Note: Descriptions are shown in the official language in which they were submitted.
CA 02483803 2004-12-02
ATTORNEY DOCKET NO.: UTILITY PATENT
22.1540
(WSM: 30572-PO12US)
WELL TREATMENT SYSTEM AND METHOD
FIELD OF THE INVENTION
[0001] The present invention relates to improving reservoir communication with
a wellbore.
BACKGROUND
[0002] To complete a well, one or more formation zones adjacent a wellbore are
perforated to
allow fluid from the formation zones to flow into the well for production to
the surface or to
allow injection fluids to be applied into the formation zones. A perforating
gun string may be
lowered into the well and the guns fired to create openings in casing and to
extend perforations
into the surrounding formation.
[0003] The explosive nature of the formation of perforation tunnels shatters
sand grains of the
formation. A layer of "shock damaged region" having a permeability lower than
that of the
virgin formation matrix may be formed around each perforation tunnel. The
process may also
generate a tunnel full of rock debris mixed in with the perforator charge
debris. The extent of the
damage, and the amount of loose debris in the tunnel, may be dictated by a
variety of factors
including formation properties, explosive charge properties, pressure
conditions, fluid properties,
and so forth. The shock damaged region and loose debris in the perforation
tunnels may impair
the productivity of production wells or the injectivity of injector wells.
[0004] One popular method of obtaining clean perforations is underbalanced
perforating. The
perforation is carried out with a lower wellbore pressure than the formation
pressure. The
pressure equalization is achieved by fluid flow from the formation and into
the wellbore. This
fluid flow carries some of the damaging rock particles. However, underbalance
perforating may
not always be effective and may be expensive and unsafe to implement in
certain downhole
conditions.
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[0005] Fracturing of the formation to bypass the damaged and plugged
perforation may be
another option. However, fracturing is a relatively expensive operation.
Moreover, clean,
undamaged perforations are required for low fracture initiation pressure and
superior zonal
coverage (pre-conditions for a good fracturing job). Acidizing, another widely
used method for
removing perforation damage, is not effective (because of diversion) for
treating a large number
of perforation tunnels.
[0006] A need thus continues to exist for a method and apparatus to improve
fluid
communication with reservoirs in formations of a well.
SUMMARY OF THE INVENTION
[0007] In view of the foregoing and other considerations, the present
invention relates to treating
a well.
[0008] Accordingly, a well treatment system and method is provided. A well
treatment system
of the present invention includes a housing forming a sealed surge chamber,
and a surge charge
disposed within the sealed surge chamber, wherein the surge charge is adapted
upon activation to
penetrate the housing and to not penetrate material exterior of the housing.
Fluid communication
is created between the surge chamber and the wellbore when the housing is
penetrated by the
surge charge. The penetration permits wellbore fluid to flow quickly into the
surge chamber.
Fluid flow into the surge chamber may enhance a surge of flow from the
formation into the
wellbore.
[0009] The system may further include perforating charges or be combined with
a perforating
gun for perforating the surrounding formation and the casing. It may also be
desired to provide a
well treatment fluid in the wellbore before perforating the formation.
[0010] A well treatment method of the present invention includes the steps of
disposing a
housing having a sealed surge chamber within the wellbore; and detonating a
surge charge,
disposed in the surge chamber, to penetrate the housing thereby providing
fluid communication
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between the surge chamber and exterior of the housing. The surge charge is
adapted to penetrate the housing and not to penetrate the formation, casing or
other
material exterior of the housing.
According to another aspect of the invention, there is provided a tool
string for achieving a transient underbalance condition in a wellbore, the
tool string
comprising: a housing forming a sealed surge chamber; a surge charge disposed
within the sealed surge chamber, wherein the surge charge is adapted upon
activation to penetrate the housing and to not penetrate material exterior of
the
housing; and a chamber carrying a treatment fluid.
