Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVING RECOVERY FROM A HYDROCARBON RESERVOIR I/
FIELD
[0001] The present techniques relate to harvesting resources using
gravity
drainage processes. Specifically, techniques are disclosed for placing holes
in the
bottom of wells within a reservoir.
BACKGROUND
[0002] This section is intended to introduce various aspects of the
art, which
may be associated with exemplary embodiments of the present techniques. This
discussion is believed to assist in providing a framework to facilitate a
better
understanding of particular aspects of the present techniques. Accordingly, it
should
be understood that this section should be read in this light, and not
necessarily as
admissions of prior art.
[0003] Modern society is greatly dependant on the use of hydrocarbons
for
fuels and chemical feedstocks. Hydrocarbons are generally found in subsurface
rock formations that can be termed "reservoirs." Removing hydrocarbons from
the
reservoirs depends on numerous physical properties of the rock formations,
such as
the permeability of the rock containing the hydrocarbons, the ability of the
hydrocarbons to flow through the rock formations, and the proportion of
hydrocarbons present, among others.
[0004] Easily harvested sources of hydrocarbon are dwindling, leaving
less
accessible sources to satisfy future energy needs. However, as the costs of
hydrocarbons increase, these less accessible sources become more economically
attractive. For example, the harvesting of oil sands to remove hydrocarbons
has
become more extensive as it has become more economical. The hydrocarbons
harvested from these reservoirs may have relatively high viscosities, for
example,
ranging from 8 API, or lower, up to 20 API, or higher. Accordingly, the
hydrocarbons
may include heavy oils, bitumen, or other carbonaceous materials, collectively
referred to herein as "heavy oil," which are difficult to recover using
standard
techniques.
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[0005] Several methods
have been developed to remove hydrocarbons from
oil sands. For example, strip or surface mining may be performed to access the
oil
sands, which can then be treated with hot water or steam to extract the oil.
However, deeper formations may not be accessible using a strip mining
approach.
For these formations, a well can be drilled to the reservoir and steam, hot
air,
solvents, or combinations thereof, can be injected to release the
hydrocarbons. The
released hydrocarbons may then be collected by the injection well or by other
wells
and brought to the surface.
[0006] A number of
techniques have been developed for harvesting heavy oil
from subsurface formations using thermal recovery techniques. Thermal recovery
operations are used around the world to recover liquid hydrocarbons from both
sandstone and carbonate reservoirs. These operations include a suite of steam
based in situ thermal recovery techniques, such as cyclic steam stimulation
(CSS),
steam flooding, and steam assisted gravity drainage (SAGO).
[0007] For example, CSS
techniques includes a number of enhanced
recovery methods for harvesting heavy oil from formations that use steam heat
to
lower the viscosity of the heavy oil. The steam is injected into the reservoir
through
a well and raises the temperature of the heavy oil during a heat soak phase,
lowering
the viscosity of the heavy oil. The same well may then be used to produce
heavy oil
from the formation. CSS is generally practiced in vertical wells, but systems
are
operational in horizontal wells. CSS and other steam flood techniques have
been
utilized worldwide, beginning in about 1956 with the utilization of CSS in the
Mene
Grande field in Venezuela and steam flood in the early 1960s in the Kern River
field
in California.
[0008] Solvents may be
used in combination with steam in CSS processes,
such as in mixtures with the steam or in alternate injections between steam
injections. These techniques are described in U.S. Patent No. 4,280,559 to
Best,
U.S. Patent No. 4,519,454 to McMillen, and U.S. Patent No. 4,697,642 to Vogel,
among others.
[0009] Another group of
techniques is based on a continuous injection of
steam through a first well to lower the viscosity of heavy oils and a
continuous
production of the heavy oil from a lower-lying second well. Such techniques
may be
termed "steam assisted gravity drainage" or SAGD. Various embodiments of the
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SAGO process are described in Canadian Patent No. 1,304,287 to Butler and its
corresponding U.S. Patent No. 4,344,485.
[0010] In SAGD, two horizontal wells are completed into the reservoir.
The
two wells are first drilled vertically to different depths within the
reservoir. Thereafter,
using directional drilling technology, the two wells are extended in the
horizontal
direction that result in two horizontal wells, vertically spaced from, but
otherwise
vertically aligned with the other. Ideally, the production well is located
above the
base of the reservoir but as close as practical to the bottom of the
reservoir, and the
injection well is located vertically 10 to 30 feet (3 to 10 meters) above the
horizontal
well used for production.
[0011] Each of the wellbores is assembled from pipe segments, for
example,
of about 30 feet in length. Each pipe segment has exterior threads at one end
and
interior threads at the opposite end that couple the segments together.
Variations in
the threading can result in slight variations of the orientation of each
segment to the
.. next segment in the string.
