U.S. patent application number 14/195518 was filed with the patent office on 2014-09-11 for single vertical or inclined well thermal recovery process.
This patent application is currently assigned to CENOVUS ENERGY INC.. The applicant listed for this patent is CENOVUS ENERGY INC.. Invention is credited to Simon D. GITTINS, Subodh GUPTA, Arun SOOD.
Application Number | 20140251608 14/195518 |
Document ID | / |
Family ID | 51486402 |
Filed Date | 2014-09-11 |
United States Patent
Application |
20140251608 |
Kind Code |
A1 |
GITTINS; Simon D. ; et
al. |
September 11, 2014 |
SINGLE VERTICAL OR INCLINED WELL THERMAL RECOVERY PROCESS
Abstract
The present disclosure describes a single well predominantly
gravity-dominated recovery process for producing viscous
hydrocarbons from a subterranean oil sands formation. The process
operates a single vertical or inclined well within a formation, the
wellbore having an injection means and a production means, the
injection means being positioned in the wellbore closer to the
surface than the production means. The process provides an area of
high mobility adjacent the production means. A mobilizing fluid is
injected through the injection means into the formation to mobilize
the viscous hydrocarbons in the formation while substantially
concurrently producing hydrocarbons through the production means.
The gravity dominated process may be SAGD and the present process
may be a single vertical or inclined well SAGD process.
Inventors: |
GITTINS; Simon D.; (Bragg
Creek, CA) ; GUPTA; Subodh; (Calgary, CA) ;
SOOD; Arun; (Calgary, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CENOVUS ENERGY INC. |
Calgary |
|
CA |
|
|
Assignee: |
CENOVUS ENERGY INC.
Calgary
CA
|
Family ID: |
51486402 |
Appl. No.: |
14/195518 |
Filed: |
March 3, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13785747 |
Mar 5, 2013 |
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14195518 |
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Current U.S.
Class: |
166/272.3 |
Current CPC
Class: |
E21B 43/2406 20130101;
E21B 43/2408 20130101 |
Class at
Publication: |
166/272.3 |
International
Class: |
E21B 43/24 20060101
E21B043/24 |
Claims
1. A method of producing viscous hydrocarbons from a subterranean
oil sands formation, comprising the steps of: i. operating a
vertical or inclined well within a formation, the well having an
injection means and a production means, the injection means being
positioned in the well closer to the surface than the production
means, and wherein the injection means is positioned in the
wellbore in the absence of an induced fracture in the formation
adjacent the injection means; ii. providing an area of high
mobility in the formation adjacent the production means; iii.
injecting a mobilizing fluid through the injection means into the
formation, to mobilize the viscous hydrocarbons in the formation;
and iv. substantially concurrently producing the viscous
hydrocarbons through the production means; v. wherein the viscous
hydrocarbons are produced using a predominantly gravity-dominated
process.
2. The method of claim 1 wherein the formation adjacent the
injection means has an absence of an area of high mobility.
3. The method of claim 1 wherein the injection and production means
are isolated from each other within the well.
4. The method of claim 1 wherein the injecting and/or producing is
done on a continuous or an interrupted basis.
5. The method of claim 1 wherein providing an area of high mobility
comprises mobilizing the hydrocarbons in the formation in an area
adjacent the production means to form the area of high
mobility.
6. The method of claim 5 wherein mobilizing the hydrocarbons
comprises introducing heat into the area.
7. The method of claim 6 wherein introducing heat into the area
comprises using electric heating, electromagnetic heating, or
injecting heated fluids into the area.
8. The method of claim 7 wherein the heated fluids comprise steam,
hot water, solvent, and a combination thereof.
9. The method of claim 1 wherein providing an area of high mobility
comprises altering the matrix structure of the area.
10. The method of claim 9 wherein altering the matrix structure
comprises dilation of the formation area.
11. The method of claim 1 wherein providing the area of high
mobility comprises replacing native fluids in the area with high
mobility fluids.
12. The method of claim 11 wherein high mobility fluids comprise
water, light hydrocarbons, non-condensing gases and combinations
thereof.
13. The method of claim 1 wherein providing the area of high
mobility comprises removing formation material in the area and
filling the area with high permeability material.
