Note: Descriptions are shown in the official language in which they were submitted.
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Improvements in hydrocarbon production, in particular using gravity drainage
Field of the invention
The present invention relates to the field of hydrocarbon production, in
particular to
methods and apparatus for producing hydrocarbons from the subsurface of the
Earth.
More specifically, the invention in certain embodiments relates to hydrocarbon
reservoirs comprising heavy oil or bitumen and producing hydrocarbons
therefrom by
gravity drainage.
Background
In order to produce hydrocarbons from the Earth's subsurface, wells are
provided that
extend from a well head at the surface into a reservoir region of the
subsurface where
the hydrocarbons have accumulated. Typically, the hydrocarbons are in the form
of
fluid, such as oil or gas, which is able to flow freely under natural pressure
conditions
into and up through the well to the surface.
However, hydrocarbons comprising extra heavy oil or bitumen will not flow
easily using
solely pressure drive, as is the case in many subsurface hydrocarbon
accumulations
around the world. These kinds of hydrocarbons are viscous, sticky substances
that
tend to adhere to the matrix of the rock formation in the subsurface. In order
to
produce such hydrocarbons, it is typically sought to treat the rock formation
in order to
mobilise the hydrocarbons and allow them to flow and be produced through a
well.
There are a number of techniques for mobilising and producing the mobilised
hydrocarbons from the subsurface. Gravity-controlled and thermal processes may
be
favoured, and steam-assisted gravity drainage (SAGD) is one such process that
is
often favoured for bitumen reservoirs.
In SAGD, an injection well ("injector") and a production well ("producer")
cooperate to
mobilise and produce hydrocarbons. The
producer is arranged to produce
hydrocarbons that the injector has served to mobilise. The injector and the
producer
have respective well heads at surface, and wellbores which extend into the
subsurface
and penetrate the reservoir. The wellbores have respective injector and
producer
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sections that are arranged horizontally, with horizontal long axes, in the
reservoir
region. The horizontal injector and producer sections are arranged adjacent to
each
other with the injector section above the producer section. The injector and
producer
sections are typically placed near the bottom of the reservoir. Using the
injector well,
steam is carried into the injector section and injected into the formation.
The injector
section typically has openings along the length of the section to direct steam
radially
out of the injector section and into the surrounding formation. This injection
of steam
generates a high-temperature vapour or steam chamber which heats the
surrounding
bitumen, thus reducing its viscosity and allowing it to drain by gravity into
the producer
section located below. The producer section typically has pathways (e.g.
apertures,
inlets, perforations, flow control devices or the like) along its length,
which may function
to permit and guide flow from the formation radially into the wellbore of the
producer
section. The vapour or steam chamber will be understood to be the region of
the
subsurface rock formations into which steam has penetrated for mobilising
hydrocarbons.
Typically, more than one such set of adjacent injector and producer sections
is used for
drainage, in order to provide "good" coverage and productivity from a given
reservoir.
A problem associated with this is how to do this efficiently, and maximise
recovery. In
particular, as injection of steam progresses, the vapour and/or steam from
each injector
section rises such that the chambers grow upwards vertically and laterally.
Eventually,
the steam chambers from the injector sections merge together and coalesce, and
hydrocarbons are mobilised in the region between adjacent injector-producer
sets. A
particular challenge is to place and operate wells appropriately to extract
the
hydrocarbons mobilised in this way. It is recognised that simply applying
multiple sets
of injectors and producers as described above across the reservoir region may
not be
sufficient, or may be prohibitively expensive, and thus uneconomic. The
practice of
drilling an additional well from the surface between such sets at later stages
of
production can reportedly increase production and improve recovery
performance, but
is similarly not without significant upfront cost. A suggestion for how such
wells may be
configured for the production of hydrocarbons in a gravity drainage process is
described in the patent publication US7556099 (EnCana). The patent publication
US2012/0285700 (Imperial) describes a technique whereby a region containing
accumulations of unrecovered hydrocarbons is identified, and a well is then
drilled and
used to extract hydrocarbons from the identified region.
