Note: Descriptions are shown in the official language in which they were submitted.
CA 02794205 2012-11-02
IMPROVED SAGD OIL RECOVERY METHOD UTILIZING MULTI-
LATERAL PRODUCTION WELLS AND/OR COMMON FLOW
DIRECTION
FIELD INVENTION
The present invention relates to a bitumen or heavy oil extraction process,
and more
particularly to improved SAGD oil recovery methods for producing oil or
bitumen from
subterranean hydrocarbon deposits using injection of a flowable medium
comprising a heated
fluid or a viscosity-reducing agent.
BACKGROUND OF THE INVENTION
In a SAGD (Steam Assisted Gravity Drainage) method for recovering bitumen or
viscous oil from a hydrocarbon-containing formation, a horizontal injector
well is drilled
relatively high in a region of the formation under development. A parallel
horizontal production
well is drilled low in the region of the formation under development. The
production well has a
horizontal portion typically situated 5-6 meters directly below the horizontal
portion of the
injector well, and parallel thereto, and which like the horizontal portion of
the injector well,
extends into the hydrocarbon-containing layer. Steam is injected into the
hydrocarbon formation
via the horizontal portion of the injector well, and oil within the formation
which becomes heated
and thereafter becomes mobile, by force of gravity and/or pressure drains
downwardly in the
formation where it is collected in the horizontal portion of the production
well and produced to
surface.
Typically, the injector well and the collector well of a SAGD well pair are
drilled from one
end of a development region within the formation, and typically from the same
well pad at one
end of such development region.
Where a large formation is being exploited, numerous SAGD well pairs
comprising
parallel, vertically aligned injector and producer wells are aligned in side-
by side juxtaposed
position, with each producer well being positioned vertically below a paired
injector well.
- 1-
CAL LAW\ 1865667\1
CA 02794205 2012-11-02
Large capital costs are incurred in not only drilling the injector and
producer wells, but
also in obtaining the necessary equipment, such as steam generating equipment
and piping,
for such SAGD method of recovery.
Clearly, therefore, in light of these large capital costs, it is advantageous
to maximize oil
production from such wells to ensure the greatest return on investment, and
further recover
such oil as quickly as possible once these capital costs have been incurred to
thereby obtain
the quickest return on investment.
Accordingly, a real need exists to improve upon the existing SAGD method to
realize
these objectives.
In addition, problems may arise in existing SAGD well pairs during the life of
such wells,
such as "sanding in" of production wells, or leakage of steam from the
injector wells directly into
the production well without flowing firstly through the desired areas in the
development regions
which are desired to be heated to mobilize oil therein. Both of these problems
significantly
reduce the volume and recovery rates of oil from such wells and/or may
possibly prevent further
recovery of economic amounts of oil even though a significant amount of heavy
oil may still
remain in the region of the formation under development.
Accordingly, a real need further exists for an effective manner of
recuperating or
rejuvenating production wells in SAGD well pairs which are not operating to
maximum potential,
in order to recover as much of the oil from the region under development and
avoid loss of
invested capital.
SUMMARY OF THE INVENTION
The present invention comprises modifications to the standard SAGD method for
recovery of oil from a formation, wherein such method is modified in
configuration and/or in
manner of drilling to result in lower capital cost (for same number of drilled
wells) , or
increased rate of production, or both.
Specifically, in a first embodiment of the present invention, it has been
experimentally
and surprisingly found that if the ratio of the number of collector wells to
injector wells in the
above standard SAGD configuration of wells is increased, for the same number
of wells as
- 2-
CALLAW \ 1865667\ 1
CA 02794205 2012-11-02
would be drilled for the standard SAGD configuration and under typical
conditions as exist in
heavy oil formations, an increase in both the rate of production of oil and
the cumulative oil
produced can be obtained over the figures that would otherwise be obtained
from the
conventional SAGD configuration.
As a result of such aforementioned discovery confirming the desirability for
drilling
proportionately more collector wells in relation to injector wells, the
present invention, in an
alternative or additional aspect, provides for a modified SAGD method
comprising the drilling
of a plurality of horizontal collector (production) wells from a common shaft
using multi-lateral
well drilling techniques, to be paired with a single injector well. In such
manner the benefit of
increased number of horizontal collector wells in relation to injector wells
can be realized, but at
a fraction of the cost of drilling separately such additional number of
horizontal collector wells
by being able to economize in using as common to all such wells the vertical
or inclined portion
of the production well.
In addition, in a further alternative or additional modification to the
standard SAGD
configuration of injector/producer well pairs wherein the injector well and
production well are
each drilled from a common end of a region of a formation under development,
the present
invention comprises a modification of such method to reduce leakage of steam
from the injector
well into the production well and improve the rate and amount of oil produced.
Specifically, the
present invention, in an alternative embodiment, comprises the modification to
the convention
SAGD oil recovery process by instead drilling the production well from an end
of a region the
formation under development opposite that end at which the injector well has
been drilled. In
such manner, undesirable leakage of steam from the injection well into the
production
(collector) well(s) can be reduced resulting in an increase in rates and
amounts of oil produced.
The above separate modifications to the standard SAGD methodology can be
employed
separately, or in combination.
In a further alternative embodiment, the present invention provides for a
method of
improving/rejuvenating the performance of a standard SAGD well pair.
