Note: Descriptions are shown in the official language in which they were submitted.
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METHODS AND EQUIPMENT TO IMPROVE RELIABILITY OF PINPOINT
STIMULATION OPERATIONS
BACKGROUND
[0001] The present invention relates to subterranean stimulation operations
and,
more particularly, to apparatuses and methods for improving the reliability of
pinpoint
stimulation operations.
[0002] To produce hydrocarbons (e.g., oil, gas, etc.) from a subterranean
formation, well bores may be drilled that penetrate hydrocarbon-containing
portions of the
subterranean formation. The portion of the subterranean formation from which
hydrocarbons
may be produced is commonly referred to as a "production zone." In some
instances, a
subterranean formation penetrated by the well bore may have multiple
production zones at
various locations along the well bore.
[0003] Generally, after a well bore has been drilled to a desired depth,
completion
operations are performed. Such completion operations may include inserting a
liner or casing
into the well bore and, at times, cementing a casing or liner into place. Once
the well bore is
completed as desired (lined, cased, open hole, or any other known completion)
a stimulation
operation may be performed to enhance hydrocarbon production into the well
bore. Where
methods of the present invention reference "stimulation," that term refers to
any stimulation
technique known in the art for increasing production of desirable fluids from
a subterranean
formation adjacent to a portion of a well bore. Examples of some common
stimulation
operations involve hydraulic fracturing, acidizing, fracture acidizing, and
hydrajetting.
Stimulation operations are intended to increase the flow of hydrocarbons from
the subterranean
formation surrounding the well bore into the well bore itself so that the
hydrocarbons may then
be produced up to the wellhead.
[0004] One suitable hydrajet stimulation method, introduced by Halliburton
Energy Services, Inc., is known as the SURGIFRAC and is described in U.S. Pat.
No. 5,765,642.
The SURGIFRAC process may be particularly well suited for use along highly
deviated portions
of a well bore, where casing the well bore may be difficult and/or expensive.
The SURGIFRAC
hydrajetting technique makes possible the generation of one or more
independent, single plane
hydraulic fractures. Furthermore, even when highly deviated or horizontal
wells are cased,
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hydrajetting the perforations and fractures in such wells generally result in
a more effective
fracturing method than using traditional perforation and fracturing
techniques.
[0005] Another suitable hydrajet stimulation method, introduced by Halliburton
Energy Services, Inc., is known as the COBRAMAX-H and is described in U.S.
Pat. No.
7,225,869. The COBRAMAX-H process may be particularly well suited for use
along highly
deviated portions of a well bore. The COBRAMAX-H technique makes possible the
generation of one or more independent hydraulic fractures without the
necessity of zone
isolation, can be used to perforate and fracture in a single down hole trip,
and may eliminate
the need to set mechanical plugs through the use of a proppant slug.
[0006] Current pinpoint stimulation techniques suffer from a number of
disadvantages. For instance, during hydrajetting operations, the movements of
the
hydrajetting tool generally reduces the tool performance. The movements of the
hydrajetting
tool may be caused by the extension or shrinkage of the pipe or the tremendous
turbulence
around the tool The reduction in tool performance is generally compensated by
longer jetting
times so that a hole is eventually created. However, the increase in jetting
times leads to an
inefficient and time consuming hydrajetting process.
[0007] The COBRAMAX-H process also suffers from some drawbacks.
Specifically, the COBRAMAX-H process involves isolating the hydrajet
stimulated zones
from subsequent well operations. The primary sealing of the previous regions
in the
COBRAMAX-H process is achieved by placing sand plugs in the zones to be
isolated. The
placement of sand plugs, particularly in horizontal well bores, requires a
very low flow rate
which is difficult to achieve when using surface pumping equipment. Moreover,
when the
operating pressures are high, the orifices of the tool must be very small to
create a low flow
rate. The small size of the orifices makes them susceptible to plugging.