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Summary of the invention
It is recognised that the practice of drilling additional wells in late stages
of the
production process, once steam has been injected, can suffer a risk of
intersection with
the active steam chamber while drilling. Multiple penetrations of the
reservoir cap rock
by wells can adversely affect the structure of the cap rock and the conditions
in and
around the reservoir. In addition, larger well pads or well pad expansion may
be
required to accommodate additional wells to ensure sufficient spacing between
the
wellheads of each SAGD injector-producer set and the well head of any
additional well,
so as to allow for accessibility around the wellheads during and after
drilling and
completion activities. However, expansion and installation of equipment at the
well pad
can be costly.
In light of the above, in a first aspect of the invention, there is provided
apparatus for
producing hydrocarbons from the Earth's subsurface, comprising: at least one
injector
well section arranged to be provided in the subsurface for injecting a fluid
for mobilising
the hydrocarbons; and a first multilateral well section arranged to be
provided in the
subsurface adjacent to the injector well section for producing the mobilised
hydrocarbons.
The apparatus may further comprise a second multilateral well section arranged
to be
provided in the subsurface. The second multilateral well section may have
multiple
uses, for example it may have different functions in different parts of a
production
process. In certain embodiments, the second section may be configured to
produce
the mobilised hydrocarbons. The second multilateral well section may be
provided with
inflow apparatus to let mobilised hydrocarbons flow into the section to
produce the
hydrocarbons. In certain embodiments, the second section may be configured to
stimulate the subsurface to facilitate mobilising the hydrocarbons. The second
multilateral well section may be provided with injection apparatus, e.g.
nozzles, radial
pathways, or tubing perforations in a liner, to inject a fluid to stimulate
the subsurface.
In certain embodiments, the second multilateral well section may be configured
to
perform observations of the subsurface. The second multilateral well section
may
have measurement apparatus, e.g. sensors, such as temperature or pressure
sensors
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or the like, installed to perform measurements of subsurface properties for
performing
the observations.
The first multilateral well section may be provided with inflow apparatus to
let mobilised
hydrocarbons flow into the first section. The inflow apparatus may comprise
one or
more of: an inflow control device; a sand screen; a production liner; and a
production
packer.
The injector well section may be provided with outflow apparatus to inject the
fluid flow
out of the injector section and into the subsurface. The outflow apparatus
comprises
one or more of: an outflow control device; and injection well tubing. The
outflow
apparatus may comprise a nozzle, pathway, or the like for fluid from an
injection tubing
into the subsurface.
The second multilateral well section may be arranged to be coupled to the
first
multilateral well section at a joining location below the cap rock of a
reservoir of the
hydrocarbons in the subsurface.
The second multilateral well section may be arranged to be provided in the
subsurface
along a horizontal direction and in spaced apart parallel relationship with
the first
section. The apparatus may be adapted for producing hydrocarbons by gravity
drainage.
According to a second aspect of the invention, there is provided a method of
producing
hydrocarbons from the Earth's subsurface, comprising: (a) injecting a fluid
through at
least one injector well section into the subsurface to mobilise the
hydrocarbons; and (b)
using a first multilateral well section to produce the mobilised hydrocarbons,
the first
multilateral well section being provided adjacent to the injector well
section.
The method may further comprise using a second multilateral well section. The
second
multilateral well section is preferably coupled to the first multilateral well
section below
a hydrocarbon reservoir cap rock. The second multilateral well section is
typically also
used to produce the hydrocarbons.
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The method may further comprise, prior to using the second multilateral well
section to
produce the hydrocarbons, measuring at least one property of the subsurface
using the
second multilateral well section.
5 The method may further comprise using the measured property to determine
a location
for a flow control device along a production tubing string, and providing the
production
tubing string in the second multilateral well section to use the second
multilateral well
section to produce the hydrocarbons.
The method may further comprise drilling the borehole of the second
multilateral well
section prior to said step of injecting the fluid.
The fluid injected may comprise any one or more of: vapour; steam; solvent;
non-
condensable gas; and mixtures thereof. The subsurface may comprises oil sands.