Specifically, an existing
SAGD well pair can have its production of oil increased, particularly in
instances where the
horizontal portion of the production well has become "sanded in" and/or there
is extensive
leakage of steam from the injector well into the collector well which has
resulted in reduced or
no production from the collector well, by the drilling of one or more
additional
collector(production) wells, wherein said collector well(s) is/are drilled
from an opposite end of
- 3-
CAL LAW\ 1865667\1
CA 02794205 2012-11-02
the region of the formation under development than the end which the original
injector and
collector well were drilled. This result has further been experimentally
confirmed by in-field
testing, specifically as identified in SPE publication CSUG/SPE SPE-149239-PP
entitled "A
New SAGD Well Pair Placement; a Field Case Review" presented at the Canadian
Unconventional Resources Conference held in Calgary, Alberta, Canada, 15-17
November
2011. Specifically, by using this method of rejuvenating the standard SAGD
well pair, the rate
of oil produced from the new collector well which is drilled from an opposite
end of the region
of the formation under development has been found to produce increased rates
and amounts of
oil production as compared to the rates and amounts of oil production in
comparison with output
obtained from the original previously-drilled collector well. It is suspected
and theorized,
without being limited to such theory, that by providing the production well at
an opposite end of
the region of development that the steam injector well, the direction of flow
of the steam in the
injector well and the oil in the production(collector) wells are made the
same, thereby aligning
high pressure regions in each of the production well and injector well (and
likewise thereby
aligning low pressure regions in each of the production well and injector
well) and leakage of
steam via "fingering" in the formation from the heel end of the injector well
into the production
well is avoided or at least reduced. Such method of rejuvenation of existing
standard SAGD
well pairs may be further modified to take advantage of the above discovery of
using increased
ratio of production wells to injector wells, and the lower capital cost of
drilling such wells using
multi-lateral drilling techniques, if a plurality of collector wells are
drilled and/ or if a plurality of
production (collector) wells are drilled from an opposite end of a region of
the formation under
development than the original injector well was drilled. Due to the
elimination or reduction of
"leakage", improved CSOR (cumulative steam-oil recovered ration) will also be
realized.
Accordingly, a first object of the present invention is to provide for
increased production
and rates of production in SAGD applications
A second object of the present invention is to reduce capital costs , as
compared to
standard SAGD methods..
A third object of the invention is to provide an improved SAGD method of oil
recovery
where instances of undesirable leakage (ie "short-circuiting") of steam
directly from injector well
to the producer well are reduced or avoided, to thereby improve the overall
performance
(cumulative oil, and rate of production) of a SAGD well pair, and reduce the
CSOR (cumulative
steam-oil recovered ratio).
- 4-
CAL LAW \ 1865667\1
CA 02794205 2012-11-02
A still further alternative object of the invention is to provide for a manner
of rejuvenating
SAGD well pairs to avoid loss of capital when recovery rates from the producer
well have
dropped below economic recovery rates, but where significant quantities of oil
still remain in the
region of the formation under development.
The above are non-limiting objects of the present invention, and may be used
in
combination, or separately.
The above objects to are not to be construed as necessarily representing,
jointly or
severally, objects attained by each and every aspect of the present invention.
To realize one or more of the above objects, in a first broad aspect of the
present
invention, the present invention comprises modifying the production well-
drilling step of a
standard SAGD method of recovery to comprise drilling a plurality of multi-
lateral horizontal
collector wells parallel to the injector well, and extending horizontally
outwardly from the vertical
well portion of the production well, but with each horizontal collector well
positioned
immediately below such injector well. In a preferred embodiment one of the
multi-lateral
collector wells is positioned immediately vertically below the horizontal
portion of the steam
injector well.
Specifically, in such first broad aspect of the present invention, such
invention
comprises an improved method for recovering oil or bitumen from a development
region of a
hydrocarbon-containing subterranean formation, comprising the steps of:
(i) drilling an injection well having a vertical or inclined portion and
further having a
substantially horizontal portion extending into said development region
adapted for injecting a
medium comprising a heated fluid or viscosity-reducing agent into said
development region;
(ii) drilling a production well having a common downwardly extending inclined
or vertical
shaft portion, and , using multi-lateral well-drilling techniques, drilling a
plurality of substantially
parallel horizontal collector wells extending outwardly therefrom into said
development region,
each of said parallel horizontal collector wells extending substantially
parallel and proximate to
said horizontal portion of said injection well but spaced vertically below
said horizontal portion
of said injection well;
(iii) injecting a medium comprising a heated fluid such as steam or a
viscosity-reducing
agent into said injection well and thereby into the development region via
said horizontal
- 5-
CAL_LAW \ 1865667 \ 1
CA 02794205 2012-11-02
portion thereof; and
(vi) collecting, via said plurality of horizontal collector wells, oil from
said development
region that has flowed into said collector wells, and producing said oil to
surface.
The plurality of horizontal collector wells are positioned vertically below
the injector well,
and parallel thereto and to each other, but may be at the same or different
individual depths
below the injector well.
The term "heated fluid" is herein defined and intended to comprise any
flowable
medium which may be heated, such as steam, heated water, or the like, which
can transfer
heat into a region of development of a formation containing oil, and by
transferring such heat to
oil or bitumen in the formation, reduce the viscosity of such oil and/or cause
such oil to become
mobile and,via existing pressure in the formation and/or gravity, be caused to
flow downwardly.
The term "viscosity-reducing agent" is herein defined and intended to comprise
a
flowable medium which reduces the viscosity of oil or bitumen in the formation
so as to cause
such oil or bitumen to become mobile. Numerous viscosity-reducing agents for
reducing the
the viscosity of oil and bitumen in a formation are well known to persons of
skill in the art, and
include , but are not limited to, flowable mediums such as naptha, diesel,
carbon dioxide
gas, non-condensable gases such as methane or ethane, or mixtures thereof.
In a preferred embodiment of the above method, the plurality of collector
wells
comprises three parallel collector wells, comprising a first horizontal
collector well drilled
immediately below said horizontal portion of said injection well and parallel
thereto, and two
horizontal production wells drilled respectively on each side of the first
collector well, in
mutually parallel relation, but laterally spaced therefrom.