14. The method of claim 13 wherein removing formation material
comprises mining, drilling or under-reaming the formation to create
a cavity.
15. The method of claim 13 wherein the high permeability material
comprises gravel.
16. The method of claim 1 wherein the area having high mobility is
a pre-existing area of high mobility.
17. The method of claim 1 wherein the injected mobilizing fluid is
steam, light hydrocarbon, hot water, or a mixture thereof.
18. The method of claim 1 wherein the gravity-dominated recovery
process is steam-assisted gravity drainage (SAGD).
19. The method of claim 1 further comprising maintaining a liquid
level in the formation to avoid introduction of uncondensed
injected mobilizing fluids into the production means.
20. The method of claim 1 wherein steam is initially injected
through both the injection and production means to mobilize the
viscous hydrocarbons and establish communication in the formation
between the injection and production means.
21. The method of claim 1 wherein the mobilizing fluid is
circulated through the well to mobilize the viscous hydrocarbons
and establish communication in the formation between the injection
and production means.
22. The method of claim 1 wherein the viscous hydrocarbons are
selected from the group consisting of bitumen, heavy oil, and
unmobilized hydrocarbons.
23. The method of claim 8 wherein the solvent comprises one or more
of a C.sub.3 to C.sub.10 solvent.
24. The method of claim 23 wherein the solvent is hexane.
25. The method of claim 23 wherein the heated fluids comprise up to
12 wt % solvent.
26. The method of claim 23 wherein the heated fluids comprise the
steam and the solvent which are injected substantially
simultaneously or alternating.
27. The method of claim 12 wherein the high mobility fluids
comprise one or more of a C.sub.3 to C.sub.10 solvent.
28. The method of claim 27 wherein the solvent is hexane.
29. The method of claim 27 wherein the high mobility fluids
comprise up to 12 wt % solvent.
30. The method of claim 29 wherein the high mobility fluids
comprise the steam and solvent which are injected substantially
simultaneously or alternating.
31. The method of claim 1 wherein the mobilizing fluid further
comprises one or more of surfactants and non-condensing gases.
Description
FIELD
[0001] The present disclosure relates generally to oil recovery
processes and particularly to thermal recovery and thermal/solvent
recovery processes that may be applied in viscous hydrocarbon
reservoirs, and specifically in oil sands reservoirs.
BACKGROUND
[0002] Among the deeper, non-minable deposits of hydrocarbons
throughout the world are extensive accumulations of viscous
hydrocarbons. In some instances, the viscosity of these
hydrocarbons, while elevated, is still sufficiently low to permit
their flow or displacement without the need for extraordinary
means, such as the introduction of heat or solvents. In other
instances, such as in Canada's bitumen-containing oil sands, the
hydrocarbon accumulations are so viscous as to be practically
immobile at native reservoir conditions. As a result, external
means, such as the introduction of heat or solvents, or both, are
required to mobilize the resident bitumen and subsequently harvest
it.
[0003] A number of different techniques have been used to recover
these hydrocarbons. These techniques include steam flood, (i.e.,
displacement), cyclic steam stimulation, steam assisted gravity
drainage, and in situ combustion, to name a few. These techniques
use different key mechanisms to produce hydrocarbons.
[0004] Commercially, the most successful recovery technique to date
in Canada's oil sands is Steam Assisted Gravity Drainage (SAGD),
which creates and then takes advantage of a highly efficient fluid
density segregation, or gravity drainage, mechanism in the
reservoir to produce oil. A traditional system that is a
concomitant of the SAGD process is the SAGD well pair, which
typically consists of two generally parallel horizontal wells, with
the injector vertically offset from and above the producer.
[0005] SAGD was described by Roger Butler in his patent CA
1,130,201 issued Aug. 24, 1982 and assigned to Esso Resources
Canada Limited. Since that time, numerous other patents pertaining
to aspects and variations of SAGD have been issued. Also, many
technical papers have been published on this topic.