The hydrocarbons comprise any one or more of: oil; heavy oil; extra heavy oil;
and
bitumen. The method may be a method for producing hydrocarbons by gravity
drainage.
According to a third aspect of the invention, there is provided a
multilateral, first well
comprising a producer section arranged to be provided adjacent to an injector
section
of a second well, to produce hydrocarbons which are mobilised by injection of
a fluid
into the subsurface via the injector section.
According to a fourth aspect of the invention there is provided a method of
constructing
the multilateral first well of the third aspect.
According to a fifth aspect of the invention there is provided apparatus for
producing
hydrocarbons from the Earth's subsurface, comprising: a section of a first
well for
injecting a fluid into the subsurface to mobilise the hydrocarbons; and a
section of a
multilateral second well being arranged adjacent to the injector section, for
producing
the mobilised hydrocarbons.
According to a sixth aspect of the invention there is provided a method of
producing
hydrocarbons from the Earth's subsurface, comprising: injecting a fluid into
the
subsurface through a section of a first well to mobilise the hydrocarbons; and
producing
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the mobilised hydrocarbons through a section of a multilateral second well
which is
arranged adjacent to said section of the first well.
According to a seventh aspect of the invention there is provided apparatus for
producing hydrocarbons from the Earth's subsurface, comprising: a first well
comprising a section arranged to be provided in the subsurface for injecting a
fluid for
mobilising the hydrocarbons; and a multilateral, second well comprising a
section
arranged to be provided in the subsurface adjacent to the injector section for
producing
the mobilised hydrocarbons.
According to an eighth aspect of the invention there is provided a method of
producing
hydrocarbons from the Earth's subsurface, comprising: (a) injecting a fluid
through at
least one section of a first well into the subsurface to mobilise the
hydrocarbons; and
(b) using a section of a multilateral, second well to produce the mobilised
hydrocarbons, the section of the second well being provided adjacent to said
section of
the second well.
According to a ninth aspect of the invention there is provided apparatus for
producing
hydrocarbons from the Earth's subsurface, comprising: at least one injector
section for
injecting a fluid into the subsurface to mobilise the hydrocarbons; and a
producer
section of a multilateral well for producing the mobilised hydrocarbons, the
producer
section being arranged adjacent to the injector section.
According to a tenth aspect of the invention there is provided a method of
producing
hydrocarbons from the Earth's subsurface, comprising: injecting a fluid into
the
subsurface through at least one injector section to mobilise the hydrocarbons;
and
using a producer section of a multilateral well to produce the mobilised
hydrocarbons,
the producer section being arranged adjacent to the injector section.
According to an eleventh aspect of the invention, there is provided apparatus
for
producing hydrocarbons from the Earth's subsurface, comprising: a first well
set
comprising a first injector section and a first producer section arranged
adjacent to the
first injector section; a second set comprising a second injector and a second
producer
section arranged adjacent to the second injector section, the first and second
injector
sections being arranged to inject a fluid into the subsurface to mobilise the
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hydrocarbons, and the first and second producer sections being arranged to
produce
the mobilised hydrocarbons; and a third producer section arranged between the
first
and second sets and coupled to either of the first and second producer
sections.
The third producer section may be arranged to extend horizontally and in
parallel with
either or both of the first and second producer sections in the subsurface.
The third
producer section may be arranged to produce hydrocarbons mobilised by either
or both
of the injected fluid from the first injector and the second injector section,
in a region
between the injector sections. The third producer section may be arranged
midway
between the first and second producer sections. The third producer section may
be
arranged at the same depth within the subsurface of either of the first and
second
producer sections.
The third producer section may be operable to perform observations of the
subsurface
when not being operated to produce hydrocarbons. The third producer may be
coupled to either of the first or second producer section at a joining region
below the
hydrocarbon reservoir cap rock. The third producer and the first or second
producer
section to which the third producer may be coupled may be connected to a
common
trunk section for connecting the coupled producer sections with a surface
facility.