In a further embodiment, the vertical or inclined portion of the injection
well, and the
inclined or vertical shaft of the production well, are one and the same. This
allows for further
economy in drilling of the wells in that only one vertical or inclined shaft
need to be drilled, and
by using multi-lateral drilling techniques , as further discussed herein, the
horizontal injector
well and horizontal collector wells may be drilled laterally outwardly from
such inclined or
vertical portion.
In a further refinement of the above method, said vertical or inclined portion
of said
injection well is drilled at one end of said development region, and said
inclined or vertical shaft
- 6-
CAL LAW \ 1865667\1
CA 02794205 2012-11-02
of said production well is situated at a mutually opposite end of said
development region, so
that the medium enters said development region at one end thereof and flows in
a first
direction along said horizontal injection well to reduce viscosity of oil in
the development
region, and said common inclined or vertical shaft of said production well is
drilled at an
opposite end of said development region so that oil which collects in said
horizontal collector
wells flows within said horizontal collector wells in the same direction as
said first direction,
namely in the same direction as steam in said injector well.
In a further alternative broad aspect of the present invention, the present
invention
comprises an improved oil recovery method for recovering oil from a
development region of a
hydrocarbon-containing subterranean formation, comprising the steps of:
(i) drilling, at one end of said development region, an injection well, having
a vertical or
inclined portion, and further having a horizontal portion extending into said
development
region and adapted for injecting a medium comprising a heated fluid or
viscosity-
reducing agent into said development region;
(ii) drilling, via a common inclined or vertical shaft, at a mutually opposite
end of said
development region, at least one
production well having at least one horizontal
collector portion substantially parallel and proximate to said horizontal
portion of said
injection well but spaced vertically below said horizontal portion of said
injection well and
extending into said development region;
(iii) injecting a flowable compressible medium comprising a heated fluid or a
viscosity-
reducing agent into said injection well and into the development region via
said
horizontal portion of said injection well; and
(vi) collecting within said at least one horizontal collector portion oil
within said formation
that has flowed into said collector portion, and producing such oil to
surface;
wherein said medium enters said development region at one end thereof via said
injector well and flows in a first direction along said horizontal portion of
said injection
well; and
wherein oil which collects in said at least one horizontal collector portion
of said
production well flows within said horizontal portion in a direction the same
as said
medium in said injection well.
-7-
CAL LAW11865667\1
CA 02 7 942 05 2 012 -11- 02
The medium used in this embodiment is typically a compressible fluid, since
the
problem with leakage typically arises due to non-uniform pressure along the
injector well which
is exacerbated when compressible fluids are used. Drilling the production well
at an end of the
region of development opposite that end which the injector well is drilled is
adapted to overcome
or alleviate such problem, and thus this aspect of the invention will most
suitably be adapted for
applications where a compressible fluid, such as steam, is used.
In a preferred embodiment of the above further aspect of the invention,
wherein step (ii)
comprising drilling at least one production well at an opposite end of the
development region
having at least one horizontal collector portion comprises drilling, using
multi-lateral drilling
techniques, a plurality of horizontal collector wells extending outwardly from
said vertical or
inclined shaft portion, each of said plurality of collector wells having a
horizontal portions
substantially parallel and proximate to said injection well , but spaced
vertically below said
horizontal portion of said injection well; and collecting within said
horizontal portion of each of
said collector wells oil from said formation that has flowed into said further
collector wells, and
producing said oil to surface via said common inclined or vertical shaft.
In a further embodiment, three(3) collector wells are drilled-a first
collector well directly
below and parallel to said injector well, and the second and third collector
wells positioned on
each side of said first collector well, in mutually parallel relation, but
laterally spaced therefrom.
In a still further separate aspect of the present invention, the invention
comprises a
method for improving recovery from a hydrocarbon-containing formation having
an already-
drilled and existing well pair comprising an injector well and a production
well, said injector
well having a horizontal portion extending into a region of the formation
under development,
said production well having vertical or inclined shaft portion and a
horizontal portion
substantially extending outwardly therefrom and parallel to said horizontal
portion of said
injector well but spaced vertically below said horizontal portion of said
injector well, wherein said
injector well and production well are drilled from a same first end of a
region of the formation
under development, comprising the steps of:
(i) drilling, using multi-lateral well drilling techniques, from said vertical
or inclined shaft
portion of said production well, at least one further horizontal well,
hereinafter referred to as a
collector well, extending outwardly therefrom and parallel to said horizontal
portion of said
injector well, said collector well spaced vertically below said horizontal
portion of said injector
well.
- 8-
CAL LAW \ 1865667\1
CA 02794205 2012-11-02
In an alternative embodiment for improving recovery from a hydrocarbon-
containing
formation, namely for improving recovery from a hydrocarbon-containing
formation having an
already-drilled SAGD well pair comprising an steam injector well and a
production well, said
injector well having a horizontal portion extending into a region of the
formation under
development, said collector well having a horizontal portion substantially
parallel to said
horizontal portion of said injector well but spaced vertically below said
horizontal portion of said
injector well, wherein said injector well and collector well are drilled from
a same first end of a
region of the formation under development, such invention comprises the steps
of:
(i) drilling, at a second opposite end of said region of the formation under
development
proximate a toe portion of said injector well, and via a common inclined or
vertical shaft,
at least one further production well having a horizontal portion substantially
parallel to
said injector well but spaced vertically below said horizontal portion of said
injector well
and extending into the development region;
(ii) injecting a medium such as a heated fluid or viscosity-reducing agent
into said
injector well and thereby into the region of the formation under development
via said
horizontal portion of said injector well; and
(iii) collecting within said horizontal portion of said at least one further
production well,
oil from said formation that has flowed into said further production well, and
producing
said oil to surface.