[0006] In U.S. Pat. No. 5,014,787 filed Aug. 16, 1989, Duerksen of
Chevron describes a single vertical well system, with detailed
focus on the tubing-casing-packer configuration within the
wellbore. This system utilizes a "drive fluid". Generally drive
fluids are used in non-SAGD systems to drive or "push" the
hydrocarbons to a producer well. This is in contrast to
gravity-dominated processes such as SAGD which use gravity as the
key mechanism in the production of the hydrocarbons. Duerksen's
system and associated method utilize a "drive fluid" to establish
near-wellbore communication within the reservoir between an upper
set of injection perforations and a lower set of production
perforations and does not mention gravity drainage or a
gravity-dominated process.
[0007] In U.S. Pat. No. 5,024,275 filed Dec. 8, 1989, to Anderson
et al, assignee Chevron, a similar system is described as that in
U.S. Pat. No. 5,014,787 but the vertical wellbore hydraulics are
modified somewhat. Also, mention is made of maintaining a liquid
level within the reservoir such that uncondensed fluids are not
inadvertently produced. However, as with U.S. Pat. No. 5,014,787,
reference is made to a "drive fluid". There is no mention of a
gravity-based recovery mechanism.
[0008] U.S. Pat. No. 5,238,066 filed Mar. 24, 1992 to Beattie et
al., assignee Exxon, pertains to a method introduced in the later
stages of a cyclic steam stimulation (CSS) operation, and involves
alternating periods of steam injection into upper perforations
followed by hydrocarbon production from lower perforations. There
is no mention or implication of a gravity-dominated recovery
process.
[0009] In the paper titled "Lloydminster, Saskatchewan Vertical
Well SAGD Field Test Results", published in the Journal of Canadian
Petroleum Technology, November 2010, Volume 49, No. 11, by Miller
& Xiao of Husky Energy, a field experiment involving a single
vertical well SAGD-type operation is described. The reservoir in
which the experiment was conducted involved a viscous oil, but with
considerably lower native viscosity (i.e., higher mobility) than
the types of bitumen present in the oil sands. The authors
indicated that the test "demonstrated that a single vertical well
SAGD configuration could be successfully completed and operated".
For reasons that the authors attributed to geology and initial
fluid distribution within the reservoir setting, the authors noted
that "Field performance of single vertical SAGD Well 4C11-1 was not
as good as expected", and suggested that single vertical well SAGD
methodology could be "used to help determine if sufficient vertical
permeability exists for the low-pressure gravity-based horizontal
well SAGD process to be successful". That is, the authors proposed
that their single vertical well SAGD methodology could be applied
as a diagnostic technique for determining vertical permeability
within the reservoir rather than as an effective recovery
process.
[0010] Other vertical well configurations have been proposed. For
example, X-Drain.TM., a trademarked and patented concept by
GeoSierra/Halliburton involves a single vertical well that employs
a SAGD-type process. Emanating from the vertical well are a number
of highly permeable vertical planes, similar to vertical hydraulic
fractures, with the fractures propped or held open by a permeable
propping agent. Each such plane has its own azimuth so that the
effect, when viewed from above, is geometrically similar to a hub
(the vertical well) and spokes (the induced multi-azimuth vertical
planes). Steam is injected into the upper portion of the well and
moves outward through the highly permeable propping agent contained
within these multi-azimuth vertical planes to mobilize the bitumen
at the faces of each plane.
[0011] For many decades, Imperial Oil has practiced a cyclic steam
stimulation process at their Cold Lake oil sands operation using
vertical and inclined wells. The viability of the recovery process
depends on the use of formation fracturing during the injection
cycle to create a largely vertical fracture that spans a
significant vertical portion of the formation. While flow of heated
fluids to the well during the production cycle takes advantage of
gravity drainage to a limited degree, the principal means of
bringing the fluids to the wellbore at commercial flow rates during
the production phase of the cycle is the imposition of a pressure
gradient (i.e., the creation of a pressure sink at the wellbore
during its production phase). Thus, while the recovery process
employed by Imperial Oil at Cold Lake requires vertical fractures
and, as such, includes an element of gravity drainage, flow and
displacement via an imposed pressure gradient is the dominant
recovery mechanism.
[0012] Canadian patent application CA 2,723,198 filed Nov. 30, 2010
to Shuxing, assignee ConocoPhillips, describes a vertical well
recovery process which can include a gravity-dominated mechanism.