[0012] The upper horizontal well is utilized as an injection well and
is supplied
with steam from the surface. The steam rises from the injection well,
permeating the
reservoir to form a vapor chamber that grows over time towards the top of the
reservoir, thereby increasing the temperature within the reservoir. The steam,
and
its condensate, raise the temperature of the reservoir and consequently reduce
the
viscosity of the heavy oil in the reservoir. The heavy oil and condensed steam
will
then drain downward through the reservoir under the action of gravity and may
flow
into the lower production well, whereby these liquids can be pumped to the
surface.
At the surface of the well, the condensed steam and heavy oil are separated,
and the
heavy oil may be diluted with appropriate light hydrocarbons for transport by
pipeline.
[0013] Solvents may be used alone or in combination with steam
addition to
increase the efficiency of the steam in removing the heavy oils. As the
solvents
blend with the heavy oils and bitumens, they lower the viscosity, allowing the
materials to flow towards a production well. The mobility of the heavy oil
obtained
with the steam and solvent combination is greater than that obtained using
steam
alone under substantially similar formation conditions.
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[0014] The techniques discussed above may have uneven or even limited
injection of steam into the reservoir, for example, due to the random
orientation of
the pipe segments to each other in the reservoir. Further, conventional
slotted liners,
meshrite, and wirewrap screen assemblies have openings that allow fluids to
flow
into the liner from 360 degrees. With these liners in SAGD, steam coning will
occur
when the steam chamber is proximal to top of the liners. This can lead to
lower
efficiency for steam injection as well as early steam breakthrough.
SUMMARY
[0015] Some embodiments of the present invention provide variations of
method for improving recovery from a subsurface hydrocarbon reservoir. The
method includes drilling a well with a horizontal segment through a reservoir
interval,
installing a pipe string having a plurality of screen assemblies in the
horizontal well
segment, locating each of the plurality of screen assemblies, and drilling a
hole in the
pipe string at a portion of the plurality of screen assemblies, wherein each
hole is
drilled at a desired orientation to a radial axis of the drill string.
[0016] Other embodiments of the invention include variations of a
system for
improving the recovery of resources from a reservoir. The system includes a
reservoir, a horizontal well drilled through the reservoir, wherein the
horizontal well
comprises a plurality of pipe joints that have a screen assembly mounted
thereon; a
detection apparatus configured to locate a screen assembly on a pipe joint;
and a
drilling device configured to drill a hole in a pipe joint at a selected
orientation to the
vertical.
[0017] Yet other embodiments of the invention include variations of a
method
for harvesting hydrocarbons from an oil sands reservoir. The method includes:
drilling a steam assisted gravity drainage (SAGD) well pair through the oil
sands
reservoir; placing a pipe string in each of the wells of the SAGD well pair,
wherein
the pipe string comprises a plurality of screen assemblies, and wherein the
pipe
string has no holes prior to placement; selecting a portion of the screen
assemblies
at which to drill holes in a base pipe underneath the screen assembly;
drilling the
holes at a selected orientation to the radial axis of the base pipe; injecting
steam into
an injection well in the SAGD well pair; and producing fluids from a
production well in
the SAGD well pair.
4
[0017a] Certain exemplary embodiments can provide a method for
improving
recovery from a subsurface hydrocarbon reservoir, comprising: drilling a well
comprising
a horizontal segment through a reservoir interval; installing a pipe string in
the horizontal
segment, wherein the pipe string comprises a plurality of screen assemblies;
locating
each of the plurality of screen assemblies; drilling at least one hole in the
pipe string at a
portion of the plurality of screen assemblies, wherein each hole is drilled at
a desired
orientation to a radial axis of the pipe string; identifying from the at least
one hole, that
has failed in one of the plurality of screen assemblies; plugging the failed
hole; and
drilling a new hole.
[0017b] Certain exemplary embodiments can provide a method for harvesting
hydrocarbons from an oil sands reservoir, comprising: drilling a steam
assisted gravity
drainage (SAGD) well pair through the oil sands reservoir; placing a pipe
string in each
of the wells of the SAGD well pair, wherein the pipe string comprises a
plurality of
screen assemblies, and wherein the pipe string has no holes prior to
placement;
selecting a portion of the screen assemblies at which to drill holes in a base
pipe
underneath the screen assembly; drilling the holes at a selected orientation
to a radial
axis of the base pipe; injecting steam into an injection well in the SAGD well
pair;
producing fluids from a production well in the SAGD well pair; identifying one
of the
plurality of screen assemblies that has failed; determining the reason for the
failure, if
the failure is due to a hole failing: drilling a new hole under the one of the
plurality of
screen assemblies; and if the failure is due to the screen assembly failing:
plugging the
hole under the one of the plurality of screen assemblies; and drilling a new
hole under a
new one of the plurality of screen assemblies.
