent include U.S. Pat. No.
6,769,486 by G. Lim et al. filed May 30, 2002 and titled "Cyclic
solvent process for in situ bitumen and heavy oil production". This
patent involves injection of a solvent at a pressure sufficiently
high to cause formation dilation or pore fluid compression,
allowing solvent and hydrocarbons to mix at pore dilation
conditions, and then reducing the reservoir pressure so as to cause
a solvent gas drive. The present invention entails no dilation of
the formation, involves injection of the solvent strictly to
establish interwell communication, and does not function as part of
a solvent gas drive.
[0014] U.S. Pat. No. 5,607,016 by Butler filed November 1993 and
titled "Process and apparatus for the recovery of hydrocarbons from
a reservoir of hydrocarbons" describes in the abstract the process
as follows: "A method for the recovery of hydrocarbons from a
reservoir of hydrocarbons including injecting a hydrocarbon solvent
into the reservoir along with a displacement gas to mobilize
hydrocarbons in the reservoir of hydrocarbons; and producing
mobilized hydrocarbons from the reservoir of hydrocarbons. The
hydrocarbon solvent is injected along one or more predominantly
horizontal injection wells in the aquifer that are spaced from the
production well or wells. The hydrocarbon solvent is a hydrocarbon
solvent selected from the group consisting of ethane, propane
butane". The present invention differs materially from this patent.
According to the claims, the patent involves the use of a gas to
first establish a communications path, and then continued use of
gas as a concomitant of solvent injection. The present invention
requires no prior step, such as gas injection, to establish
communication, and involves injection into the reservoir of the
solvent alone, without any concomitant fluids. Also, one embodiment
of the present invention involves the injection of xylene, whereas
the Butler patent confines its specifications to a solvent from the
group consisting of ethane, propane, butane.
SUMMARY OF THE INVENTION
[0015] This invention pertains to a method of establishing or
accelerating fluid communication between horizontal wells located
in a formation of very limited fluid mobility, such as an oil sand
reservoir. The horizontal wells may be vertically displaced from
each other, for example as are the injector and producer in a SAGD
pattern. Or they may be staggered with respect to each other, for
example as when a horizontal infill well is situated in the region
between two surrounding SAGD well patterns.
[0016] The method of accelerating communication according to this
invention involves injecting a modest amount of solvent, one
embodiment of which is xylene, into a subject well. A subject well
is herein defined as a well that is located in a region of the
reservoir that has very limited fluid mobility and from which
communication is to be established with a target well by means of
solvent injection. Conversely, a target well is herein defined as a
well with which communication is to be established by means of
solvent injection into the subject well.
[0017] The solvent is injected via the subject well into the
reservoir at sub-fracturing pressures. Injection of the solvent may
be into any individual subject well or into any combination of
subject wells. After some time period of soak, and without the aid
of previously created flow channels at a subject well, such as
through fracturing or pre-injection of mobile fluids, and without
the aid of prior or concurrent thermal means to establish or
enhance communication at a subject well, such as steam or in situ
combustion or electrical heating, communication between a subject
well and a target well is established, notwithstanding the modest
volume of solvent injected at the subject well.
[0018] In some instances, the subject well and the target well may
both be situated in a region of immobile bitumen. One embodiment of
this instance involves a SAGD well pair that has not yet been
placed in operation. In this embodiment, the subject well might be
either the injector, or the producer, or both.
[0019] In other instances, the subject well may be situated in an
extensive region of immobile bitumen whose distal boundary is
defined, in part or in whole, by an adjacent region of mobile
bitumen. One embodiment of this instance involves an infill
horizontal well that is located within the unheated region between
adjacent operating SAGD horizontal well pairs. In this embodiment,
the infill well is the subject well and the target wells are those
located within a SAGD steam chamber or heated zone, which zone is
separated from the subject well by a region containing bitumen of
very limited mobility.
[0020] In the case of a new SAGD well pair, the communication thus
achieved is sufficient to then permit inception of a
gravity-dominated process, such as SAGD, or other gravity-dominated
processes such as those involving the use of solvents as part of a
thermal or non-thermal technique, without the need for additional
procedures or processes whose purpose is to further facilitate or
expedite inter-well communication, such as steam circulation in the
wells.