The patent application describes a well configuration involving a
single well with an upper and a lower set of openings or
perforations. It further requires the creation of two horizontal
fractures--one opposite the upper injection interval and one
opposite the lower producing interval. However, there are
additional costs and other disadvantages to fracturing so it may
not be feasible or desirable for a particular formation.
[0013] There therefore remains a need in the industry for an
effective oil recovery process using a single vertical or inclined
well and a gravity dominated recovery process such as SAGD.
SUMMARY
[0014] It is an object of the present disclosure to obviate or
mitigate at least one disadvantage of previous systems.
[0015] In one aspect, the present disclosure provides a method of
producing viscous hydrocarbons from a subterranean oil sands
formation using a single well gravity-dominated process, comprising
the steps of operating a single vertical or inclined well, the
wellbore having an injection means and a production means, the
injection means being positioned in the wellbore closer to the
surface than the production means; providing an area of high
mobility adjacent the production means; injecting a mobilizing
fluid through the injection means into the formation to mobilize
the viscous hydrocarbons in the formation; and substantially
concurrently producing hydrocarbons through the production means;
wherein the viscous hydrocarbons are produced using a predominantly
gravity-dominated process. In one aspect, the injection and/or
production operations may be continuous. In one aspect, the
injection and/or production operations may proceed on an
interrupted basis. In one aspect, the injection and production
means are isolated from each other in the wellbore. In one aspect,
the area in the formation adjacent the injection means is absent an
induced fracture.
[0016] In a further aspect, the step of providing an area of high
mobility may comprise mobilizing the hydrocarbons around the
production means to form the area of high mobility. Mobilizing the
hydrocarbons may include introducing heat into the area. This may
be done by electric or electromagnetic heating or by injecting
heated fluids into the area. Alternatively, providing the area of
high mobility may comprise altering the matrix structure of the
area such as through dilation of the formation area. Alternatively,
providing an area of high mobility may comprise replacing native
fluids in this area with high mobility fluids such as water, light
hydrocarbons, non-condensing gases and combinations thereof.
Alternatively, providing an area of high mobility comprises
removing reservoir material in the area and filling the area with
high permeability material such as gravel. In a further
alternative, the area of high mobility may comprise a naturally
occurring or pre-existing area of high mobility.
[0017] In a further aspect, the gravity-dominated recovery process
is steam-assisted gravity drainage (SAGD). In a further aspect, the
gravity-dominated recovery process is a solvent or solvent-assisted
process. In a further aspect, the single well is a vertical or
substantially vertical well or an inclined well.
[0018] Other aspects and features of the present disclosure will
become apparent to those ordinarily skilled in the art upon review
of the following description of specific examples in conjunction
with the accompanying figure.
BRIEF DESCRIPTION OF DRAWINGS
[0019] Aspects of the present disclosure will be described by way
of example only with reference to the attached figure.
[0020] FIG. 1 is a depiction of one example of a single well
completion of the present disclosure.
DETAILED DESCRIPTION
[0021] The present disclosure provides a method or process for the
recovery of viscous hydrocarbons from a subterranean reservoir
using a single vertical or inclined well, the performance of which
is improved by the inclusion of certain features as described
herein. The recovery process is a gravity-dominated process but may
also include drive or displacement mechanisms to a lesser
degree.
[0022] The hydrocarbons produced using the single well gravity
dominated recovery process described herein are immobile
hydrocarbons or mobile hydrocarbons which benefit from a thermal
recovery process, i.e. while the hydrocarbons may have some
mobility, it may not be sufficient to be commercially effective for
production or the mobility may be increased with a thermal recovery
process to improve production. In one aspect, the hydrocarbons are
heavy oil and/or bitumen.
[0023] In one aspect, the recovery process is a gravity dominated
process. By gravity dominated process is meant a process whose flow
mechanisms are predominantly gravity controlled and whose
techniques of operation are largely oriented toward ultimately
maximizing the influence of gravity control because of its inherent
efficiency. It is understood by those ordinarily skilled in the art
that a gravity dominated process, while relying principally on a
gravity drainage mechanism to govern fluid displacement, does not
preclude the use of subsidiary fluid flow processes, such as
convective displacement. One example of a gravity dominated process
is steam assisted gravity drainage (SAGD).