According to a further aspect of the invention, there is provided a tool
string for well treatment, the tool string comprising: a housing forming a
sealed surge
chamber wherein a pressure within the surge chamber is less than a pressure
exterior of the housing when the surge chamber is sealed; a surge charge
disposed
within the sealed surge chamber, wherein the surge charge is adapted upon
activation to penetrate the housing and to not penetrate material exterior of
the
housing; a thin walled section formed in the housing adjacent an explosive
cavity of
the surge charge; an explosive perforating charge adapted for penetrating a
material
exterior of the housing; and a chamber carrying a treatment fluid.
According to a still further aspect of the invention, there is provided a
method for treating a well, the method comprising the steps of: placing a tool
string in
a wellbore proximate a formation to be treated comprising a housing having a
sealed
surge chamber, a surge charge disposed within the sealed surge chamber, a
perforating charge, and a chamber carrying a treatment fluid; releasing the
treatment
fluid into the wellbore; detonating the perforating charge to create a tunnel
in the
formation; and detonating the surge charge to penetrate the housing thereby
providing fluid communication between the wellbore and the surge chamber.
According to yet another aspect of the invention, there is provided a
downhole explosive charge adapted to perforate a surge chamber without
damaging
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objects external of the surge chamber to achieve a transient underbalance
condition
in a wellbore, the charge comprising: an explosive having a charge cavity:
wherein
the charge cavity has a substantially infinite radius.
According to still another aspect of the invention, there is provided a
downhole explosive charge adapted to perforate a surge chamber without
damaging
objects external of the surge chamber to achieve a transient underbalance
condition
in a wellbore, the charge comprising: an explosive having a charge cavity:
wherein
the charge cavity has an infinite radius.
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[0011] The foregoing has outlined the features and technical advantages of the
present invention
in order that the detailed description of the invention that follows may be
better understood.
Additional features and advantages of the invention will be described
hereinafter which form the
subject of the claims of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The foregoing and other features and aspects of the present invention
will be best
understood with reference to the following detailed description of a specific
embodiment of the
invention, when read in conjunction with the accompanying drawings, wherein:
[0013] Figure 1 is an illustration of a well treatment system of the present
invention;
[0014] Figure 1A is a cross-sectional view of the surge tool of Figure 1
[0015] Figure 2 is a top, cross-sectional view of a surge tool;
[0016] Figure 3 is a top, cross-sectional view of another surge tool;
[0017] Figure 4 is an illustration of another well treatment system of the
present invention;
[0018] Figure 5 is a flow diagram of a method according to an embodiment of
the present
invention; and
[0019] Figure 6-10 are timing charts of pressure over time pursuant to methods
of the present
invention.
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DETAILED DESCRIPTION
[0020] Refer now to the drawings wherein depicted elements are not necessarily
shown to scale
and wherein like or similar elements are designated by the same reference
numeral through the
several views.
[0021.] As used herein, the terms "up" and "down"; "upper" and "lower"; and
other like terms
indicating relative positions to a given point or element are utilized to more
clearly describe
some elements of the embodiments of the invention. Commonly, these terms
relate to a
reference point as the surface from which drilling operations are initiated as
being the top point
and the total depth of the well being the lowest point.
[0022] Methods and apparatus are provided to treat perforation damage and to
remove debris
from tunnels created by perforation into a well formation. Additional methods
and apparatus are
provided in U.S. Patent No. 7,182,138, U.S. Patent No. 6,732,798 and U.S.
Patent No. 6,598,682.
[0023] There are several potential mechanisms of damage to formation
productivity and
injectivity due to perforation damage. One may be the presence of a layer of
low permeability
sand grains (grains that are fractured by the shaped charge) after
perforation. As the produced
fluid from the formation may have to pass through this lower permeability
zone, a higher than
desired pressure drop may occur resulting in lower productivity. Underbalance
perforating is
one way of reducing this type of damage. However, in many cases, insufficient
underbalance
may result in only partial alleviation of the damage. The second major type of
damage may arise
from loose perforation-generated rock and charge debris that fills the
perforation tunnels. Not all
the particles may be removed into the wellbore during underbalance
perforation, and these in
turn may cause declines in productivity and injectivity (for example, during
gravel packing,
injection, and so forth). Yet another type of damage occurs from partial
opening of perforations.