In a preferred embodiment of such still further aspect, - said above step (i)
of such still
further aspect of the present invention comprises:
drilling a plurality of production wells said at least one further collector
wells, each of
said plurality of production wells having a horizontal portion substantially
parallel and proximate
to said injector well , but spaced vertically below said horizontal portion of
said injector well;
and-collecting within said horizontal portion of each of said plurality of
production wells heated
oil from said formation that has flowed into said further collector wells; and
producing said oil to surface via said common inclined or vertical shaft.
In an alternative preferred embodiment of the embodiment for improving
recovery from
an already-drilled SAGD well pair, such comprises:
- 9-
CAL LAW\ 1865667\1
CA 02794205 2012-11-02
drilling, at said second opposite end of the region under development and
using multi-
lateral drilling techniques, a production well having a common inclined or
vertical shaft and a
plurality of horizontal portions extending outwardly therefrom in the form of
parallel collector
wells substantially parallel to said injector well but spaced vertically below
said horizontal
portion of said injector well and extending into the development region; and
collecting within said horizontal portion of each of said collector wells, oil
from said
formation that has flowed into said further collector wells, and producing
said oil to surface via
said common inclined or vertical shaft.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, which illustrate one or more exemplary
embodiments
and are not to be construed as limiting the invention to these depicted
embodiments:
Fig. 1 is a perspective view of a steam assisted gravity drainage
configuration of the
prior art, comprising a series of mutually parallel, paired injector and
collector wells;
Fig. 2a is a perspective view of a first embodiment of the present invention,
comprising
a single upper injection well and multi-lateral collector wells as offshoots
of a single vertical or
inclined production well shaft;
Fig. 2b is cross-section along plane A-A of Fig. 2a;
Fig. 3 is a perspective view of another embodiment of the present invention,
where the
injector well and collector wells are each drilled at mutually opposite ends
of a development
region of a formation, and the direction of flow of the injected steam is in
the same direction as
the direction of flow for the collected oil in the region under development;
Fig. 4a is a perspective view of a further refinement of the present
invention, comprising
a plurality of multi-lateral collector wells drilled from a single vertical
shaft, and a single injector
well, where the injector well and collector wells are each drilled at mutually
opposite ends of a
development region of a reservoir and the direction of flow of the injected
steam is in the same
direction as the direction of flow for the collected oil in the region under
development;
Fig. 4b is a cross-section along plane B-B of Fig. 4a;
Fig. 6 a is a perspective view of a further embodiment of the present
invention,
comprising a plurality of injector wells drilled from a common vertical shaft
and a similar or dis-
- 10-
CALLAVA1865667\1
CA 02794205 2012-11-02
similar plurality of collector wells likewise drilled from a common vertical
shaft, wherein in such
further embodiment the injector wells and collector wells are each drilled
from mutually opposite
ends of a development region of a reservoir and the direction of flow of the
injected steam is in
the same direction as the direction of flow for the collected oil in the
region under development;
Fig. 5b is a cross-section taken along plane C-C of Fig. 5b;
Fig. 6 is a cross- section of prior art existing SAGD well pair configuration
used in
computer simulation for obtaining baseline computer simulation results for
comparative
purposes of production rates and cumulative oil produced for such a
configuration, such results
shown graphically in Fig.'s 8 & 9 by the line "SAGD";
Fig. 7 is a cross-section of a modified configuration of the present invention
of SAGD
well pairs of lesser capital cost (where multi-lateral well drilling
techniques are used for drilling
the collector wells) to the configuration of Fig. 6, having multi collector
wells, for purposes of
comparing the production rates and cumulative oil produced for such
configuration as compared
to baseline results from the configuration of Fig. 6 , such results obtained
shown graphically in
Fig.'s 8 & 9 by the line "ML-SAGD";
Fig. 8 is a graph of the experimentally-modelled oil production rate over time
using
STARS computer simulation program, extrapolated into the future, for SAGD well
pairs having
the configuration shown in Fig. 6 (Example 1A) & Fig. 7 (Example 1B);
Fig. 9 is a graph of the experimentally- modelled cumulative oil produced over
time,
using STARS computer simulation program, for SAGD well pairs pairs having the
configuration
shown in Fig. 6 (Example 1A) & Fig. 7 (Example 1 B);
Fig. 10 is a schematic cross-sectional view of a method of the present
invention for
rejuvenating or restoring oil production from SAGD well pairs which have
ceased to be
uneconomical;
Fig. 11 is a view along plane D-D of Fig. 10;
Fig. 12 is a schematic cross-sectional view of a further embodiment of a
method of the
present invention for rejuvenating or restoring oil production from SAGD well
pairs which have
ceased to be uneconomical;
Fig. 13 is a view along plane E-E of Fig. 10;
- 11-
cm. LAW\ 1865667\1
CA 02794205 2012-11-02
Fig. 14 is a graph of the baseline results, namely the rate of initial oil
production versus
time (cubic meters per day) from production well 13, for a SAGD well pair of
Example 2;
Fig. 15 is a graph of the rate of resulting oil production over time (cubic
meters per day)
after drilling new production well I3A, in respect of the SAGD configuration
described in
Example 2 having an added collector well, wherein the direction of steam flow
and the direction
of oil flow in the collector well is the same; and
Fig. 16 is a graph of cumulative oil production (in cubic meters) as a
function of time
(days) comparing the 13-14 collector-injector well pair of Example 2 with the
13A-I4 collector
injector well pair of the SAGD configuration of Example 2.