[0024] In a further aspect, the recovery process is a thermal or
thermal and solvent process. In such a process, steam, light
hydrocarbons, hot water, or suitable combinations thereof may be
used as the injection fluid. Further, these injection fluids, such
as steam and light hydrocarbons, may be injected as a mixture or as
a succession or alternation of fluids. Examples of light
hydrocarbons include C.sub.3 to C.sub.10 hydrocarbons such as
propane, butane, pentane, and hexane. The light hydrocarbon may be
a solvent, or solvent mixture, which will exist substantially in
liquid form at recovery process conditions within the reservoir,
thereby facilitating its eventual drainage by gravity, along with
mobilized oil, to the basal region of the vertical well. In other
words, a substantial portion of the solvent, or solvent mixture,
will possess a vapor pressure which is lower than that of the steam
with which it is co-injected or within whose environment it is
introduced, thereby substantially behaving as a less volatile fluid
than the steam. In one embodiment, the injected fluid includes an
amount of solvent, or solvent mixture, of up to 12 wt %. In another
embodiment, the amount of injected solvent is up to 5 wt % and in
the alternative, in the range of 4 to 10 wt %.
[0025] The method uses a single vertical or inclined well. In one
aspect, a vertical well implies a well that is substantially or
predominantly vertical, but may include sections or segments that
are not vertical. Analogously, reference to an inclined well
implies a well that is substantially or predominantly inclined to
the vertical at an angle less than 90 degrees, but which is not
either substantially vertical or substantially horizontal, yet may
include sections or segments that are vertical or horizontal.
[0026] Further, a single well may include an individual wellbore
whose openings to the reservoir have been configured to allow for
both injection and production, as would be contemplated in a
gravity-dominated recovery process, such as a SAGD operation.
[0027] The single vertical or inclined well may also include
equipment, such as multiple strings of tubulars, as well as
packers, valves and pumps, which may be necessary to operate the
well in this mode.
[0028] In the case of a horizontal well SAGD process, it is well
known that, because of the low density of steam relative to the
other fluids in its environment, the growth of the SAGD chamber is
upward and eventually outward. That is, given a sufficiently thick
reservoir, the steam chamber grows and ascends dramatically beyond
the vertical elevation of the injector. However, in the downward
direction, there is little significant growth of the chamber below
the horizontal producer, and modest outward growth of the chamber
at the level of the producer when compared to the growth at or near
the top of the chamber. As a consequence, for the fluids flowing
downward in the SAGD process, the chamber shape is such that there
is convergence of flow in the vicinity of the producer. In
principle, this convergent flow geometry tends to restrict flux
rates into the producer and reduce productivity. However, in the
case of a horizontal well process, this convergence, and the
concomitant flow restriction is compensated for by the extended
length of the well (e.g., 800m). Thus, flux rates over any unit
length interval along the horizontal well may be small whereas the
overall well production rate may nevertheless be significant over
the active length of wellbore, so that the horizontal well SAGD
process is commercially feasible.
[0029] In the case of a single vertical well employing a
gravity-dominated process, such as SAGD, where steam is injected
through an upper open interval in the wellbore and fluids are
produced from a lower open interval in that same wellbore, there is
a strong three-dimensional convergence of the flow toward and into
the bottom producing interval. This convergent flow geometry
encircles the entire vertical wellbore in the vicinity of the
producing interval, forming a cone-like shape and thereby markedly
restricting productivity. This contrasts with a horizontal
producing well configuration in which the convergence of stream
lines is only two-dimensional (i.e., trough-like along the length
of the horizontal well) so that the relative productivity loss is
less.
[0030] A highly convergent flow geometry, and its restriction on
flow, is particularly harmful to a gravity drainage process such as
SAGD. Specifically, in the case of a single vertical well, it will
result in an accumulation of liquids in or around the lower regions
of the well. That accumulation is capable of quenching or killing
the steam chamber.
[0031] This disclosure, an aspect of which is illustrated
schematically in FIG. 1, provides a method for altering the
abovementioned conical convergent flow geometry in the case of a
single vertical or inclined well being used to carry out a
gravity-dominated recovery process, such as SAGD, so that the flow
restriction, and its attendant high pressure losses and deleterious
effects on the steam chamber, are ameliorated. Furthermore, it does
so without requiring vertical fractures, multi-azimuth vertical
planes, or induced fractures adjacent the injection means, such as
those described in the prior art.