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DESCRIPTION OF THE DRAWINGS
[0018] The advantages of the present techniques are better understood
by
referring to the following detailed description and the attached drawings, in
which:
[0019] Fig. 1 is a drawing of a steam assisted gravity drainage (SAGD)
.. process used for harvesting hydrocarbons in a reservoir;
[0020] Fig. 2 is a drawing of a screen assembly, showing a location of
a hole;
[0021] Fig. 3 is a cross section of a blast joint section of the
screen assembly
of Fig. 2;
[0022] Fig. 4 is a cross section of a wirewrap screen section of the
screen
.. assembly of Fig. 2;
[0023] Fig. 5 is a drawing of a pipe segment that includes a wirewrap
screen;
[0024] Fig. 6 is a drawing of a pipe segment, showing a build-up in
condensate due to non-vertical hole locations;
[0025] Fig. 7 is a drawing of a pipe segment, showing complete
drainage of
.. condensate when the holes are located at the bottom of a segment;
[0026] Fig. 8 is a plot showing the use of gamma ray logging to locate
blast
joints to allow the positioning of holes;
[0027] Fig. 9(A) is a drawing of a series of screen assemblies placed
on a
pipe segment;
[0028] Fig. 9(B) is a drawing of a series of screen assemblies placed on a
pipe segment;
[0029] Fig. 9(C) is a drawing of a series of screen assemblies placed
on a
pipe segment; and
[0030] Fig. 10 is a method of improving the harvesting of hydrocarbons
from a
.. reservoir by drillings holes after the well is lined.
DETAILED DESCRIPTION
[0031] In the following detailed description section, specific
embodiments of
the present techniques are described. However, to the extent that the
following
description is specific to a particular embodiment or a particular use of the
present
techniques, this is intended to be for exemplary purposes only and simply
provides a
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description of the exemplary embodiments. Accordingly, the techniques are not
limited to the specific embodiments described below, but rather, include all
alternatives, modifications, and equivalents falling within the true spirit
and scope of
the appended claims.
[0032] At the outset, for ease of reference, certain terms used in this
application and their meanings as used in this context are set forth. To the
extent a
term used herein is not defined below, it should be given the broadest
definition
persons in the pertinent art have given that term as reflected in at least one
printed
publication or issued patent. Further, the present techniques are not limited
by the
usage of the terms shown below, as all equivalents, synonyms, new
developments,
and terms or techniques that serve the same or a similar purpose are
considered to
be within the scope of the present claims.
[0033] As used herein, the term "base" indicates a lower boundary of
the
resources in a reservoir that are practically recoverable, by a gravity-
assisted
drainage technique, for example, using an injected mobilizing fluid, such as
steam,
solvents, hot water, gas, and the like. The base may be considered a lower
boundary of the payzone. The lower boundary may be an impermeable rock layer,
including, for example, granite, limestone, sandstone, shale, and the like.
The lower
boundary may also include layers that, while not completely impermeable,
impede
the formation of fluid communication between a well on one side and a well on
the
other side.
[0034] "Bitumen" is a naturally occurring heavy oil material.
Generally, it is the
hydrocarbon component found in oil sands. Bitumen can vary in composition
depending upon the degree of loss of more volatile components. It can vary
from a
very viscous, tar-like, semi-solid material to solid forms. The hydrocarbon
types
found in bitumen can include aliphatics, aromatics, resins, and asphaltenes. A
typical bitumen might be composed of:
19 wt. % aliphatics (which can range from 5 wt. %-30 wt %, or higher);
19 wt. % asphaltenes (which can range from 5 wt. %-30 wt. %, or higher);
30 wt. % aromatics (which can range from 15 wt. %-50 wt. A), or higher);
32 wt. % resins (which can range from 15 wt. %-50 wt. %, or higher); and
some amount of sulfur (which can range in excess of 7 wt. %).
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In addition bitumen can contain some water and nitrogen compounds ranging from
less than 0.4 wt. `)/0 to in excess of 0.7 wt. %. The percentage of the
hydrocarbon
types found in bitumen can vary. As used herein, the term "heavy oil" includes
bitumen, as well as lighter materials that may be found in a sand or carbonate
reservoir.
[0035] As used herein, two locations in a reservoir are in "fluid
communication" when a path for fluid flow exists between the locations. For
example, the establish of fluid communication between a lower-lying serpentine
well
and a higher injection well may allow material mobilized from a steam chamber
above the injection well to flow down to the serpentine well from collection
and
production. As used herein, a fluid includes a gas or a liquid and may
include, for
example, a produced hydrocarbon, an injected mobilizing fluid, or water, among
other materials.
[0036] As used herein, a "cyclic recovery process" uses an
intermittent
injection of injected mobilizing fluid selected to lower the viscosity of
heavy oil in a
hydrocarbon reservoir. The injected mobilizing fluid may include steam,
solvents,
gas, water, or any combinations thereof. After a soak period, intended to
allow the
injected material to interact with the heavy oil in the reservoir, the
material in the
reservoir, including the mobilized heavy oil and some portion of the
mobilizing agent
may be harvested from the reservoir. Cyclic recovery processes use multiple
recovery mechanisms, in addition to gravity drainage, early in the life of the
process.