DETAILED DESCRIPTION OF THE PRIOR ART AND PREFERRED EMBODIMENTS OF
THE PRESENT INVENTION
-First Embodiment
Fig. 1 shows a perspective view of a steam assisted gravity drainage
configuration 1 of
the prior art, comprising a series of steam injector wells 3 having
perforations therein (not
shown) for injecting steam 6 into a development region 10 of an underground
hydrocarbon-
containing formation . Injector wells 3 possess respectively parallel
horizontal portions 2
extending into a development region 10 of the formation
A corresponding number of
production wells 4 are provided with substantially horizontal portions 5
thereof positioned
directly vertically below respective horizontal portions 2 of the steam
injector wells 3, but
parallel to the horizontal portions 2 of the steam injector wells 3.
Heated oil 9 within the development region 10 of the formation which has
become
heated drains downwardly in direction of arrows 9 and flows into horizontal
portion 2 of the
production wells 4 via perforated screens therein (not shown), where such oil
9 thereafter
flows in direction 11 when being drawn along production well 4 and being
produced to surface.
Horizontal portions 2 of steam injector wells 3 contain steam 6 at a high
pressure HP
proximate the heel 7 of the injector wells 3, but at a lower pressure LP
proximate each of the
toe regions 8 of the injector wells 3. Conversely, oil 9 in horizontal
portions of production wells 4
is typically at its lowest pressure LP proximate heel region 21 of the
production wells 4 while
at its highest pressure HP proximate toe region 22 of each of production well
4, as shown in
Fig. 1.
- 12-
CALLAW \ 1865667\1
CA 02794205 2012-11-02
Disadvantageously with this prior art configuration of SAGD injector wells 4
and
producer wells 3 shown in Fig. 1, due to the highest pressure of the steam 6
in injector well 3
being at the heel 7 thereof and the lowest pressure in the horizontal portion
5 of the production
well 4 being likewise at the heel 21 thereof, there is a very strong tendency
(and it is an all-to-
common occurrence) for high pressure steam 6 at the heel 7 of the injector
wells 3 to "short
circuit" and, via finger-like fissures 20 in the development region 10,
undesirably flow directly
into the heel region 21 of the production well 4, thereby failing to be
injected into the
development region 10 along the length of horizontal portion 2 of the steam
injector wells 3 and
accordingly not serving the intended purpose of heating oil 9 in the
development region 10.
Substantial losses in efficiency of the SAGD process result and high SOR
(Steam ¨Oil
Recovered ratio) are accordingly caused.
In order to minimize the foregoing problem, Fig. 3 shows a first embodiment of
the
present invention, illustrating a modified SAGD configuration 100 and a
modified SAGD method
for recovering oil from region 10 of a formation being developed. As may be
seen, an injector
well 30 is drilled at one end 60 of the region 10 of the formation under
development. Injector
well 30 has a vertical or inclined portion 31 and a substantially horizontal
portion 32.
In accordance with such first embodiment, at least one production well 51 is
drilled at a
mutually opposite end 62 of region 10 under development. The at least one
production well 51
has an inclined or vertical shaft portion 50 and a horizontal collector
portion 52 positioned
substantially parallel and proximate to the horizontal portion 32 of injector
well 30 but spaced
vertically below said horizontal portion 31 and extending into the development
region 10.
Pressurized steam 6 is injected into injector well 30 and into the development
region 10
of a hydrocarbon-containing formation, via apertures (not shown) in horizontal
portion 32 of
injector well 30. Oil 9 which has become heated drains downwardly and flows
into the horizontal
collector portion 52 via apertures therein such as slotted screens or the like
(not shown), and is
thereafter produced to surface.
Advantageously, by drilling the at least one production well 51 at a mutually
opposite
end 62 of the region 10 under development than an end 60 at which said
injector well 30 is
drilled, steam 6 is able to be injected along horizontal collector portion 32,
with the highest
steam pressure HP being at heel end 7 of injector well 30 and with the lowest
steam pressure
LP being at the toe end 8 ( due to pipe losses along horizontal portion 32 of
injector well 30).
Similarly with the horizontal collector portion 52 , due to oil 9 being
withdrawn from heel end 21
-13-
CAL LAW\ 1865667\1
CA 027 94205 2012-11-02
thereof, the lowest pressure LP of oil 9 in such collector portion 52 is at
heel end 21, while the
highest pressure HP is at toe end 22. With such configuration the pressure
differential between
the horizontal portion 32 of the injector well 30 and the parallel horizontal
portion 52 of
production well is reduced, resulting in more uniform injection of steam 6
into region 10 along a
length of horizontal portion 32 of injector well 30 and the tendency for steam
to directly "short
circuit" from a region of high pressure to a region of low pressure in the
horizontal collector
portion of production well 51 is greatly reduced.
-Alternative Embodiment
Fig. 2a & Fig. 2b illustrate an alternative embodiment 101 of the invention
comprising a
method of SAGD recovery wherein the number of production wells has been
increased in
proportion to the number of injector wells, which modification has been
experimentally found for
typical formation conditions and for the same total number of wells drilled as
per a typical prior
art SAGD well pair configuration, to increase production rates and total
production (see
Example 1B compared to Example 1A herein, below).
Specifically, such modification to the prior art SAGD methods comprises
drilling, as per
prior art SAGD methods, a single injector well 30, having a horizontal portion
31 with a series of
apertures 33 therein to allow injection of steam into a region 10 in the
formation under
development.
Thereafter, however, rather than a single production well being drilled in
relation to the
single injector well 30, a plurality of substantially parallel horizontal
collector wells 52', 52", and
52" are drilled, extending parallel to the horizontal portion 31 of the
injector well 30, but spaced
vertically below such horizontal portion 31 of injector well 30, as best shown
in Fig. 2b.