[0008] Finally, the SURGIFRAC process which uses the Bernoulli principle to
achieve sealing between fractures poses certain challenges. During the
SURGIFRAC
process, the primary flow goes to the fracture while the secondary, leakoff
flow, is supplied
by the annulus. In some instances, such as in long horizontal well bores, a
large number of
fractures may be desired. The formation of each fracture results in some
additional leakoff.
Consequently, with the increase in the number of fractures, the amount of the
secondary,
leakoff
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flow increases and eventually exceeds the amount of the primary flow to the
fracture. The
increased fluid losses reduces the efficiency of the operations and increases
the cost.
SUMMARY
[0009] The present invention relates to subterranean stimulation operations
and,
more particularly, to apparatuses and methods for improving the reliability of
pinpoint
stimulation operations.
[0010] In one embodiment, the present invention is directed to a pinpoint
stimulation improvement apparatus comprising: an elastomeric element; a spring
positioned on
an inner surface of the elastomeric element; and a flow limiter coupled to the
elastomeric
element.
[0011 ] In another embodiment, the present invention is directed to a flow
limiter
device, comprising: an inner tubing; a pressure reducing channel on an outer
surface of the inner
tubing; an inlet from the inside of the inner tubing to the pressure reducing
channel; and an outlet
from the pressure reducing channel to the inside of the inner tubing.
[0012] In yet another embodiment, the present invention is directed to a
pressure
control module comprising: a seat body, wherein the seat body may be sealed
within an outer
body; an opening on the seat body; and a ball, wherein the ball is inserted in
to the seat body
through the opening.
[0013] In another embodiment, the present invention is directed to a method of
creating a sand plug comprising: pumping a process fluid through a pinpoint
stimulation
improvement apparatus; passing the process fluid through a flow limiter
device, wherein passing
the process fluid through a flow limiter device comprises passing the process
fluid through a
pressure reduction channel; introducing the process fluid at a desired
location; and creating a
sand plug at the desired location.
[0014] In one embodiment, the present invention is directed to a method of
improving the performance of a stimulation jetting tool comprising: pumping a
process fluid
through the stimulation jetting tool; passing a portion of the process fluid
through a pinpoint
stimulation improvement apparatus, wherein the pinpoint stimulation
improvement apparatus
comprises: an elastomeric element; a spring positioned on an inner surface of
the elastomeric
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element; and a flow limiter coupled to the elastomeric element; and expanding
the elastomeric
element to form a hold down mechanism for the stimulation jetting tool.
[0015] The features and advantages of the present invention will be apparent
to
those skilled in the art from the description of the preferred embodiments
which follows when
taken in conjunction with the accompanying drawings. While numerous changes
may be made
by those skilled in the art, such changes are within the spirit of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] These drawings illustrate certain aspects of some of the embodiments of
the present invention, and should not be used to limit or define the
invention.
[0017] FIGURE 1 is a perspective view of a Pinpoint Stimulation Improvement
Apparatus in accordance with an exemplary embodiment of the present invention.
[0018] FIGURE 2 is a cross-sectional comparison of an inflatable packer with a
hold down implementation of a Pinpoint Stimulation Improvement Apparatus in
accordance with
an exemplary embodiment of the present invention.
[0019] FIGURE 3 is a flow limiter in accordance with an exemplary embodiment
of the present invention.
[0020] While embodiments of this disclosure have been depicted and described
and are defined by reference to example embodiments of the disclosure, such
references do not
imply a limitation on the disclosure, and no such limitation is to be
inferred. The subject matter
disclosed is capable of considerable modification, alteration, and equivalents
in form and
function, as will occur to those skilled in the pertinent art and having the
benefit of this
disclosure. The depicted and described embodiments of this disclosure are
examples only, and
not exhaustive of the scope of the disclosure.
DETAILED DESCRIPTION
[0021] The present invention relates to subterranean stimulation operations
and,
more particularly, to apparatuses and methods for improving the reliability of
pinpoint
stimulation operations.