[0021] In the case of an infill well located within a region of
very limited fluid mobility that is situated between SAGD well
pairs, communication is thus achieved without the need for
additional procedures or processes and is sufficient to permit the
infill well to participate in the recovery process by acting as a
supplementary means of production.
[0022] In one aspect, the present invention provides a method
wherein a selected amount of solvent is injected at sub-fracturing
conditions (pressure or rate or both) and ambient temperature into
a first horizontal well located in an immobile formation or
reservoir, so as to accelerate fluid communication in the formation
or reservoir between the first horizontal well and a second
horizontal well with which the first horizontal well is not in
fluid communication.
[0023] In an embodiment of the present invention the solvent is
xylene, benzene, toluene, phenol or mixtures or derivatives
thereof. In an embodiment of the present invention the solvent is
substantially xylene.
[0024] In an embodiment of the invention, the solvent is injected
into either the first horizontal well or the second horizontal
well, or into both the first horizontal well and the second
horizontal well.
[0025] In an embodiment of the invention, the immobile formation or
reservoir is an oil sand reservoir at original conditions. In an
embodiment of the invention, the original conditions include a
bitumen or heavy oil density of about 12.degree. API or heavier. In
an embodiment of the invention, the original conditions include a
bitumen or heavy oil density of about 15.degree. API or
heavier.
[0026] In an embodiment of the invention, the selected amount of
solvent is a volume less than ten times the volume of the first
horizontal well completion.
[0027] In an embodiment of the invention, a further selected amount
of solvent is injected at sub-fracturing conditions and ambient
temperature into the second horizontal well. In an embodiment of
the invention, the further selected amount of solvent is a volume
less than ten times the volume of the second horizontal well
completion. In an embodiment of the invention, the total of the
selected amount of solvent and the further selected amount of
solvent is a volume less than ten times the volume of the total of
the first horizontal well completion and the second horizontal well
completion.
[0028] In an embodiment of the invention, the solvent is displaced
into the immobile formation or reservoir using a displacing fluid
sufficient to displace substantially all of the selected volume of
solvent into the formation or reservoir. In an embodiment of the
invention, the displacing fluid is a non-condensing, non-oxidizing
gas. In an embodiment of the invention, the displacing fluid is
substantially nitrogen.
[0029] In an embodiment of the invention, the injected solvent is
allowed to remain resident in the immobile formation or reservoir
for a selected period of time before a subsequent recovery process
is implemented. In an embodiment of the invention, the solvent is
displaced into the immobile formation or reservoir using a
displacing fluid sufficient to displace substantially all of the
selected volume of solvent into the formation or reservoir after
the selected period of time before the subsequent recovery process
is implemented.
[0030] In an embodiment of the invention, a subsequent recovery
process is implemented following application of the method to
establish inter-well communication. In an embodiment of the
invention, the subsequent recovery process is SAGD or other
gravity-dominated recovery processes that involved the use of
solvents, either thermally or non-thermally.
[0031] In an embodiment of the invention, the first horizontal well
is an infill well completed in an immobile hydrocarbon region
located between surrounding well patterns of a gravity-dominated
recovery process.
[0032] In an embodiment of the invention, the immobile hydrocarbon
region is in a bypassed region, remaining between adjacent
mobilized hydrocarbon regions of a gravity-dominated recovery
process.
[0033] In an embodiment of the invention, fluid communication is
established between the first horizontal well and an adjacent
mobilized hydrocarbon region of a gravity-dominated recovery
process.
[0034] In an embodiment of the invention, fluid communication is
established between the first horizontal well and an adjacent
common mobilized hydrocarbon region of a gravity-dominated recovery
process.
[0035] Other aspects and features of the present invention will
become apparent to those ordinarily skilled in the art upon review
of the following description of specific embodiments of the
invention in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] Embodiments of the present invention will now be described,
by way of example only, with reference to the attached Figures,
wherein:
[0037] FIG. 1 illustrates the method of the present invention
applied to a SAGD well pair;
[0038] FIG. 2 illustrates a section 2-2 of FIG. 1;
[0039] FIG. 3 illustrates the method of the present invention
applied to an infill well completed between adjacent SAGD well
pairs; and
[0040] FIG. 4 illustrates the method of the present invention
applied to an infill well completed adjacent a SAGD well pair.