In a preferred embodiment, in order to reduce the capital cost of such
modified SAGD
configuration, the plurality of horizontal collector wells 52', 52", and 52"
wells are drilled using
multi-lateral well drilling techniques in a manner so as to extend outwardly
from a common
vertical shaft 50 of a production well 51, as shown in Fig. 2a. Each of
collector wells 62', 52",
and 52m have apertures 43 therein such as screened slots which resist ingress
of sand but
allow ingress of oil 9 into the collector wells 52', 52", and 52" for
subsequent production to
surface 40 via common vertical shaft portion 50. Advantageously in such
manner, namely by
being able to use a common vertical shaft portion 50 for each of horizontal
collector wells 52',
- 14-
CAL LAIN\ 1865667\1
CA 02794205 2012-11-02
52", and 52", the capital cost of drilling such horizontal collector wells
52', 52", and 52" can
be reduced as compared to the cost of otherwise drilling individual separate
production wells.
Mulit-lateral well drilling techniques are herein defined as a well drilling
technique having
one main wellbore (eg vertical shaft 50 in Fig. 4a), with lateral wellbores
(eg horizontal
collector wells 52', 62", and 521" extending outwardly therefrom. The main
bore or laterals can
be completed in using casing, liner, screens or open hole. Drilling of multi-
lateral wells has been
conducted in the past in oil and gas fields, but not been publicly used or
conceived to the
inventor's knowledge in any patent publication for use in a SAGO application ,
namely for
increasing the number of collector (production) wells in proportion to the
number of injector
wells, nor for that matter while maintaining (as explained in Examples 1A and
!B herein) the total
number of wells constant as compared to a conventional SAGD configuration.
For drilling collector wells 52', 52", and 52'", various levels are suitable
and satisfactory:.
- LEVEL 1 - Open/Unsupported Junction
¨ LEVEL 2 ¨ Main bore Cased & Cemented Lateral Open
¨ LEVEL 3 ¨ Main bore Cased & Cemented. Lateral Cased but not Cemented
Depending on depth and length of the horizontal portion of collector wells
52', 52", and
52", the above "level" employed, and the number of multi-lateral collector
wells, the cost
savings as opposed to drilling multiple separate individual production wells
will vary, but
nonetheless a cost savings will be achieved in most, if not all situations.
Various known methods and apparatus for diverting a drill bit laterally within
a well-bore
for drilling multi-lateral wells extending outwardly therefrom are known.
For example, one such downhole tool apparatus and technique for drilling a
lateral well
outwardly from a vertical well is disclosed in US Patent 4,739,843 assigned to
Amoco
Corporation. Other techniques may involve inserting a whipstock.
- 15-
CAL__LAW\ 1865667\1
CA 02794205 2012-11-02
Many other variations of such tools and techniques for drilling multi-lateral
wells are of
common knowledge to persons of skill in the art, and are known under various
trademarks, such
as SealRiteTm 1, Hook HangerTM 2, and QuickPackTm 3
In order to drill collector wells 52', 52", and 52" in a desired direction and
location,
namely below horizontal portion 31 of injector well 30 and substantially
parallel to each other
and to horizontal portion 31 of injector well 30 and consistently placed a
substantially uniform
distance apart, different guiding tools and methods are available in the prior
art, and are known
to persons of skill in lateral drilling of wells.
Some examples are the Halliburton Company Rotating Magnet Ranging Systems
("RMRS"), the Halliburton Company 3D Rotary Steering System (" 3D-RSS") ,
and/or the
Halliburton Company Magnetic Guidance Tool ("MGT'), with the 3D-RSS system
being the
more accurate and recommended of such three systems.
-Combined Embodiment
Fig. 4A and Fig. 4b show a further modified SAGD configuration 102 and method
of the
present invention combining the advantages of the aforementioned first and
alternative
embodiments of the invention.
Specifically, Fig. 4A shows an embodiment of the invention 102 which combines
the
features and advantages of the alternative embodiment 101 shown in Fig.'s 2a
and 2b, namely
providing a plurality of collector wells 52', 52", and 52" in relation to each
injector well 30, are
combined with the modified configuration and advantages of the first
embodiment shown in Fig.
3, namely having the vertical shaft 50 of the production well 51 drilled at an
opposite end 62 of
the region 10 under development from the end 60 of region 10 at which the
injector well 30 is
drilled.
SealRiteTM is an United States registered trademark of Halliburton Energy
Services Inc. for Multilateral
oil and gas well subsurface completion equipment, namely, latch couplings,
packers, liners, nipples, and
whipstocks
2 Hook HangerTM is an unregistered trademark of Baker Hughes Inc.
QuickPackTm is an unregistered trade-mark of Weatherford Inc.
- 16-
CAL _LAW\ 1865667\1
CA 02794205 2012-11-02
-Further Combined Embodiment
Figs. 5a & Fig. 6b show a further modification to the embodiment 103 of the
invention
shown in Fig. 4a and Fig. 4b, which again takes advantage of the features of
the first
embodiment (production and injector wells drilled from opposite ends of a
region 10), and the
use of multiple collector wells in relation to injector wells, and preferably
further drilling the
multiple collector wells using multi-lateral techniques, with the further
modification that such
concept of drilling multi-lateral wells is extended to the injector wells as
well.
Accordingly, in the further combined configuration and method shown in Figs.
5a & Fig.
5b, a plurality of horizontal portions 31', 31", and 31" in the form of
injector wells are drilled
1.0 and paired with an equal or greater number of horizontal collector
wells 51', 51", 51", 51" and
51".
In such embodiment, multi-lateral collector wells 51', 61", 61", 51i" and 51"
are drilled
laterally outwardly from common vertical shaft 50 using multi-lateral well
drilling techniques as
set out above, and similarly multi-lateral horizontal portions 31', 31", and
31" are drilled
laterally outwardly from vertical shaft 29 of injector well 30.