The significance of these additional recovery mechanisms, for example dilation
and
compaction, solution gas drive, water flashing, and the like, declines as the
recovery
process matures. Practically speaking, gravity drainage is the dominant
recovery
mechanism in all mature thermal, thermal-solvent and solvent based recovery
processes used to develop heavy oil and bitumen deposits, such as steam
assisted
gravity drainage (SAGD). For this reason the approaches disclosed here are
equally
applicable to all recovery processes in which at the current stage of
depletion gravity
drainage is the dominant recovery mechanism.
[0037] "Facility" as used in this description is a tangible piece of
physical
equipment through which hydrocarbon fluids are either produced from a
reservoir or
injected into a reservoir, or equipment which can be used to control
production or
completion operations. In its broadest sense, the term facility is applied to
any
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equipment that may be present along the flow path between a reservoir and its
delivery outlets.
Facilities may comprise production wells, injection wells, well
tubulars, wellhead equipment, gathering lines, manifolds, pumps, compressors,
separators, surface flow lines, steam generation plants, processing plants,
and
delivery outlets. In some instances, the term "surface facility" is used to
distinguish
those facilities other than wells.
[0038] "Heavy
oil" includes oils which are classified by the American
Petroleum Institute (API), as heavy oils, extra heavy oils, or bitumens. In
general, a
heavy oil has an API gravity between 22.3 (density of 920 kg/m3 or 0.920
g/cm3)
and 10.00 (density of 1,000 kg/m3 or 1 g/cm3). An extra heavy oil, in general,
has an
API gravity of less than 10.0' (density greater than 1,000 kg/m3 or greater
than 1
g/cm3). For example, a source of heavy oil includes oil sand or bituminous
sand,
which is a combination of clay, sand, water, and bitumen. The thermal recovery
of
heavy oils is based on the viscosity decrease of fluids with increasing
temperature or
solvent concentration. Once the viscosity is reduced, the mobilization of
fluids by
steam, hot water flooding, or gravity is possible. The reduced viscosity makes
the
drainage quicker and therefore directly contributes to the recovery rate.
[0039] A
"hydrocarbon" is an organic compound that primarily includes the
elements hydrogen and carbon, although nitrogen, sulfur, oxygen, metals, or
any
number of other elements may be present in small amounts. As used herein,
hydrocarbons generally refer to components found in heavy oil, or other oil
sands.
[0040] As used
herein, "poorer quality facies" are intervals in a reservoir that
can have poor drainage, often due to a difficulty in establishing a counter-
current
flow. In an oil sands reservoir, poorer quality facies may include IHS layers
above
the higher quality sands of a clean pay interval.
[0041]
"Permeability" is the capacity of a rock to transmit fluids through the
interconnected pore spaces of the rock. The customary unit of measurement for
permeability is the millidarcy. The term "relatively permeable" is defined,
with
respect to formations or portions thereof, as an average permeability of 10
millidarcy
or more (for example, 10 or 100 millidarcy). The term "relatively low
permeability" is
defined, with respect to formations or portions thereof, as an average
permeability of
less than about 10 millidarcy.
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[0042] "Pressure" is the force exerted per unit area by the gas on the
walls of
the volume. Pressure can be shown as pounds per square inch (psi).
"Atmospheric
pressure" refers to the local pressure of the air. "Absolute pressure" (psia)
refers to
the sum of the atmospheric pressure (14.7 psia at standard conditions) plus
the
gauge pressure (psig). "Gauge pressure" (psig) refers to the pressure measured
by
a gauge, which indicates only the pressure exceeding the local atmospheric
pressure (i.e., a gauge pressure of 0 psig corresponds to an absolute pressure
of
14.7 psia). The term "vapor pressure" has the usual thermodynamic meaning. For
a
pure component in an enclosed system at a given pressure, the component vapor
pressure is essentially equal to the total pressure in the system.
[0043] As used herein, a "reservoir" is a subsurface rock or sand
formation
from which a production fluid, or resource, can be harvested. The rock
formation
may include sand, granite, silica, carbonates, clays, and organic matter, such
as
bitumen, heavy oil, oil, gas, or coal, among others. Reservoirs can vary in
thickness
from less than one foot (0.3048 m) to hundreds of feet (hundreds of m). The
resource is generally a hydrocarbon, such as a heavy oil impregnated into a
sand
bed.
[0044] As discussed in detail above, "Steam Assisted Gravity Drainage"
(SAGD), is a thermal recovery process in which steam, or combinations of steam
and solvents, is injected into a first well to lower a viscosity of a heavy
oil, and fluids
are recovered from a second well. Both wells are generally horizontal in the
formation and the first well lies above the second well. Accordingly, the
reduced
viscosity heavy oil flows down to the second well under the force of gravity,
although
pressure differential may provide some driving force in various applications.
Although SAGD is used as an exemplary process herein, it can be understood
that
the techniques described can include any gravity driven process, such as those
based on steam, solvents, or any combinations thereof.