DETAILED DESCRIPTION
[0041] Referring to FIGS. 1 and 2, a typical SAGD recovery system
10 is shown, having an injection well 20 for injecting steam and a
production well 30 for producing fluids completed in a immobile
formation or reservoir 40. A portion of the injection well 20 is
open to the immobile formation or reservoir 40 via an horizontal
injection well completion 50. Similarly, a portion of the
production well 30 is open to the immobile formation or reservoir
40 via a horizontal production well completion 60. These horizontal
well completions are typically perforations, slotted liner,
screens, or a combination thereof known to one skilled in the
art.
[0042] In order to establish fluid communication between the
injection well 20 and the production well 30 in an accelerated
manner, a selected amount of solvent is injected at sub-fracturing
conditions (pressure or rate or both) and ambient temperature into
either the injection well 20 or the production well 30 or both the
injection well 20 and the production well 30.
[0043] The selected amount of solvent may be a relatively small
volume, for example less than about ten times the volume of the
horizontal well completion. As an example, if the horizontal
production well completion 60 includes a 7 inch (approximately
0.180 m) nominal diameter slotted liner, 800 m long, the volume of
the horizontal production well completion 60 is approximately 20
cubic metres. In such a case, a volume of less than about 200 cubic
metres may be selected.
[0044] Referring to FIG. 3, after a period of time of operation of
the SAGD recovery system 10, a mobilized region 70a develops around
the injection well 20a and the production well 30a (and likewise a
mobilized region 70b develops around the injection well 20b and the
production well 30b etc.). However, a portion of the immobile
formation or reservoir 40ab remains between the adjacent well
pairs. In the case where the mobilized region 70a and the mobilized
region 70b merge or coalesce to form a common mobilized region
70ab, the portion of the immobile formation or reservoir 40ab
remaining may be referred to as a bypassed region 40ab.
[0045] An infill well 80 is completed in the immobile formation or
reservoir 40ab. A portion of the infill well 80 is open to the
immobile formation or reservoir 40ab via an horizontal infill well
completion 90. In order to establish communication between the
infill well 80 and the mobilized region 70a or the mobilized region
70b or both, or the common mobilized region 70ab (and thus to the
production well 30a or the production well 30b or both), a selected
amount of solvent is injected at sub-fracturing conditions
(pressure and flow rate or both) and ambient temperature into the
infill well. The selected amount or solvent may be less than about
ten times the volume of the horizontal infill well completion
90.
[0046] Referring to FIG. 4, after a period of time of operation of
the SAGD recovery system 10, a mobilized region 70 develops around
the injection well 20 and the production well 30. However, a
portion of the immobile formation or reservoir 40 remains adjacent
the well pair.
[0047] An infill well 80 is completed in the immobile formation or
reservoir 40. A portion of the infill well 80 is open to the
immobile formation or reservoir 40 via a horizontal infill well
completion 90. In order to establish communication between the
infill well 80 and the mobilized region 70 (and thus to the
production well 30), a selected amount of solvent is injected at
sub-fracturing conditions (pressure and flow rate or both) and
ambient temperature into the infill well. The selected amount or
solvent may be less than about ten times the volume of the
horizontal infill well completion 90.
[0048] As a means of displacing the solvent into the reservoir at
the subject well while minimizing the quantity of solvent used, a
chasing fluid may be used, although this is not essential. If a
chasing fluid is used, it does not enter the reservoir and
therefore does not participate in the process of accelerating fluid
communication. Typically the chasing or displacing fluid is a
non-condensing, non-oxidizing gas, such as nitrogen, sufficient to
displace most of the solvent into the formation.
[0049] The present invention relates to a method of establishing
communication between a horizontal well that is situated in a
hydrocarbon deposit of very limited mobility, such as an oil sand
or heavy oil at original temperature, and another well or region.
As such, the present invention provides a means of accelerating
start-up of a follow-up gravity-dominated recovery process such as
SAGD. In another aspect the present invention provides a means of
establishing communication between a horizontal well that is within
and surrounded by a region of immobile bitumen and a mobilized
region that is located at some distance from said horizontal well,
such as one or more operating SAGD well patterns.
[0050] This invention relies on the use of a solvent, one
embodiment of which is xylene, to mobilize the otherwise immobile
bitumen in the immediate vicinity of the horizontal wellbore or
wellbores. A designated volume, or slug, of solvent is injected at
a well and displaced through its horizontal section, or portions
thereof, into the reservoir.