In a preferred embodiment, namely the embodiment shown in Fig.s 6a and 5b, the
vertical shaft 60 of production well 52 is drilled at an end 62 of development
region 10 opposite
to an end 60 at which the vertical shaft 29 of the injector well 30 is
drilled, to reduce "short-
circuiting" of steam at the heel 7 of each of horizontal injector wells 31',
31", and 31'" into
horizontal collector wells 51', 51", 51", 511" and 51".
-Still Further Embodiment
Fig.'s 10-13 broadly illustrate a further aspect of the present invention,
namely methods
for improving recovery from a an existing already-drilled SAGD well pair
comprising a steam
injector well 30 and a production well 61 combination as shown in an injector
well-producer
well pair 31-51 respectively in Fig. 10. Specifically, in a first embodiment
of such further
aspect, and as may be seen from Fig.10, the method comprises modification to
such prior art
SAGO configuration by :
(i) drilling, at a second opposite end 62 of a region 10 of the formation
under development
proximate a toe portion 8 of the injector well 30, and via a common inclined
or vertical
shaft 50a, at least one further production well 51a having a horizontal
portion 62a
- 17-
CAL LAW\ 1865667\1
CA 02794205 2012-11-02
substantially parallel to said injector well 30 but spaced vertically below
said horizontal
portion 31 of said injector well 30 and extending into the development region
10 as
shown in Fig. 11;
(ii) injecting steam into said injector well 30 and thereby into the region 10
of the formation
under development via said horizontal portion 31 of said injector well 30; and
(iii) collecting within said horizontal portion 52a of said at least one
further production well
61a, heated oil 9 from said formation that has flowed into said horizontal
portion 62a of
said further production well 61a , and producing said oil 9 to surface.
Advantageously, by drilling new production well 51a, the problem of leakage of
steam 9
from the injector well 30 into the heel 7 of the production well 51 is
eliminated, due to the
alignment of high and low pressure areas HP, LP of the injector well 30 with
the corresponding
high and low pressure areas HP, LP respectively of the new production well
51a, leading to
more efficient heating of the region 10, and improved recovery.
Example 2 below provides actual test data establishing the efficacy and
utility of such
method in rejuvenating output from an existing SAGD well.
Figs. 12 & 13 illustrate a further refinement and modification of the above
method to
rejuvenate an existing SAGD well pair comprising an existing injector well 30
and an existing
production well 51, both drilled from one end 60 of a region 10 of a formation
under
development. In such further refinement, instead of drilling a production well
51a at an opposite
end of a formation 10 wherein such production well 61a possesses only one
horizontal portion
52a , in such refined method multi-lateral well drilling techniques as
discussed above are used
to drill a plurality of horizontal collector wells 62a, 62a' extending
outwardly from the vertical
shaft portion 50a of production well 6.1a. In such manner, not only are the
benefits of avoiding
leakage achieved similar to the configuration and method depicted in Fig. 10,
11 achieved, but
further benefits of total production and improved initial recovery are further
achieved due to
the increased ratio of collector wells 52a, 52a' to injector well 30.
EXAMPLE 'IA
In order to establish baseline production data from a prior art SAGD
configuration, a
- 18-
CALLAW\1865667\1
CA 02794205 2012-11-02
traditional prior art SAGD configuration, as shown in Fig. 6 was modelled
using STARS TM 4
computer modelling software, version 2009.1, provided by Computer Modelling
Group Limited
of Calgary Alberta.
Specifically, a hydrocarbon-containing formation
having the typical properties,
temperatures, porosities, permeability, and viscosity of resident bitumen
therein, was assumed
as shown in Table 1 below:
Table 1.
-
31f .................................................. -101141F-t,,,
gtzoikAti'4%;4:
Pay Tkrs rn 25
True Vertical Oeptil (above the sub-sea elevation) ra 1345
Porosity 84
'lame/ 00 Saturation 05
Initial Water Saturation - 15
Gas Mole Nadi an fraction 0.05
Horizorttal Permeability reD 5000
Vertical Permeability mD 4,000
Reservoir Temperature
initial Reservoir Pressure kPa 3,500
,Fiock Compressibility ,j1APsi 7.00E-OS
Thermal Conductivity 2.22E*05
Weil Length SOO
*King of gorizont al in SAGO 100
,
Spacing of Prodrontal legs laterally (for ailL.SAtiCi) 33 S3
,Niumber of Legs
Rod c Heat Capacsty jof 1.39E+06
7witgilitAphuvrolit- :;:gõ
;',t,shat lawitiooktolga
'Molar Density .grnole,em3 3,419
\iisnosity, Dead Oii 141 C 3Z800
Mscoiity in the Stearn Chamber CP 10
:Average firloieculer wept Cif .14\eitt 596
,011 ritiOle Fraction Fraction 0-95
Compressibility 540E417
tarmitifozgisA,
lietWiTirtear
.Steam Rate irri3/ri 400
...,Stearn Quality .05
Producer BP (Minimum) kPa 1,000
µStart-tip duration month 3
Specifically, a series of four (4) steam injector wells 30 , having horizontal
portions 31,
were modelled, spaced a distance of 50 meters apart.
4 Unregistered trade-mark of Computer Modelling Group Limited , of Calgary
Alberta, for software programs
useful for studying behavior of subterranean hydrocarbon containing formations
-19-
CAL LA W\ 1865667\1
CA 02794205 2012-11-02
A corresponding number of respective horizontal portions 52 of production
wells 51 were
modelled a uniform distance of 5 meters below, to create a series of injector-
producer well pairs;
each of said horizontal portions 31 and 62 being modelled of equal length (800
meters as set
out in Table 1 above).