[0032] As shown in FIG. 1, a well is provided in a subterranean
formation having an overburden 1, a pay zone 2 with viscous
hydrocarbons to be produced, and an underburden 3. A first upper
set of perforations 4 are positioned near the top of the pay zone 2
and a second lower set of perforations 6 are positioned near the
bottom of the pay zone. Within a single well, a conduit 7 for
injecting fluids, such as steam, into the formation extends to the
upper set of perforations 4. A conduit 8 for producing fluids from
the formation extends to the lower set of perforations 6. The
conduits 7 and 8 may be tubing or other means known in the art. The
conduits 7 and 8 (and appropriate perforations) are positioned
within the well and/operated under conditions so that injected
fluids from conduit 7 are not produced directly from conduit 8
through the wellbore rather than injected into the formation. This
may require, for example, that conduit 7 and 8 be positioned a
suitable distance apart or they may be isolated within the well by
means known in the art, such as a packer 5 shown in FIG. 1. The
positioning of conduit 7 and 8 or use of other means to isolate
them will depend on the particular well and formation and is within
the knowledge of the skilled person.
[0033] The present method is a method of recovering hydrocarbons
from a reservoir using a single well gravity-dominated recovery
process in the presence of a high mobility zone 9. The high
mobility zone 9 is located substantially opposite the producing
interval of the single vertical or inclined well. The high mobility
zone 9 may be either pre-existing or artificially established.
Operation of the recovery process occurs at a single well and, as
illustrated in this aspect, involves injecting steam into the
reservoir through the upper set of perforations 4 and producing
mobile and mobilized fluids from the reservoir through the lower
set of perforations 6, all under conditions that allow gravity
drainage to predominate.
[0034] The operation of the recovery process at the single well
includes injecting steam through the upper set of perforations 4
while substantially concurrently producing mobile hydrocarbons from
the producer at the lower set of perforations 6. Substantially
concurrently means that while it is preferred that the hydrocarbons
will be produced at the same time that steam or other fluids are
injected into the formation, it is recognized that this is not
always possible. Therefore, the injecting and producing may be
sequential or alternating, and may be continuous or interrupted,
during part of the recovery process. However, it is preferred that
the injection and production will operated mainly on a concurrent
basis.
[0035] Reference is made to a high mobility zone as a feature of
the present method. Mobility, as used here, accords with
traditional reservoir engineering usage and as such is defined as
the permeability of a porous medium to a resident fluid divided by
the resident fluid viscosity. The high mobility zone that is a
feature of the present method involves a zone that is substantially
horizontal in orientation (e.g., a layer or a pancake-like
structure) located in the generally lower portion of the reservoir,
preferably opposite the producing perforations, where those
perforations will be typically located in the lower portion of the
reservoir. The shape of the high mobility zone can be irregular so
long as it functionally mimics or approximates a layer or
pancake-like structure, as one ordinarily skilled in the art would
understand. Thus, the present method avoids not only the
installation of multi-azimuth vertical planes, as specified in the
X-Drain technology, but also eliminates the need for high pressure
vertical fracturing, such as that utilized by Imperial Oil at Cold
Lake. It further avoids the requirement for an induced fracture
adjacent the injection means, as described by Shuxing.
[0036] If a basal high mobility zone is not already present, it can
be artificially induced or created. The exact means of creating
this zone will depend on a number of factors including the specific
formation and viscosity of the hydrocarbons. It is well within the
knowledge of the skilled person to select an appropriate method to
create the high mobility zone. For example, the high mobility zone
can be created by removing the reservoir material, as for example
by mining or by drilling and under-reaming, and filling the cavity
thus created with high permeability material such as, for example,
gravel. If the basal portion of the reservoir initially contains,
as its native fluid, a high saturation of relatively immobile
bitumen, then a basal high mobility zone can be created using known
techniques for increasing the mobility of resident bitumen, such as
for example by heating or solvent addition. For example, the
formation may be heated using electric heating, electromagnetic
heating, or injecting heated fluids into the formation. The high
mobility zone can be created by dilation of the reservoir or other
such techniques which alter matrix structure. The high mobility
zone can also be created by replacing native fluids in this lower
region with high mobility fluids, such as water, light hydrocarbons
or non-condensing gases, or combinations thereof. Any one or more
of these methods as well as other known methods can be used by a
skilled person to create the high mobility zone as required in a
particular formation.