[0051] The solvent or combination of solvents may be selected from
a wide variety of compounds. In one embodiment the solvent
comprises an organic solvent. In one embodiment the organic solvent
comprises an aromatic organic solvent. In one embodiment the
aromatic organic solvent comprises one or more of benzene, toluene,
phenol, xylene or their derivatives or mixtures. In one embodiment
the solvent is substantially xylene.
[0052] An aspect of the invention, and one which incorporates both
novel and non-obvious approaches, relates to the manner in which
the solvent is injected into the reservoir so as to establish
communication between the wells.
[0053] To this end, firstly, the solvent is injected at
sub-fracturing pressures, and no means are used to fracture, dilate
or otherwise alter the formation so that a preferential path or
channel is created in the reservoir. Secondly, the solvent is
injected at ambient conditions, is not heated, and no other heating
medium, such as steam, and no other displacing fluid such as a gas,
accompany the solvent, precede the solvent or follow the solvent
into the reservoir as part of the process of establishing
inter-well communication.
[0054] An option in applying the present invention is that, after
the solvent is displaced into the reservoir, it may be allowed to
reside, or soak, within the reservoir for a period of time.
[0055] Through the course of establishing inter-well communication
via the subject well, there is no need for any extraneous approach
to preparing the formation at said well, such as fracturing, or
formation heating, or injection of a precedent fluid, such as a
gas, to provide or facilitate the creation of a pre-existing
pathway for the solvent, or indeed injection of concomitant or
succeeding fluids.
[0056] A second novel and non-obvious aspect of this invention is
the absence of need for any means to augment mobility by heating
the solvent, or by relying on changes of phase through either
temperature or pressure or both.
[0057] A third novel and non-obvious aspect of this invention is
the relatively small volume of solvent slug used.
[0058] Solvent is generally very expensive. Therefore, while it may
always be possible to establish inter-well communication using a
sufficiently large volume of solvent, there will be some net
solvent losses to the reservoir, the cost of which will easily
negate any advantage provided by acceleration of recovery process
start-up. In the present invention, a volume of solvent is used
which is small relative to the available pore volume that must be
traversed in order to establish interwell communication but which
nevertheless achieves this communication.
[0059] The successful establishment of inter-well communication in
the manner consistent with this invention in a virgin oil sand
using small unheated slugs of xylene has been verified
experimentally at new SAGD wells. While many of the treatments that
were carried out involved xylene slugs placed or injected at both
the injector (injection well, being the upper well in a SAGD well
pair) and the producer (production well, being the lower well in a
SAGD well pair) at least one successful treatment included placing
or injecting the solvent into only the producer. As a further check
on the efficacy of the method, the xylene injection treatment
obviated the need, during follow-up SAGD operations, for
alternative means of establishing interwell communication such as
steam circulation in either the injector or producer, or both.
[0060] Simulations of the xylene injection process provided a
scientific basis for our salient field results. Simulation runs
showed that the path of the injected xylene outward from the
subject well is not isotropic. Instead, because of the density
difference between the xylene and the bitumen, or between the
xylene-bitumen blends that evolve as the xylene migrates within the
reservoir, and the bitumen, or between the xylene and the formation
water, or between the xylene-bitumen blends and the formation
water, there is a preferential upward movement of the xylene or
xylene-bitumen blend front. Thus whereas, if the flow geometry were
radial, certain limited volumes of xylene would fail to traverse
the distance between producer and injector, and might thereby fail
to establish inter-well communication, the situation in the
reservoir created by virtue of this invention, with its resulting
flow anisotropy, enables that same xylene volume to establish
inter-well communication.
[0061] In one embodiment the invention provides a method of
initiating or accelerating the establishment of fluid communication
between horizontal wells located in a formation of very limited
fluid mobility, such as an oil sand at original temperature or an
infill well completed in an immobile hydrocarbon region located
between surrounding well patterns in which a gravity-dominated
recovery process is or has been operated.
[0062] In the preceding description, for purposes of explanation,
numerous details are set forth in order to provide a thorough
understanding of the embodiments of the invention. However, it will
be apparent to one skilled in the art that these specific details
are not required in order to practice the invention.
* * * * *