Dissimilar grain size distribution can cause some of these perforations to be
plugged (due to
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22.1540
(WSM: 30572-PO12US)
bridging, at the casing/cement portion of the perforation tunnel), which may
lead to loss of
productivity and injectivity.
[0024] To remedy these types of damage, two forces acting simultaneously may
be needed, one
to free the particles from forces that hold them in place and another to
transport them. The
fractured sand grains in the perforation tunnel walls may be held in place by
rock cementation,
whereas the loose rock and sand particles and charge debris in the tunnel may
be held in place by
weak electrostatic forces. Sufficient fluid flow velocity is required to
transport the particles into
the wellbore.
[0025] According to various embodiments of the invention, a combination of
events are
provided to enhance the treatment of damage and removal of debris: (1)
application of treatment
fluid(s) into tunnels; and/or (2) creation of a local transient low pressure
condition (local
transient underbalance) in a wellbore interval.
[0026] Examples of treatment fluids that are applied include acid, chelant,
solvent, surfactant,
brine, oil, and so forth. The application of the treatment fluids causes at
least one of the
following to be performed: (1) remove surface tension within perforation
tunnels, (2) reduce
viscosity in heavy oil conditions, (3) enhance transport of debris such as
sand, (4) clean out
residual skin in a perforation tunnel, (5) achieve near-wellbore stimulation,
(6) perform dynamic
diversion of acid such that the amount of acid injected into each perforation
tunnel is
substantially the same, and (7) dissolve some minerals. Basically, application
of the treatment
fluids changes the chemistry of fluids in a target wellbore interval to
perform at least one of the
above tasks. The application of treatment fluids to perforation tunnels is
done in an overbalance
condition (wellbore pressure is greater than formation pressure). Application
of treatment fluids
may be performed by use of an applicator tool, described further below.
[0027] A subsequent fluid surge creates the dynamic underbalance condition
(wellbore pressure
is less than formation pressure) wherein fluid flows from the formation into
the wellbore.
Following the dynamic underbalance condition, the target wellbore interval is
set to any of an
underbalance condition, overbalance condition, and balanced condition. Thus,
according to
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22.1540
(WSM: 30572-PO12US)
some embodiments, a sequence of some combination of overbalance, underbalance,
and
balanced conditions is generated in the target wellbore interval, such as
overbalance-
underbalance-overbalance, overbalance-underbalance-underbalance, overbalance-
underbalance-
balanced, underbalance-overbalance-underbalance, and so forth. This sequence
of different
pressure conditions occurs within a short period of time, such as in a time
period that is less than
or equal to about 10 seconds.
[0028] The local transient underbalance condition is created by use of a surge
chamber
containing a relatively low fluid pressure. For example, the surge chamber is
a sealed chamber
containing a gas or other fluid at a lower pressure than the surrounding
wellbore environment.
As a result, when the surge chamber is opened, a sudden surge of fluid flows
into the lower
pressure surge chamber to create the local low pressure condition in a
wellbore region in
communication with the surge chamber after the surge chamber is opened.
Additionally, the
wellbore pressure may be reduced by utilizing the surge chamber as a sink.
[0029] Figure 1 is an illustration of a well treatment system of the present
invention, generally
designated by the numeral 8. Well treatment system 8 includes a surge tool 10.
Surge tool 10 is
run into the wellbore 12 on a converyance 14 (e.g., wireline, slickline,
coiled tubing, other
tubulars, etc.). Other equipment, such as but not limited to, perforating
guns, sensors, fluid
handling equipment, and chemical application tools, may also be conveyed into
the well 12 with
surge tool 10. Surge tool 10 is positioned proximate a section of the
formation interval 16 that is
to be addressed. As shown in Figure 1, formation 16 and wellbore casing 20
have been
perforated as illustrated by tunnels 18. However, it should be noted that it
is not necessary for
perforations 18 to exist prior to activation of surge tool 10.