According to a twelfth aspect of the invention there is provided a method of
providing
the apparatus of any of the first, fifth, seventh, ninth or eleventh aspects
of the
invention.
Any of the above aspects may have further features as defined in relation to
any of the
other aspects. Any of the aspects may have further features as described
elsewhere
herein, in particular in the description, drawings and claims.
Features that are
described as part of one example embodiment may be used in other embodiments
where they are compatible with the other features in the other embodiment.
Description
There will now be described, by way of example only, embodiments of the
invention
with reference to the accompanying drawings, in which:
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Figure 1 is a schematic perspective representation of apparatus according to
an
embodiment of the invention;
Figure 2 is an end-on cross-sectional representation of injector and producer
sections
arranged in a subsurface reservoir in a process of producing hydrocarbons from
the
reservoir, according to an embodiment of the invention;
Figure 3 is an end-on cross-sectional representation of injector and producer
sections
arranged in a subsurface reservoir in a process of producing hydrocarbons from
a
subsurface reservoir;
Figure 4A is a representation of a multilateral well in a first configuration;
Figure 4B is a cross-sectional representation of the multilateral well of
Figure 4A along
the line A-A;
Figure 4C is a cross-sectional representation of the multilateral well of
Figure 4B along
the line B-B;
Figure 4D is a cross-sectional representation of the multilateral well of
Figure 4B along
the line C-C; and
Figure 5 is a cross-sectional representation of the multilateral well of
Figure 4A in a
second configuration.
With reference firstly to Figure 1, there is shown schematically apparatus 1
for use in
producing hydrocarbons, such as heavy oil or bitumen, from a reservoir in the
subsurface by using a gravity controlled drainage process, which for purposes
of the
examples below is SAGD.
The apparatus 1 has a first well 2 and a second well in the form of a
multilateral well 3.
The first well 2 has a section, in the form of an "injector section" 5, for
injecting a fluid
into the subsurface. The section 5 has a generally horizontal trajectory in
the
subsurface. The multilateral well 3 comprises, at its downhole end, first and
second
sections 7,9 that are laterally offset with respect to one another in the
subsurface
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reservoir by a distance B in the y-direction. These sections 7,9 can be termed
"laterals" or lateral sections of the multilateral well. The laterals extend
along different
lateral paths in the subsurface, in the x-direction. As seen in the figure,
the first and
second sections 7,9 are also arranged generally in parallel with each other.
Long axes
of the wellbores of the sections 7, 9 are horizontal and extend in the x-
direction.
The first section 7 of the multilateral well is arranged adjacent to the
injector section 5.
In addition, the first lateral section 7 is arranged directly below the
injector section 5,
and generally in parallel thereto, being separated by a distance A in the
vertical (depth)
z-direction.
In order to produce hydrocarbons, a mobilising injection fluid in the form of
steam is
injected into the subsurface formation through the injector section 5. The
injected
steam mobilises the heavy oil or bitumen in the reservoir, in a so-called
steam chamber
or mobilised zone of the reservoir. The heavy oil or bitumen is then able to
flow with
condensed water from the injected steam substantially under the control of
gravity to
the first and second sections 7,9 where the mobilised hydrocarbons flow into
the
sections 7,9. In this way, the hydrocarbons are collected and produced from
the
subsurface using the producer section provided by the multilateral well. The
first lateral
section 7 and the injector section 5 may be considered, respectively, as
producer and
injector sections as described in the background section above, except that
the
producer section 7 is provided in a multilateral well.
Typically, the second section 9 is operated to produce hydrocarbons at later
stages of
production from the reservoir, when the steam chamber established by the
injector
section 5 has developed a significant distance laterally, and hydrocarbons are
mobilised that are not extractable via the first lateral section 7. Prior
to this, the
second section 9 is typically not used or not needed to produce hydrocarbons,
and
hydrocarbons are produced solely via the first section 7 of the multilateral
well.
The distance A can be up to 15 m, preferably between 2 to 10 m, and more
preferably
around 5 m as is typical for SAGD-based production. The distance B may for
example
be in the region of 20 to 100 m, but is typically around 50 m, although this
can depend
upon properties of the reservoir.