[0037] More specifically, in a further aspect, a horizontally
oriented pancake-like high mobility zone that surrounds a vertical
well is to be emplaced within the reservoir, using techniques such
as those recited above, at a level that is opposite the producing
interval. The dimensions of this high mobility zone, and the
make-up of the fluids which reside in its pores, can be selected by
those ordinarily skilled in the art by means of simulation or
developed guidelines. Subsequently, when a gravity-dominated
recovery process, such as SAGD, is employed, steam enters the
reservoir from the wellbore through an upper open interval of the
single vertical well. In the present method, as the SAGD chamber is
established, the tendency of the mobilized bitumen to flow along a
downward convergent path to the producing interval and thereby be
subjected to excessive pressure loss will be countered by the
presence of the basal high mobility zone, which will provide a more
energy efficient conduit for the mobilized bitumen to reach the
producing interval at the wellbore. In so doing, the presence of
the basal high mobility zone either eliminates or mitigates the
tendency of the converging fluids to quench or otherwise impede the
progress of the steam chamber.
[0038] Prior art recovery methods may use a naturally occurring
basal high mobility zone, such as a basal water zone, as a means of
injecting or introducing heat into the reservoir. However, the
prior art methods do not utilize a high mobility feature, whether
natural or created, for purposes of production or for purposes of
enhancing the operation of the overlying gravity drainage
mechanism.
[0039] If a naturally occurring high mobility zone is present at or
near the base of the reservoir, then certain characteristics of
that zone will determine whether there is a need for alterations to
the geometry or state of that zone so that it may be used as the
high mobility zone in the present recovery process. For example, to
ensure that hot downward-draining bitumen from the SAGD process
does not cool excessively when it encounters a naturally occurring
basal high mobility zone, it may be desirable to replace some
portion of a native fluid, or the native fluids, resident in this
basal high mobility zone with one or more different fluids. These
replacing fluids can be selected for reasons of inherent
properties, such as heat capacity, density, viscosity or
miscibility with bitumen. Alternatively, they can be selected for
reasons of fluid state, such as would be the case if it was desired
to replace a cold native fluid with a similar or alternative fluid,
or fluids, that will impose a higher temperature on the high
mobility zone and thence on the downward-draining bitumen.
[0040] When a gravity drainage process is operated using a single
vertical or inclined well process, the presence of a high mobility
zone, as described above in various aspects, will prevent or
ameliorate flow effects that are deleterious to productivity.
Specifically, in the case of SAGD recovery process, the presence of
a high mobility zone will facilitate the drainage of oil and water
to the producing interval of the well. Correspondingly, in the
absence of such a high mobility zone, the highly convergent flow
patterns associated with a single vertical or inclined well process
will result in hold up of the oil and water, and consequent
quenching or reduction in size of the steam chamber.
[0041] CA 2,732,198 requires the use of two fractured zones, one
adjacent to the injector and one adjacent to the producer. However,
it has been found by the present inventors that two high mobility
zones are not necessary. Having only one high mobility zone
adjacent the producer is sufficient to aid in hydrocarbon
production using the vertical well as disclosed herein. Further, it
is not necessary to fracture the formation. A high mobility zone
adjacent to the producer can be created using other methods and
still produce beneficial results in recovering hydrocarbons.
[0042] The present disclosure requires only a single high mobility
feature, either created or naturally present, opposite the
producing interval. The additional required feature in CA 2,723,198
(Shuxing) of a fracture created opposite an upper set of
perforations would allow steam injected at these upper perforations
to move some lateral distance outward from the wellbore. However,
it is believed that the present disclosure achieves this same
lateral spreading without need of an additional fracture, as
required by Shuxing. Specifically, as observed in numerous SAGD
field operations within the oil sands, and as demonstrated in
simulations, steam injected at a set of perforations with no
associated fracture will not only move upwards, but will also flare
laterally outwards, thereby providing a broad region within which
bitumen can be mobilized. Accordingly, it is believed that, through
the development of a mobilized zone or steam chamber at, above and
laterally outward from the upper perforations at the wellbore, the
present disclosure achieves lateral extension of mobility within
the reservoir without need of a fracture opposite the upper
perforations.