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[0022] Turning now to Figure 1, a Pinpoint Stimulation Improvement Apparatus
(PSIA) in accordance with an exemplary embodiment of the present invention is
denoted
generally by reference numeral 100. The PSIA 100 may comprise one or more flow
limiters
102, an elastomeric element 104 and a spring-mandrel 106 placed on the inner
surface of the
elastomeric element. The spring-mandrel 106 is stiff and provides some
flexure, while acting as
a resetting mechanism to the elastomeric element 104. Additionally, the spring-
mandrel 106
provides a free flow between the area behind and inside the mandrel. In one
exemplary
embodiment, "blanked" areas may be placed strategically to allow installation
of chokes to
promote flow through the outside section of the spring-mandrel 106, thereby
continuously
clearing the area from sand or proppants. Specifically, chokes are placed a
few places (as at the
blanked sections) to insure that a portion of the flow always goes through the
outside of the
spring-mandrel 106 and hence, that no sand or proppants are trapped in the
elastomeric cavity.
[0023] The elastomeric element 104 performs as a hold down device. Figure 2
depicts a cross sectional comparison of an elastomeric element used as an
inflatable packer
configuration with the elastomeric element hold down configuration in
accordance with an
exemplary embodiment of the present invention. Specifically, Figure 2 is
divided into two
regions: the traditional packer implementation 202 (above the centerline) and
the new hold down
configuration 204 (below the centerline). In the packer implementation 202 the
elastomeric
element 206 is pressurized such that a total seal occurs between the top and
bottom (right and left
of Figure 2) of the packer. The pressure achieved must be high enough so that
the elastomeric
element 206 is completely deformed, forming a competent seal. The slats 208 in
the packer
implementation 202 are permanently deformed, with the deformation becoming
more
pronounced after each cycle. The pressurization of the packer implementation
202 may be
achieved using a clean fluid 210. The clean fluid 210 is placed in the cavity
212 through the
cavity opening 214 and the cavity opening 214 is closed, leaving the packer
set. To unset the
packer, the cavity opening 214 must be manually opened.
[0024] In contrast, with the hold down implementation 204, the elastomeric
element 216 may be pressurized by a process fluid 218 such as a sand slurry or
an acid, often
containing sand or other particles. The pressure of the process fluid 218 is
pro-rated using a
pressure reduction system, discussed in more detail below. Because the
pressure is pro-rated, the
low pressure of the process fluid 218 inflates the elastomeric element 216
just enough to touch
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the outside walls (not shown), without causing a complete seal. Sealing is not
the primary object
of the hold down implementation and unlike the packer implementation, fluid
flow remains
continuous through the tool, as well as around the tool, from the top to the
bottom (from right to
left in Figure 2) of the tool. Moreover, in the hold down implementation, the
elastomeric
element 216 is not deformed. The elastomeric element 216 is strengthened and
protected by slats
220 which are either outside of the elastomeric element 216 or covered within
it (not shown).
The outer slats 220 are stretched by the spring-mandrel 106. As a result, the
elastomeric element
216 deflates as soon as the process fluid 218 ceases to be pumped through the
tool. Thus, the
hold down capabilities of the PSIA 100 perform as an anchoring mechanism
allowing the tool to
be maintained at a fixed position for a desired period before deflating and
allowing it to move to
a second desired location. As the elastomeric element 216 deflates, the spring-
mandrel 106
collapses the elastomeric element 216 back in position and the PSIA 100 is
dislodged from its
location.
[0025] In one embodiment, the PSIA 100 in accordance with an exemplary
embodiment of the present invention may be utilized to improve the performance
of a
hydrajetting tool. Specifically, the tool movements due to pipe
extension/shrinkage, temperature
and/or pressure can be minimized by engaging the hold down implementation of
the PSIA 100.