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With reference next to Figure 2, the process of producing hydrocarbons using
the
apparatus of Figure 1 is explained in further detail. At an early stage of
production from
the reservoir 200, steam is injected into the subsurface reservoir using the
injector
section 5. The elevated temperature of the steam heats, softens and/or reduces
the
5 viscosity of the extra heavy oil or bitumen, so that hydrocarbons are
mobilised and can
flow, allowing them to be produced. The injector section is used to generate a
steam
chamber to provide a mobilised hydrocarbon zone 202. The steam chamber is in
effect
a convective cell. At the cooler extremities of the cell, mobilised oil and
condensed
water are carried in downward convective flow, driven by gravity as indicated
by arrows
10 in Figure 2 whilst steam is injected into the reservoir from the
injector section 5. The
figure shows a stage of production, where mobilised hydrocarbons are being
produced
through both the first and second sections 7,9 of the multilateral well 3. The
first and
second sections are therefore both acting as "producer sections" to produce
hydrocarbons from the subsurface reservoir. It can be noted that at an earlier
stage in
the process, mobilised hydrocarbons may be produced solely through the first
lateral
section 7, whilst the second section 9 of the well is not active to produce
hydrocarbons.
This may be the case where hydrocarbons in the vicinity of the second section
are not
mobilised sufficiently so as to be able to be produced through the second
section 9.
The steam chamber may not have grown laterally far enough to do so
effectively. As
will be described below, the second section 9 can be put to a different use if
not being
used actively to produce hydrocarbons. It can also be noted that the second
section 9,
at earlier stages of the process, may not yet have been formed. This depends
on
requirements.
In Figure 3, an embodiment is depicted in which the second section 9 of the
multilateral
well is not being used to produce hydrocarbons. This will normally be in an
earlier
stage of the process than the situation of Figure 2. Instead, it is being used
in an
"injection mode" as a second injector section through which steam is injected
to help
mobilize the hydrocarbons in the reservoir. This can help to accelerate the
formation
and growth of a steam chamber and increase the region of mobilized
hydrocarbons.
After a period of time, the use of the second section 9 can be switched to
production
mode so that it is used to produce the mobilized hydrocarbons. The
multilateral well
may thus be operated to switch the second section 9 to production mode, e.g.,
when it
is determined that the steam chamber has developed sufficiently that effective
production is feasible.
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With further reference now to Figures 4A to 4D, an example of a multilateral
well 40 is
described, as may be used in the apparatus and processes described above. The
well
40 has first and second sections 41, 42 comprising respective horizontal
boreholes
completed and fitted with a perforated liner 41s, 42s for receiving mobilized
hydrocarbons therethrough from the surrounding subsurface. The first and
second
sections are coupled. They join together at a junction in a joining region 43
below the
cap rock 50 in the subsurface. The sections connect to a common trunk section
45
that connects the lateral sections 41, 42 to the surface. In this way, as can
be seen,
the sections are laterally spaced apart from each other at the downhole end,
in the
reservoir, and join together at an uphole location, in the joining region. The
multilateral
well thus branches or splays from one wellbore at the surface (e.g. at the
well head)
into two wellbore sections 41, 42 further downhole, in the subsurface.
Produced fluids
including hydrocarbons from the first and second lateral sections 41, 42 are
received
and combined in the trunk section as indicated by arrows 46 and conveyed to
the
surface therethrough. A pump 47 is arranged in the trunk section 45 acting on
the
combined fluid to lift the fluids to the surface (not shown) through the
production tubing
51 inside the trunk section 45 to remove the hydrocarbons from the well. The
junction
of the two sections must either have a level of sand control that is
comparable to the
production liner, or it may be provided open hole where the formation is
competent.
The pump 47 is placed in its own tangent section above the junction. The
tangent
section is preferably a long straight section in the trunk section 45
typically of around
50 m in length. The pump can then be kept straight making it less prone to
failure.
Figures 4C and 40 show the opening 48a to which the end 48b of the second
section
42 is connected to the first section 41 and trunk section 45.