[0043] Furthermore, in the event that the present disclosure is
preceded by a start-up acceleration technique known within the
industry, such as for example xylene injection or dilation, a zone
of enhanced mobility surrounding the well between the upper and
lower openings or perforations will be created. With this zone of
enhanced mobility in place in the present invention, it is believed
that the already superfluous or marginal value of the upper
fracture in CA 2,723,198 will be accentuated.
[0044] As already noted above, the disclosed recovery process may
also be applied at an inclined well. In the case of an inclined
well configuration, it may be desirable to modify, especially in a
horizontal aspect, the geometry of the high mobility zone, firstly
with respect to the concentricity or eccentricity of its placement
relative to the point or region over which it intersects the
wellbore, and secondly with respect to its compass orientation.
Thus, in the case of an inclined well, it may be advantageous to
ensure that horizontal placement of the high mobility zone is
eccentric with respect to its intersection with the well and that
the high mobility zone is oriented along a compass direction such
that the high mobility zone is underneath, and can serve as a
catchment for, the downward draining fluids from the overlying
active zone or chamber created by the thermal recovery process,
(e.g., SAGD or a Solvent Aided Process).
[0045] Of course, the decision to employ, and the manner in which
one employs, a vertical or inclined well in a single well SAGD
process may be influenced by local lithology, as well as by
operating considerations. This would include the inclination of the
well itself with respect to the vertical, the placement of the
injection and production openings along the wellbore and the
geographic placement and horizontal extent of the basal high
mobility zone. With respect to the placement of the injection and
production openings, it should be clearly understood that the
present process contemplates the possibility of not just a single
set of injection openings and a single set of production openings.
Rather, a multiplicity of sets of injection and of production
openings is also contemplated, as dictated by needs recognizable to
those ordinarily skilled in the art, including but not limited to
needs associated with equipment, operations or lithology as well as
considerations associated with fluid flow and displacement.
[0046] It is noteworthy that the present process reflects a well
configuration, whether vertical or inclined, wherein the producing
interval is substantially opposite the basal high mobility zone. As
such, the open or completion interval at the producer is at or
below the base of the pay, so that the gravity mechanism can be
operative vertically throughout the pay. This is in contrast to the
situation in horizontal well SAGD where the horizontal producer is
not situated at the very base of the pay but rather is typically
located some distance above the base of pay and, as such, may not
recover substantial amounts of underlying oil.
[0047] The foregoing description has been presented in terms of
gravity-dominated thermally based recovery processes, such as SAGD.
However, it should be understood that gravity-dominated
solvent-assisted processes, such as for example the Solvent Aided
Process (SAP), which employs a suitable hydrocarbon solvent, or
combinations thereof, in conjunction with steam, will also function
beneficially with the present process. Still another
gravity-dominated recovery process alternative involves introducing
a suitable solvent and water into the reservoir and heating the
mixture as appropriate.
[0048] Other additives that may also be employed in the practice of
the present method include non-condensing gases and
surfactants.
[0049] Also, with a gravity-dominated process, such as SAGD, a
start-up process is required to established communication between
the injector and producer wells. A skilled person is aware of
various techniques for start-up processes, such as for example hot
fluid wellbore circulation, the use of selected solvents such as
xylene, or the application of geomechanical techniques such as
dilation. Techniques such as these can also be employed as a means
of accelerating start-up in the present recovery process.
[0050] Reference is made to exemplary aspects and specific language
is used herein. It will nevertheless be understood that no
limitation of the scope of the disclosure is intended. Alterations
and further modifications of the features described herein, and
additional applications of the principles described herein, which
would occur to one skilled in the relevant art and having
possession of this disclosure, are to be considered within the
scope of this disclosure. Further, the terminology used herein is
used for the purpose of describing particular embodiments only and
is not intended to be limiting, as the scope of the disclosure will
be defined by the appended claims and equivalents thereof. All
publications, patents, and patent applications mentioned in this
specification are herein incorporated by reference to the same
extent as if each individual publication, patent or patent
application were each specifically and individually indicated to be
incorporated by reference.
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