As would be appreciated by those of ordinary skill in the art, with the
benefit of this disclosure,
the strength requirements for the hold-down device are minimal. For instance,
in a vertical well,
a 10000 ft. tubing, 2-3/8" - 4.7 lb./ft. would only need 3800 lbs. to stretch
a full 1 ft.; or about
319 lb./in. As would be appreciated by those of ordinary skill in the art,
with the benefit of this
disclosure, in reality, this value will have to be subtracted by some large
unknown value,
representing friction with the wellbore wall. Note that, even in "vertical"
wells, wells are never
truly vertical; some slants occur during the drilling of the well. In
horizontal wells, movement
can sometimes be large due to the "jerkiness" of the system. However, the pipe
friction negates
some of this movement. For instance, for a 2000 ft. tubing as in the above
example, in a
horizontal well, assuming a friction factor of 0.35 between the pipe and the
well bore wall, the
friction force may be close to 3290 lbs, thus needing an additional help of
only 500 lbs to prevent
the tool's movement. Similarly, the jet reaction force causes some small side
movements of the
tool. For instance, a 0.25" jet at a pressure of 5000 psi may produce a 400
lb. thrust.
Consequently, some small additional force will suffice in preventing the
movements of a
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hydrajetting tool during operation. When in the hold down implementation, the
PSIA 100
provides a flexible, elastomeric hold down system which minimizes the tool
movements and
improves the efficiency of the hydrajetting process.
[0026] As depicted in Figure 1, the PSIA 100 comprises one or more flow
limiting devices 102. Figure 3 depicts a flow limiting device 102 in
accordance with an
exemplary embodiment of the present invention. As depicted in Figure 3, the
fluid is routed
through a pressure reducing channel 300, which wraps around the outer surface
of the inner
tubing 302 a multitude of times. The fluid enters the pressure reducing
channel through the inlet
304. The friction pressure drop due to the continuous turn becomes very high,
even though the
channel size is quite big. As the fluid flows through the pressure reducing
channel 300, the fluid
flow rate is also reduced. The fluid, now having a lower flow rate, then exits
the pressure
reducing channel 300 through an outlet (not shown) and flows back into the
inside of the inner
tubing 302. In one exemplary embodiment, as depicted in Figure 3, the channel
may be
intercepted at three points (e.g., 306), thus bypassing a portion of the
channel for pressure
control.
[0027] As depicted in Figure 3, in one exemplary embodiment, the flow limiting
device 102 may further comprise one or more pressure control modules 308a,
308b, and 308c.
In one embodiment, the pressure control modules 308a, 308b, and 308c may be
ball seat
arrangements. The ball seat arrangement includes a seat body 310. The seat
body 10 is arranged
so that it can be sealed within the flow limiting device 102. A ball 312 may
be inserted into the
seat body 310 through an opening (not shown). Once the ball 312 is inserted
into the seat body
310, it is caged therein. Although Figure 3 depicts three ball seat modules
308a, 308b, and 308c,
as would be appreciated by those of ordinary skill in the art, with the
benefit of this disclosure, a
different number of ball seat modules may be utilized. Removing each ball seat
module 308
bypasses a portion of the pressure reducing channel 300 through ports located
just above. each
potential ball seat module position. These ports connect the channel 300 to
the inside of the
inner tubing. Although the pressure control modules 308 are discussed in
conjunction with the
flow limiting device 102, as would be appreciated by those of ordinary skill
in the art, with the
benefit of this disclosure, the pressure control modules 308 may be used
independently as a
general purpose check valve.
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[0028] In one exemplary embodiment, the ball seat arrangement of the pressure
control modules 308a, 308b, and 308c may also perform as a check valve.
Specifically, the ball
seat arrangement may permit fluid flow from the bottom to the top of the PSIA
100 of Figure 1
for cleaning purposes. Moreover, the ball seat modules 308 may provide a high
flow rate return
line for the fluids that are pumped down the annulus while maintaining a low
flow rate for the
fluids being pumped down through the PSIA 100.
[0029] In one embodiment, it may be desirable to control the pressure of the
fluid
flowing through the elastomeric element. In one exemplary embodiment, two or
more flow
limiting devices 102 may be used as shown in Figure 1. The pressure control
units may be set
with multiple combinations so that the intended pressure and flow is reached.