[0045] "Substantial" when used in reference to a quantity or amount of
a
material, or a specific characteristic thereof, refers to an amount that is
sufficient to
provide an effect that the material or characteristic was intended to provide.
The
exact degree of deviation allowable may in some cases depend on the specific
context.
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[0046] As used herein, "thermal recovery processes" include any type
of
hydrocarbon recovery process that uses a heat source to enhance the recovery,
for
example, by lowering the viscosity of a hydrocarbon. These processes may use
injected mobilizing fluids, such as hot water, wet steam, dry steam, or
solvents
alone, or in any combinations, to lower the viscosity of the hydrocarbon. Such
processes may include subsurface processes, such as cyclic steam stimulation
(CSS), cyclic solvent stimulation, steam flooding, solvent injection, and
SAGD,
among others, and processes that use surface processing for the recovery, such
as
sub-surface mining and surface mining. Any of the processes referred to
herein,
such as SAGD, may be used in concert with solvents.
[0047] A "wellbore" is a hole in the subsurface made by drilling or
inserting a
conduit into the subsurface. A wellbore may have a substantially circular
cross
section or any other cross-sectional shape, such as an oval, a square, a
rectangle, a
triangle, or other regular or irregular shapes. As used herein, the term
"well," when
referring to an opening in the formation, may be used interchangeably with the
term
"wellbore." Further, multiple pipes may be inserted into a single wellbore,
for
example, as a liner configured to allow flow from an outer chamber to an inner
chamber.
Overview
[0048] Current throttle-flow liner designs often use screen assemblies on
pipe
segments, such as wirewrap screens, wirewrap screens with blast joints, and
the
like, to improve the contact of wellbores with a reservoir. As used herein, a
liner is a
portion of a well used for recovering resources from a reservoir. The liner
may often
have a base pipe with attached screen assemblies for allowing fluid flow into
and out
of the base pipe. Before installation, a limited number of holes may be
drilled in the
base pipe, behind the screen assemblies, to regulate the flow to or from the
reservoir.
[0049] In an embodiment, the screen assemblies are located and the
holes
are drilled after the screen assemblies have been installed in the reservoir.
This
allows the holes to be positioned at any selected angle to the radial axes of
horizontal pipe segments. For example, the holes can be positioned to point
downward into the screen assembly. A low position, combined with a "V shape"
drainage profile, can reduce the quantity of injectant vapor, such as steam,
solvent
vapor, or combinations, than may be coned into a production well, e.g., being
produced as
vapor. By reducing the liquid sump above the depth of the producer, it can
also increase
the height of the pay interval that is exposed to the injectant vapor, further
increasing the
production rates and recovery.
[0050] For the purposes of this description, SAGD is used as the recovery
process.
Those ordinarily skilled in the art will recognize that the approaches
disclosed here are
equally applicable to all thermal, thermal-solvent and solvent based recovery
processes in
which gravity drainage is the dominant recovery mechanism.
[0051] Fig. 1 is a drawing of a steam assisted gravity drainage (SAGD)
process 100
used for accessing hydrocarbon resources in a reservoir 102. In the SAGD
process 100,
steam 104 can be injected through injection wells 106 to the reservoir 102. As
previously
noted, the injection wells 106 may be horizontally drilled through the
reservoir 102.
Production wells 108 may be drilled horizontally through the reservoir 102,
with a production
well 108 underlying each injection well 106. Generally, the injection wells
106 and
production wells 108 will be drilled from the same pads 110 at the surface
112. This may
make it easier for the production well 108 to track the injection well 106.
However, in some
embodiments the wells 106 and 108 may be drilled from different pads 110.
[0052] The injection of steam 104 into the injection wells 106 may result
in the
mobilization of hydrocarbons 114 in the reservoir 102, which may drain to the
production
wells 108 and be removed to the surface 112 in a mixed stream 116 that can
contain
hydrocarbons, condensate and other materials, such as water, gases, and the
like. As
described herein, screen assemblies may be used on the injection wells 106,
for example,
to throttle the inflow of injectant vapor to the reservoir 102. Similarly,
screen assemblies
may be used on the production wells 108, for example, to decrease sand
entrainment.
[0053] The hydrocarbons 114 may form a triangular shaped drainage chamber
118 that
has the production well 108 at located at a lower apex 124. The mixed stream
116 from a
number of production wells 108 may be combined and sent to a processing
facility 120. At
the processing facility 120, a mixture of 122 of water and hydrocarbons can be
separated,
and the mixture 122 of water and hydrocarbons sent on for further refining.
Water from the
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separation may be recycled to a steam generation unit within the facility 120,
with or without
further treatment, and used to generate the steam 104 used for the SAGD
process 100.
[0054] An interval of the reservoir 102 may include poorer quality
facies, such as an IHS
layer, which drains poorly. The poorer quality fades are not limited to
intervals at the top of
a reservoir 102, but may include lenses or other places in the reservoir 102.