As exemplified in Figure 4A, by way of the multilateral well, production can
take place
through both the first and second lateral sections 7,9 of Figure 1, or
sections 41, 42 of
Figure 4A, with a common producer well head and well pump serving both
sections,
e.g. at the stage of process such as described in relation to Figure 3.
In Figure 5, a variant on the arrangement of Figures 4A to 4D is exemplified,
whereby
the multilateral well is operated to put the second lateral section 42 to a
different use
than production, whilst production continues through the first section 41
(e.g. as in
Figure 3 above). The second lateral section 42 in this example is configured
to
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stimulate the reservoir while the first lateral section 41 of the multilateral
well is
producing fluids (the second section 42 is not producing fluids). A tubing
string 52 is
run into the opening into lateral section 42 and is hydraulically isolated
from the
producing first section 41 with a packer 53. The tubing string 52 provides the
ability to
stimulate the reservoir near the lateral section 42 using a combination of
injection fluids
including steam, water, or solvent. In another variant, the tubing 52 may
extend further
into the opening and into the lateral section 42, and the reservoir may be
stimulated
using electrical heaters run inside the tubing and into the horizontal section
of the
lateral section 42. In a further option, with the lateral section 42 isolated
hydraulically, it
can be pressurized with an injection fluid to create a pressure drive of
production fluids
in the horizontal direction from the lateral towards the first section 41
being used as a
producer. This will accelerate production of mobilized fluids at the lower
part of the
reservoir by supplementing gravity drive with pressure drive.
The first and second wells can be formed using established well construction
techniques. The construction of the wells involves drilling suitable boreholes
into the
earth along defined trajectories and providing a suitably completed injector
section and
completed lateral sections of the multilateral well in the reservoir, for
example as
described above. A first borehole is for example drilled from the surface to
provide the
horizontal first section 41 of the multilateral producer. A second borehole is
then drilled
from the surface following along the trajectory of the first, but spaced
vertically apart
therefrom, to provide the injector section of the first well vertically above
the first
section 41 of the multilateral well. The first borehole is then re-entered and
a third, side
track borehole is drilled into the wall of the first borehole at an
appropriate point there
along for creating the second section 42 of the multilateral well. The entry
point for
drilling of the side track borehole is preferably selected to be below the
reservoir cap
rock. As such, the junction 43 is provided below the cap rock. This means that
only
the trunk section 45 pierces the cap rock, and it is not necessary to drill
two holes
through the cap rock in order to provide two lateral sections in the reservoir
of the
subsurface. This helps to minimize disturbances to the cap rock and helps to
maintain
cap rock integrity.
The multilateral well is fitted with suitable completion equipment in the
boreholes of the
first and second lateral sections for producing hydrocarbons as described
above.
When producing through two or more lateral sections of the multilateral well,
a common
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production pump is inserted in the common trunk section, above the point of
entry of
the side track. Preferably, the drilling of the third borehole for the second
lateral
section of the producer is performed "cold", i.e. before the formation is
heated
significantly by injection of steam via the injector; however, it could be
drilled at a later
time when the well is "warm", once the formation is heated by the injected
steam. This
could be beneficial if for instance the reservoir conditions indicate that a
different than
expected placement of the second lateral section is required.
Hence, in some embodiments, the side-track borehole is not drilled at the
outset. In
this case, the first stage of the production process may be performed without
the
second section of the producer altogether. When the development of the steam
chambers and mobilisation of hydrocarbons has developed further, the second
section
may be drilled, by re-entering the first borehole, and drilling the side track
borehole
below the cap rock. Drilling cold however reduces the risk of intersection an
active
steam chamber.
In certain examples, rather than performing injection, the second section 9 is
used to
perform observations in the reservoir prior to it being used to receive and
produce
hydrocarbons. This would in effect be a variant on Figure 4. For example, the
lateral
section 9 may be provided with observation equipment such as temperature or
pressure sensors or other sensors for taking measurements of pressure,
temperature
or other parameters, monitoring or otherwise observing conditions in the
subsurface.