[0030] Surge tool 10 includes a housing 22 that is sealed from the wellbore 12
environment. It
should be recognized that housing 22 may be a part of a perforating gun.
Housing 22 may be the
housing for perforation gun 42 (Figure 4). Shaped charges 24, referred to
herein as "surge
charges," are disposed within housing 22. The surge charges are illustrated in
Figure 1 by the
penetrations 25 formed through housing 22 when the surge charges are
detonated.
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[0031] Surge tool 10 is described further with reference to Figure IA showing
a cross-sectional
view of surge tool 10 of Figure 1. Housing 22 forms a surge chamber 26 that is
sealed from the
wellbore environment until it is desired to create a pressure change in
wellbore 12. One or more
surge charges 24 are disposed within surge chamber 26 and may be carried by a
loading tube 28.
An initiator line 30, such as a detonating cord or an electrical. or fiber
optic line, is connected to
surge charges 24. Surge charges 24 are shaped charges that are adapted to only
penetrate
housing 22 and not to penetrate, or damage well equipment, such as the
wellbore casing, outside
of housing 22. The surge charges 24 differ from perforating shaped charges
which penetrate the
casing and/or the surrounding formation.
[0032] Surge chamber 26 has an inner pressure that is lower than an expected
pressure in the
wellbore 12 in the interval of formation 16 to be treated. Surge chamber 26
may be filled with. a
fluid, such as, but not limited to air or nitrogen. When surge charges 24 are
detonated, housing
22 is penetrated opening surge chamber 26 to wellbore 12. Fluid from the
wellbore flows into
surge chamber 26 creating a substantially instantaneous underbalance
condition.
[0033] As the fluid flows from wellbore 12 into surge chamber 26, if it is
cooler than the gas
inside surge chamber 26 (as is generally the case), then by heat transfer it
will cool the gas inside
surge chamber 26, thereby dropping its pressure, which further drives
continued fluid inflow
from wellbore 12 into surge chamber 26. This cooling-induced pressure drop
enhances the
underbalance condition described above.
[0034] The change in the wellbore pressure may be controlled by numerous
factors including,
the size of housing 22 and surge chamber 26, the initial and relative
pressures of the wellbore
and the surge chamber, the size of the penetrations through housing 22, the
number of
penetrations formed through housing 22, the amount and type of explosive used
in the surge
charges 24, and the shape and construction of the surge charges.
[0035] Surge charges 24 are adapted to only penetrate housing 22 and not to
perforate or
otherwise damage downhole elements such as the well casing as opposed to
conventional
perforating charges 46 (Figure 4). Conventional perforating charges have deep
concave,
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typically conical, parabolic, or hemispherical, explosive cavities lined with
a high-density,
commonly metallic, liners. Surge charges 24 of the present invention have a
shallow explosive
cavity that may be lined with a very low-density liner or not lined.
[0036] Figure 2 is a top, cross-sectional view of a surge tool 10 of the
present invention. Figure
2 is an example of a linerless shaped charge 24 (surge charge). Surge charge
24 is carried by a
loading tube 28 and is disposed within surge chamber 26 of housing 22. Surge
charge 24
includes a charge casing 24 and an explosive 34. Explosive 24 forms an
explosive cavity 36.
Surge charges 24 have a relatively large-radius explosive cavity 36, thus a
shallow explosive
cavity 36, relative to conventional perforating shaped charges.
[0037] Figure 3 illustrates a surge charge 24 including a liner 38. Liner 38
is applied to
explosive cavity 36. Liner 38 may be applied in any manner available such as
by pressing,
pouring, spraying or painted. Liner 38 is a low-density liner. Liner 38 may be
a metallic or non-
metallic liner, constructed of a material such as, but not limited to,
plastic, salt and sand.
Utilization of a liner 38 may permit the use of a smaller amount of explosive
34 when desired.