[0030] In one embodiment, the present invention may be utilized in conjunction
with the COBRAMAX-H process where the creation of solid sand plugs are
required for the
process. This sand plug creation depends upon the ability to pump sand
slurries at a very low
flow rate. Typically, the high pressure of the fluids results in a high flow
rate. The flow limiting
device 102 may be used to reduce the flow rate to as low as 1/2 bpm (barrels
per minute) without
using extra small chokes that would tend to plug when exposed to sand.
Therefore, the PSIA
100 allows the placement of competent sand plugs at desired locations. To
achieve a similar
result using conventional chokes, a 0.09" choke must be utilized which would
potentially plug
with sand that is 30 Mesh or greater. Although a flow limiting device 102 in
accordance with an
exemplary embodiment of the present invention has some size limitations, it
can be designed to
accept 8 Mesh or even larger particles.
[0031 ] In another exemplary embodiment, the present invention may be used in
conjunction with SURGIFRAC operations. Specifically, once a first fracture is
created during
the SURGIFRAC operations, the hydrajetting tool is moved to a second location
to create a
second fracture. However, some of the fluids that are being pumped into the
annulus will leakoff
into the already existing fracture. As the number of fractures increases, the
amount of fluid that
leaks off also increases. The hold down implementation of the PSIA 100 reduces
the amount of
leak off fluid flow through the annulus from the hydrajetting tool (not shown)
to the existing
fractures. Specifically, as the elastomeric element 206 inflates, it restricts
the path of the leak of
fluid flow, thereby reducing the amount of fluids leaked off. Consequently,
the PSIA 100 will
reduce the annulus flow requirement while maintaining pore-pressure and
limited flow influx to
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let the fracture slowly close without producing proppants back into the
wellbore after fluid
injection has stopped.
[0032] As would be appreciated by those of ordinary skill in the art, with the
benefit of this disclosure, the term "pinpoint stimulation" is not limited to
a particular dimension.
For instance, depending on the zones to be isolated, the area subject to the
"pinpoint stimulation"
may be a few inches or in the order of tens of feet in size. Moreover,
although the present
invention is disclosed in the context of "stimulation" processes, as would be
appreciated by those
of ordinary skill in the art, the apparatuses and methods disclosed herein may
be used in
conjunction with other operations. For instance, the apparatuses and methods
disclosed herein
may be used for non-stimulation processes such as cementing; in particular
squeeze cementing or
other squeeze applications of chemicals, fluids, or foams.
[0033] As would be appreciated by those of ordinary skill in the art, although
the
present invention is described in conjunction with a hydrajetting tool, it may
be utilized with any
stimulation jetting tool where it would be desirable to minimize tool movement
and/or fluid leak
off. Moreover, as would be appreciated by those of ordinary skill in the art,
with the benefit of
this disclosure, any references to the term "sand" may include not only quartz
sand, but also
other proppant agents and granular solids. Additionally, as would be
appreciated by those of
ordinary skill in the art, with the benefit of this disclosure, although the
present invention is
described as using one PSIA, two or more PSIAs may be used simultaneously or
sequentially in
the same application to obtain desired results, without departing from the
scope of the present
invention.
[0034] Therefore, the present invention is well-adapted to carry out the
objects
and attain the ends and advantages mentioned as well as those which are
inherent therein. While
the invention has been depicted and described by reference to exemplary
embodiments of the
invention, such a reference does not imply a limitation on the invention, and
no such limitation is
to be inferred. The invention is capable of considerable modification,
alteration, and equivalents
in form and function, as will occur to those ordinarily skilled in the
pertinent arts and having the
benefit of this disclosure. The depicted and described embodiments of the
invention are
exemplary only, and are not exhaustive of the scope of the invention.
Consequently, the
invention is intended to be limited only by the spirit and scope of the
appended claims, giving
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full cognizance to equivalents in all respects. The terms in the claims have
their plain, ordinary
meaning unless otherwise explicitly and clearly defined by the patentee.
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