As described
herein, cycling the pressure of the reservoir 102 may increase the drainage
from the interval
and lenses, allowing increases in production of hydrocarbons from these
locations.
Screen Assemblies
[0055] Fig. 2 is a drawing 200 of a screen assembly 202 mounted on a base
pipe 204.
.. In this example, a center section of the screen assembly 202 has a blast
joint 206, which is
joined to wirewrap screens 208 along each outer edge of the blast joint 206.
The wirewrap
screens 208 are joined to the base pipe 204 by welds 210, for example, to
prevent injectant
from escaping around the wirewrap screens 208 or sand from infiltrating
beneath the
wirewrap screens 208. A hole 212 is drilled below the blast joint 206 to allow
injectant
.. vapor to escape from injection wellbores or production fluids to enter
production wellbores.
[0056] A design criterion for conventional liners, such as slotted
liners, wirewrap
screens, or meshrite screens, is to ensure that sufficient open area is
present in the to
prevent the liner from being a flow restriction. However, this design approach
can make the
screens of the liners susceptible to sand influx damage such as erosion or
plugging. For
example, this may occur if high fluid velocities are present at one or more
locations along a
wellbore.
[0057] Fig. 3 is a cross section of the blast joint 206 of the screen assembly
202 of Fig.
2. The blast joint 206 is a single metal pipe, for example, made from iron or
steel, The hole
212 in the base pipe 204 opens behind the blast joint 206. In this example,
the hole 212 is
oriented along the vertical axis 304 of the base pipe. In an injection well,
the injectant, such
as steam, is released into the annulus 302 between the blast joint 206 and the
base pipe
204. This protects the more fragile wirewrap screens 208 from erosion
caused by the influx of injectant vapor. The injectant vapor flows through
the annulus 302 to the wirewrap screens 208, as discussed with respect to
Fig. 4. Further, the presence of the blast joints 206 directly outside the
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locations of the holes 212 will deflect the injectant vapor exiting the holes,
thereby
ensuring that it will not adversely affect the operation of any underlying
production
well.
[0058] Fig. 4 is a cross section of a wirewrap screen 208 of the
screen
assembly 202 of Fig. 2. For a production well, the injectant vapor that exits
the base
pipe 204 through the hole 212 into the annulus 302 between the base pipe 204
and
the blast joint 206 flows to the annulus 402 between the wirewrap screens 208
and
the base pipe 204. From there, the injectant vapor flows into the reservoir
through
slots in the wirewrap screen 208. Similarly, for a production well, production
fluids
can flow through the slots in the wirewrap screen 208 into the annulus 402
between
the wirewrap screens 208 and the base pipe 204 and then into the annulus 302
between the base pipe 204 and the blast joint 206. The production fluids can
then
flow into the base pipe 204 of the production well through the hole 212.
[0059] The throttled-flow liner design for the screen assembly 202,
illustrated
in Figs. 2-4, can improve the robustness of the screen assembly 202 to damage
by
creating a flow restriction in a base pipe 204, for example, by limiting the
number of
holes 212. In contrast, previous systems had the flow restriction occur across
the
wirewrap screen 208. When the throttled flow liner is the screen assembly 202
used
for injection wells, the number of screen assemblies 202 and their specific
locations
along the wellbore are based on the requirements of the specific thermal,
thermal-
solvent or solvent based recovery process. However, the orientation of the
holes
212 for each of the segment a string of pipe is random and, thus, may not be
optimal
in all services, as discussed with respect to Fig. 5.
[0060] Fig. 5 is a drawing of a pipe segment (or joint) 502 that
includes a
screen assembly 202 and a pre-drilled hole 504. The pipe segment 502 has male
threads 506 at one end and female threads 508 at the opposite end. The pipe
segment 502 is installed into the formation as a part of a pipe string that is
formed by
joining pipe segments 502 in an end-to-end configuration in which the male
threads
506 of each pipe segment 502 are joined to the female threads 508 of the next
pipe
segment. Depending on the reservoir, every pipe segment 502 may have a screen
assembly 202. In some embodiments, blank joints, which are pipe segments with
no
screen assembly 202, may be inserted into the pipe string. The orientation of
each
predrilled hole 504 is then determined by the orientation of the pipe segment
502
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when the threads are completely joined to the next pipe segment. Thus, the
predrilled holes 504 may be somewhat randomly oriented to the vertical axis of
the
pipe segment 502, which may lower the flow through the pipe.
[0061] Fig. 6 is a drawing of a pipe string 600, showing a build-up of
liquid 602
that can result when the holes 604 are not located at the bottom of the pipe
string
600. The level 606 of the liquid 602 is controlled by the distance of the
holes 604
from the bottom of the vertical axis 608. In this example, the holes 604 are
located
about half way up from the bottom of the pipe string 600 and, as a result, the
lower
half of the pipe string 600 is filled with liquid 602, effectively reducing
the cross-
sectional area available for vapor flow 610 by about 50%. This can result in a
substantial pressure drop. Fig. 6 illustrates that liquid 602, or other
fluids, can
accumulate in the injector wellbore when using a design with a restricted
number of
holes 604 that are drilled prior to the pipe string 600 being installed, such
as is the
case with a throttled-flow liner design.