[0038] As illustrated in Figures 2 and 3, housing 22 may further include a
thinned wall, or
scalloped section 40 formed adjacent the explosive cavity 36. Thinned wall
section 40 may
facilitate penetration of housing 22 when surge charge 24 is detonated and
facilitate the amount
of explosive 34 that is required.
[0039] Figure 4 is an illustration of an embodiment of well treatment system 8
of the present
invention. Well treatment system 8 may include a perforating gun 42 and/or an
applicator tool
44, in combination with a surge tool 10 to create a local transient
underbalance condition.
[0040] Surge tool 10 is described in detail with reference to Figures 1
through 3. The surge
charges are illustrated in Figure 4 by penetrations 25 that are created
through the wall of housing
22 when the surge charges are detonated.
[0041] Perforating gun 42 includes perforating charges 46 that are activatable
to create
perforation tunnels 18 in formation 16 surrounding a wellbore interval and
casing 20.
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Perforation charges 46 typically have a short-radius explosive cavity, thus a
deep explosive
cavity, relative to the surge charges 24. Perforating gun 42 can be activated
by various
mechanisms, such as by a signal communicated over an electrical conductor, a
fiber optic line, a
hydraulic control line, or other type of conduit.
[0042] Well treatment system 8 may further include an applicator tool 44 for
applying a
treatment fluid (e.g., acid, chelant, solvent,. surfactant, brine, oil, enzyme
and so forth, or any
combination of the above) into the wellbore 12, which in turn flows into the
perforation tunnels
18. The treatment fluid applied can be a matrix treatment fluid. Applicator
tool 44 may include
a pressurized chamber 63 containing the treatment fluid. Upon opening of a
port 50, the
pressurized fluid in chamber 63 is communicated into the surrounding wellbore
interval.
Alternatively, applicator tool 44 is in communication with a fluid conduit
that extends to the well
surface. The treatment fluid is applied down the fluid conduit to applicator
tool 44 and through
port 50 to fill the surrounding wellbore interval. The fluid conduit for the
treatment fluid can be
extended through conveyance 14. Alternatively, fluid conduit may run external
to conveyance
14.
[0043] In operation, as shown in Figure 5 with reference to Figures 1 through
4, well treatment
apparatus 8 is lowered at 60 to a wellbore interval. Treatment fluid(s) may
then be applied (at
62) by opening port 50 of applicator tool 44. In some cases, the application
of the treatment
fluid(s) is controlled according to a time release mechanism 52. The rate of
dispensing the
treatment fluid(s) is selected to achieve optimal performance. In other
embodiments, time
release mechanism 52 can be omitted. Perforating gun 42 is then activated at
64 to fire shaped
charges in the perforating gun to extend perforation tunnels 18 into the
surrounding formation
60.
[0044] Upon activation of perforating gun 42, a transient overbalance
condition is created. The
time period of such an overbalance condition can be relatively short (e.g., on
the order of
milliseconds). This overbalance conditions causes the injection at 66 of
treatment fluid into
perforation tunnels 18. The timing of application of the treatment fluid(s) 62
can be selected to
coincide substantially with the activation of the perforating gun 64 such that
the treatment
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fluid(s) can be injected 66 into the perforation tunnels 18 in the presence of
the transient
overbalance condition.
[0045] To achieve a longer period of overbalance, a tubing conveyed
perforating gun can be
employed such that pressurized fluid is applied through tubing to create the
overbalance
condition in the desired interval. An overbalance of thousands of pounds per
square; inch (psi)
can typically be achieved by tubing conveyed perforating guns.
[0046] In some cases, such as with carbonate reservoirs, it may be desirable
to apply acid into
perforation tunnels 18. Conventionally, diversion of such acid occurs such
that the acid flows
unequally into the various perforation tunnels 18, due to the fact that the
acid tends to flow more
to paths of least resistance. However, by timing the application substantially
simultaneously
with the transient overbalance created due to perforating, a more equal
distribution of acid into
perforation tunnels 18 can be achieved. The more uniform distribution of acid
in perforation
tunnels 18 is achieved by application of the acid in a relatively short period
of time (e.g.,
milliseconds). This process is referred to a dynamic diversion. The injection
of acid into each
perforation tunnel 58 provides near-wellbore stimulation, which acts to
enhance a subsequent
cleanup operation.
