Note: Descriptions are shown in the official language in which they were submitted.
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SINGLE VERTICAL OR INCLINED WELL
THERMAL RECOVERY PROCESS
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
August 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.
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=
[0006] In U.S. patent 5,014,787 filed August 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. patent 5,024,275 filed December 8, 1989, to Anderson et al,
assignee
Chevron, a similar system is described as that in US 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
US 5,014,787, reference is made to a "drive fluid". There is no mention of a
gravity-based
recovery mechanism.
[0008] U.S. patent 5,238,066 filed March 24, 1992 to Beattie et at., 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".
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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-
DrainTM, 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 November 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.
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[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.
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[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] Figure 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
CA 02844345 2014-03-03
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 C3 to C10 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.
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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
Figure 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.
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[0032] As shown in Figure 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 Figure 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
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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.
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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
CA 02844345 2014-03-03
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.
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[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
12
(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.
13
Date recu/Date Received 2020-04-20