After a start-up duration of 3 months, using a steam injection rate of 400
ma/day
through each of the four(4) injector wells 31 (combined injection rate of 1600
m3/day), the oil
rate production (ms/day) for such prior art SAGD well configuration was
recorded over an
extrapolated period extending approximately eight(8) years from May, 2012 to
August 2020.
Fig. 8 shows a graphical representation of the obtained oil rate production
(ma/day) over
such eight(8) year period, and Fig. 9 shows cumulative oil production over
such eight (8) year
period, with the appropriate line appearing as "SAGD" in both Fig. 8 & Fig. 9.
EXAMPLE 1B
A modified SAGD well configuration was modelled in accordance with one aspect
of the
invention, namely that aspect wherein the number of production (collector)
wells is increased
relative to the number of injector wells, and is shown in Fig. 7.
Specifically, a modified SAGD configuration was chosen, which for comparative
purposes to the prior art SAGD configuration shown in Fig. 6, possessed the
identical number
of wells (albeit altered in ratio, namely six(6) collector wells and two (2)
injector wells 30 ,
whereas the prior art modelled configuration of Fig. 6 possessed four(4)
injector wells 30 wells
and four(4) production wells 51).
Identical formation properties, well length, and oil properties as used in
Example 1A and
as set out in Table 1 above were similarly used in this Example 1B.
Identical steam injection rates (400 ma/day) were injected through the
horizontal portions
31 of each of the two injector wells 30 (only 800 m3/clay combined steam
injection steam rate),
with the horizontal portions of the collector wells 52 being located a similar
distance of 5 meters
below the corresponding horizontal portion 31 of the injector well 30.
An identical lateral span distance of 150 meters was used, identical to the
lateral span
distance of 150 meters used in the standard SAGD model of Fig. 6.
- 20-
CAL _LAW\ 1865667\1
CA 02794205 2012-11-02
After a similar start-up duration of 3 months, using a combined steam
injection rate of
800 m3/day through the two(2) injector wells 31, the oil rate production
(m3/day) for such prior
art SAGD well configuration was recorded over an extrapolated period extending
approximately
eight(8) years from May, 2012 to August 2020.
Fig. 8 shows a graphical representation of the obtained oil rate production
(e/day) over
such eight(8) year period using such configuration, and Fig. 9 shows
cumulative oil production
over such eight (8) year period using such configuration , with the
appropriate line appearing as
"ML-SAGD" in both Fig. 8 & Fig. 9.
As may be seen from a comparison of lines "SAGD" and "ML-SAGD" in each of
Fig.'s 8
& Fig. 9, for the same number of drilled wells, and the identical volume of
hydrocarbon
containing formation under development, the modified SAGD configuration and
method of the
present invention having an increased ratio of production wells to injector
wells resulted in
higher recovery rates and total cumulative production, and used only 1/2 the
amount of steam
injected, thereby representing a real increase in the CSOR.
EXAMPLE 2
An actual SAGD well pair, existing as part of a formation under development in
a Husky
Energy Inc. thermal field ("the Celtic pool") that contained twenty-one (21)
well pairs located
near Lloydminster, Saskatchewan, was used to obtain an understanding of
improvement which
could be achieved by modifying an existing SAGD well pair, whose performance
had diminished
and become non-economical, by drilling a further production well from an
opposite end of the
region under development.
Details of such testing are explained in greater detail in the Canadian
Society for
Unconventional Gas publication SCUG/SPE SPE-149239-PP, authored by Kamran R
Jorshari,
and Brendan O'Hara, each of Husky Energy Inc., and presented at the Canadian
Unconventional Resources Conference held in Calgary, Alberta, Canada, 15-17
November
2011.
By way of summary of salient points, performance of an existing SAGD well pair
in the
Celtic field (Section 17, Township 52, Range 23, west of the 3'd meridian),
having an injector
well 14 and a production well 13, both drilled from the same end of the region
under
- 21-
CALLAW\ 1865667\1
CA 02794205 2012-11-02
development, horizontal sections of each being separated by a distance of 4-6
meters, was
monitored overtime.
Average well properties of the formation in the area under development are set
out in
Table 2, below:
Table 2
10-16
-e
OiHiii1ioia 8.
Oil Oratr (API) 12
1110..*P440,1:4*-
100
. ....
The 13/14 SAGD well pair under study had been in production since Q4 of 2005,
with
other well pairs in the area spaced about 100 meters apart. The channel top
was located at a
depth of approximately 470 meters, in unconsolidated very fine to fine grain
sand with little clay
content. The formation sandpack had excellent porosity and permeability, and
was highly
saturated with heavy oil, as indicated by the 80% saturation percentage set
out in Table 2
above.
The well pair in question began producing in December 2005.
Fig. 14 shows the initial oil rate for the 13/14 well pair, from December
2005. As may be
seen therefrom, oil rate never substantially exceeded 100m3/day for any
extensive period of
time.
Due to low production, in February 2010 a further production well I3A was
drilled from
the opposite end of the region under development, parallel to the existing
well injector 14, but
slightly below existing production well 13.
- 22-
CAL_LAVV\ 1865667\1
CA 02794205 2014-06-19
Weil 13A was initially steamed for a 3 week period to maintain approximately
2,500kPa
reservoir pressure.
Thereafter, production was commenced.
Fig. 15 shows the produced oil rate over time from such modified well pair
13A/ 14.
Importantly, production over time showed a linear increase, and afier
approximately 300
days exceeded 1.00m1/day, approaching 120 m3/day,
The foregoing is considered as illustrative only of the principles of the
invention. Thus,
while certain aspects and embodiments of the invention have been described,
these have been
presented by way of example only and are not intended to limit the scope of
the invention. The
scope of the claims should not be limited by the exemplary embodiments set
forth in the
foregoing, but should be given the broadest interpretation consistent with the
specification as a
whole.
- 23 -