[0047] Surge tool 10 is activated 68 to create the local transient
underbalance condition. This
causes a flow of fluid and debris out of perforation tunnels 18 into the
wellbore such that cleanup
of perforation tunnels 18 can be achieved. Further operations, such as
fracturing and/or gravel
packing, can then be performed at 70. Prior to, at the same time, or after the
further operations
70, the wellbore interval can be set 72 to any one of an overbalance
condition, underbalance
condition, or balanced condition.
[0048] As noted above, a sequence of different pressure conditions are set in
the wellbore
interval adjacent the formation in which perforation tunnels 18 are created.
The pressure
conditions include overbalance conditions, underbalance conditions, and
balanced conditions.
Any sequence of such conditions can be created in the wellbore interval. The
examples
discussed above refers to first creating an overbalance condition to allow the
injection of
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treatment fluids into perforation tunnels, followed by a transient
underbalance condition to clean
out the perforation tunnels. After the transient underbalance, another
pressure condition is later
set in the wellbore interval. The following charts in Figures 6-10 illustrate
different sequences of
pressure conditions that can be set in the wellbore interval.
[0049] Figure 6 shows a chart to illustrate wellbore pressure and reservoir
pressure over time
(from 0 to 0.5 seconds) beginning at the activation of perforating gun 42 at
64. The target
wellbore interval starts with an overbalance condition (where the wellbore
pressure is greater
than the reservoir pressure). A dynamic underbalance is then created (where
the wellbore
pressure is less than the reservoir pressure), indicated as 500. As shown in
the example of Figure
6, the dynamic underbalance condition extends a period that is less than 0.1
seconds in duration.
Later, after the dynamic underbalance at 500, the wellbore interval is set at
an overbalance
condition.
[0050] Figure 7 shows another sequence, in which the wellbore interval starts
in the overbalance
condition, with a transient underbalance at 502 created shortly after the
initial overbalance
condition. Later, an underbalance condition is maintained.
[00511 Figure 8 shows another sequence, in which the wellbore interval starts
in an overbalance
condition, with a transient pressure dip 506 created in which the wellbore
pressure is reduced but
stays above the reservoir pressure. Next, the wellbore pressure is reduced
further such that it is
balanced at 508 with respect to the reservoir pressure. Later, the wellbore
pressure is set at a
pressure to provide an overbalance condition.
[0052] Figure 9 shows another chart in which the wellbore pressure starts
overbalanced, and is
followed by a dip in the wellbore pressure to first create a transient
condition in which the
wellbore pressure remains overbalanced (indicated as 510). Next, another
transient condition is
created in which the wellbore pressure is dropped further such that an
underbalance condition is
created (indicated as 512). Later, the wellbore pressure is elevated to
provide an overbalance
and finally the wellbore pressure and reservoir pressure are balanced.
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[0053] Figure 10 shows another example sequence, in which the wellbore
interval starts
underbalanced 514, followed by a transient overbalance (516). After the
transient overbalance, a
transient underbalance 518 is created. Later, the wellbore interval is kept at
the underbalance
condition.
[0054] The charts in Figures 6-10 are illustrative examples, as many other
sequences of pressure
conditions can be set in the wellbore interval, according to the needs and
desires of the well
operator.
[0055] From the foregoing detailed description of specific embodiments of the
invention, it
should be apparent that a well treatment system and method that is novel has
been disclosed.
Although specific embodiments of the invention have been disclosed herein in
some detail, this
has been done solely for the purposes of describing various features and
aspects of the invention,
and is not intended to be limiting with respect to the scope of the invention.
It is contemplated
that various substitutions, alterations, and/or modifications, including but
not limited to those
implementation variations which may have been suggested herein, may be made to
the disclosed
embodiments without departing from the spirit and scope of the invention as
defined by the
appended claims which follow.
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