Thereafter, such observation equipment may be removed and production equipment
installed such as sand screens, liners, production packers, flow control
devices and the
like for switching over to production mode. Provision of an observation
section in this
manner allows for a better understanding of the initial producer well flow and
the steam
chamber growth in the initial stage of production taking place via the first
lateral section
7. The observations can assist in determining where best to place steam
distribution
devices or inflow control devices in the injector 5, and/or the first and
second sections
7,9 of the multilateral well. For example, in the initial stage of production
as depicted in
Figure 3, the second section 9 may be used as an "observation section" to
obtain
observational data from the reservoir.
In an enhanced oil recovery process, there is the potential for injection
fluids to enter
the production well. This is normally controlled by adjusting the rate of
production from
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14
the producer well using the artificial lift system (e.g., pump). If a
situation arises where
injection fluids begin to enter the production well, the pump will be slowed
to decrease
the amount of production fluid being removed from the reservoir. Other
strategies can
be employed to prevent the breakthrough of injection fluids. This includes
installing flow
control devices with a flow resistance that is pre-set according to predicted
variations in
reservoir geology or according to variations in well position (i.e., depth
position or
lateral position), with both factors predisposing certain sections of the well
to
breakthrough of injection fluids.
In the use of the multilateral well of the present invention to produce
hydrocarbons, the
approach can be similar. The artificial lift system remains important for
maximizing the
rate of production fluid removed from the well, while avoiding the
breakthrough of
injection fluids from occurring. Another method is to install permanent flow
control
devices on the pipes of the producer sections according to predicted
geological
variations and well position. The second section of the multilateral well is
typically
constructed from pipes that are 12-14 m long. Permanent flow control devices
can be
installed on each pipe segment, such that production rates of fluid entering
the well
sections can be managed at over 12-14 m increments by choosing flow control
devices
setting. Another strategy is to install non-permanent flow control devices on
a tubing
string that is run inside the producer section. A benefit of the observations
from the
second section of the well is that such measurements can be used for the
sizing and
positioning of non-permanent flow control devices installed on the tubing
string.
In the multilateral well, the single pump can operate both producer sections
simultaneously. Since the lateral sections of the producer are connected by
the
junction, pressure communication between the laterals is nearly instantaneous.
This
allows bottomhole pressures in both lateral producer sections of the well to
be adjusted
quickly by well operating personnel for the purpose of maximizing production
while
avoiding injection fluids from entering the producer sections.
In practice, it is desirable to provide for multiple sets of adjacent injector
and producer
sections in a reservoir region in order to perform SAGD and maximise the
production
from the region.
CA 02847898 2014-03-31
In other embodiments, the multilateral well may have three or more subsurface
lateral
sections, not just two as described above. One of the lateral sections would
then be
used adjacent to and provided beneath the injector as a producer section to
optimally
collect mobilised hydrocarbons at the base of the steam chamber.
5
Further, in other embodiments, a fluid other than steam may be injected for
mobilising
the hydrocarbons. Such a fluid preferably heats the hydrocarbons. The fluid
may
comprise any one or more of: a solvent, steam mixed with a solvent, or a non-
condensable gas, such as methane or the like.
Costs associated with expansion of surface facilities, and costs of adding
well heads
and pump equipment inside wells, in order to reach new regions of the
reservoir can be
reduced through the use of a multilateral well as described herein. The
current concept
means that two horizontal producer sections can be tied to a single wellhead,
a single
build section, and a single pump, which can help to reduce costs compared with
prior
art techniques. The costs of implementation with a multilateral well providing
a
producer section will be the same as for a single well (non-multilateral) SAGD
producer, except for that of adding the second horizontal section and packer
to allow
the added section to be opened and used for production when it is needed. Risk
is
reduced, as the second section can conveniently be drilled cold, at the stage
of
constructing the first section, rather than at a later stage when the steam
chamber has
developed. In summary, the invention is generally targeted at reducing well
costs,
while also reducing the risk of drilling near an active steam chamber.
Various modifications and improvements may be made without departing from the
scope of the invention herein described.