[0062] Fig. 7 is a drawing of a pipe string 700, showing complete drainage
of
condensate when the holes are located at the bottom of the pipe string 700. In
an
embodiment, the pipe string 700 is installed without pre-drilling holes behind
the
screen assemblies. After installation, the locations of the screen assemblies
202 can
be determined. For example, blast joints 206 that may be integral to each
screen
assembly 202 can be found using various techniques, as discussed further with
respect to Fig. 8. The holes 702 can then be drilled in the pipe string 700
behind the
screen assemblies 202, allowing the holes 702 to be drilled substantially
downwards
with respect to the radial axis 704 of the pipe string 700.
[0063] In addition to lowering the amount of liquid that may build up
in an
injection well, the downward orientation of the holes 702 makes production
wells
more resistant to the coning of vapor, which causes reproduction of the vapor
from
the production wells. As the production of steam or other vapors can be a
significant
operating cost for thermal enhanced oil recovery (EOR) operations, preventing
vapor
reproduction can improve the project economics.
[0064] Fig. 8 is a plot 800 showing the use of gamma ray logging to locate
blast joints to allow the positioning of holes. The x-axis 802 represents the
distance
down the wellbore from the surface location (in meters), while the y-axis 804
represents the intensity 806 of gamma rays received at a detector. As the
gamma
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ray logging is measuring gamma rays emitted by natural sources in the
surrounding
=
rock, a lower value can represent a higher density for the surrounding pipe.
The
gamma logging tool can identify the increased density of the blast joints
located
above the base pipe. Each of the low points can then be used to identify a
location
for drilling a hole 808.
[0065] In embodiments, any number of other techniques may be
used to
locate screen assemblies for drilling the holes. For example, a thicker wall
section of
pipe can be installed at a known offset from each screen assembly for location
by
the gamma ray logging. Portions of the ring or base pipe itself can be tagged,
such
as with a radioactive source, allowing the accurate positioning of the tool
for drilling
each hole. Further, a weak radioactive tag may be directly included at each
location,
for example, in a blast joint, to accurately locate the tool for the drilling
of each hole.
[0066] In an embodiment, a profiled section of the base pipe,
for example,
about 0.5 to 1 cm narrower than the base pipe, may be included in proximity to
the
planned hole location to locate the tool. Similarly, a profile section may be
included
in the segment that provides an indentation for an accurately positioning of
the tool
for the drilling of each hole. To move past the indentation, the tool can be
rotated to
disengage the indentation and then moved. A segmented ring may be included to
function in a similar manner. The segmented ring can engage the tool at one
orientation and disengage when the tool is rotated to a different orientation.
[0067] Once the locations are determined, specialized drilling
tools can be
used to drill the required number of holes with the desired locations and
orientations.
For example, such tools can include the MaxPERF Drilling Tool, available from
Penetrators Canada, Inc. of Red Deer, Alberta, Canada. For injection wells,
the
preferred hole orientation is vertically downward as this can help to ensure
that any
liquids present, such as condensate, can be easily removed from the pipe
string. As
discussed previously, if the hole orientation allowed these liquids to
accumulate
within the liner, the liquids would effectively reduce the hydraulic diameter
of the
liner, increasing the pressure drop along the injection liner. In some
instances, the
holes may be slightly offset from the vertical axis at the bottom of the pipe.
For
example, this may be done in a production well to provide a sump for sand that
infiltrates the well bore. Not all of the screen assemblies have to be placed
into
production at the time of installation as discussed with respect to Figs. 9(A)-
(C).
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Sparing Screen Assemblies
[0068] Fig.
9(A) is a drawing of five installed screen assemblies 202 placed on
a pipe string 900. Spare screen assemblies 202, for example, which are not
opened
to flow immediately after installation, can be installed during the initial
installation of
the pipe string 900. Accordingly, if one or more of the initial screen
assemblies 202
fail, or if a determination is made to change the distribution of steam or
solvent along
the pipe string 900, the holes leading to some screen assemblies 202 can be
obstructed and holes may be drilled at one or more of the spare screen
assemblies
202. As a result, the pipe string 900 can be refurbished at a significantly
lower cost
than redrilling either the horizontal section or the entire well.
[0069] Fig.
9(B) is a drawing of the five installed screen assemblies 202 on the
pipe string 900, in which three of the screen assemblies 202, labeled A, C,
and E,
have been accessed by drilling holes 902. Two remaining screen assemblies 202,
B
and D have been left closed as spares for futures use. As the field matures,
it may
.. be found that some of the screen assemblies 202 have failed, for example,
allowing
sand to accumulate in the pipe string 900 of a production well or to have
become
intervals of excess steam communication in an injection well. The
screen
assemblies 202 involved can be identified by surveying the well for sand
accumulations or intervals of reduced sub-cooling.
[0070] Fig. 9(C) is a drawing of the series of screen assemblies 202 placed
on
a pipe segment, showing the plugging of a hole 904 and drilling of a new hole
906.
In this example, screen assembly 202 C was blocked and a hole 906 was opened
behind screen assembly 202 B to replace screen assembly 202 C. The hole 904 in
the failed screen assembly 202 C can be obstructed, for example, using a
cement
squeeze, a scab liner, or any number of other techniques.
[0071] In
addition to repairing failed screen assemblies 202, as the recovery
process matures, it may become valuable to change the openings to screen
assemblies 200 along either the injection or production wells. The same
techniques
described herein can be used to locate and drill additional holes 908 at a
desired
subset of the open screen assemblies 200. Using these techniques, a well can
be
effectively repaired and rejuvenated for less cost than it would cost to drill
a
replacement well.
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[0072] Fig. 10 is a method of improving the harvesting of hydrocarbons
from a
reservoir by drillings holes after the well is lined. The method 1000 begins
at block
1002 with a mapping of the locations of resources in a reservoir and a plan
for
harvesting those resources. The mapping can include locating positions for
injection
wells and production wells, as well as locating initial and subsequent
positions for
screen assemblies. Generally, the mapping will be performed in the initial
planning
stages of the recovery scheme. For example, prior to the start of recovery
operations, a geologic model can be created for the development area. This
geologic model is usually constructed using a geologic modeling software
program.
Available open hole and cased hole log, core, 2D and 3D seismic data, and
knowledge of the depositional environment setting can all be used in the
construction
the geologic model. The geologic model and knowledge of surface access
constraints can then be used to complete the layout of the recovery process
wells,
e.g., the injection and production wells, and the surface pads.
[0073] At block 1004, a series of performance predictions can be made using
a reservoir simulation program, such as Computer Modeling Group's STARs
program, in order to identify useful locations to open screen assemblies. The
simulations can also help identify how the screen assembly locations should be
changed, for example, by plugging old screen assemblies or drilling holes at
new
screen assemblies, as the field matures.
[0074] The process needs to consider both the needs of individual well
pairs
and the overall pattern needs. For example, changes in geology and well design
may
result in different approaches for different wells within the development. It
may also
be possible to use simple empirical or analog based models for performance
predictions. Further, in many developments, one or more follow-up recovery
processes, such as the drilling of in-fill wells, can be used to further
enhance the
recovery of the hydrocarbons. The options to extend recovery can be considered
during the pressure cycling planning phase, in addition to any operating
pressure
and production rate limitations associated with the installed lift system to
be used in
the production wells.
[0075] At block 1006, the wells, such as SAGD well pairs, used to
harvest the
hydrocarbon from the reservoir can be drilled. After the well pairs have been
drilled,
data collected during their drilling as well as data collected during the
operation of
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the recovery process, such as cased hole logs including temperature logs,
observation wells, additional time lapse seismic or other remote surveying
data, can
be used to update the geologic model. This may be used to map the evolution of
the
depletion patterns as the recovery process matures. The depletion patterns
within
the reservoir will be influenced by well placement decisions, geological
heterogeneity, well failures, and day to day operating decisions. The
depletion
patterns may determine the optimum locations to open new screen assemblies.
[0076] At
block 1008, the holes may be drilled behind the screen assemblies
that are to be initially opened. At block 1010, hydrocarbon resources can be
harvested from the reservoir using the wells. For example, steam, solvent, or
combinations of these agents can be injected into the reservoir through the
open
screen assemblies along the injections wells. Fluids
including hydrocarbons,
injectants, water, and the like, can be produced from the production well
through the
open screen assemblies along the production well.
[0077] At block
1012, a determination can be made as to whether any screen
assemblies have failed. This may also mark the point in production that
planned
changes in the open or closed screen assemblies can be made. If any screen
assemblies have failed or changes are planned, process flow may proceed to
block
1014.
[0078] At block
1014, any holes into screen assemblies that have failed, or
desired to be closed, may be blocked. This may not be needed, if the change is
determined to merely be drilling a new hole under a blast joint in the same
screen
assembly. At block 1016, new holes may be drilled in pipe strings, for
example, at
locations under new screen assemblies and under currently open screen
assemblies
that need increases in flow. Process flow can then return to block 1010 to
continue
production until another screen assembly fails.
[0079] While
the present techniques may be susceptible to various
modifications and alternative forms, the embodiments discussed above have been
shown only by way of example. However, it should again be understood that the
techniques is not intended to be limited to the particular embodiments
disclosed
herein. Indeed, the present techniques include all alternatives,
modifications, and
equivalents falling within the true spirit and scope of the appended claims.
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