Note: Descriptions are shown in the official language in which they were submitted.
HYDRAULIC SET PACKER SYSTEM AND FRACTURING METHODS
Field of the Invention
[0001] The present invention relates to a hydraulic set packer system and
methods for
fracturing a zonc of interest in a subterranean formation with a hydraulic set
packing system
through a wellbore for the production of oil, gas or other formation fluids,
Background of the Invention
[00021 Packer systems are used to isolate zones of a wellbore casing for
fracturing and
stimulation processes in the production of oil and gas. A conventional packer
includes a
cylindrical expandable sealing element that engages the inner surface of a
wellbore casing and
thereby prevents the passage of fluids above or below the packer within the
casing.
100031 In a fracturing method, two packers disposed at a distance from each
other within the
casing will isolate a zone of interest between them in the formation rock.
Fracturing fluid is
then pumped into the isolated zone at a very high rate sufficient to increase
the fluid pressure.
This increased pressure causes the surrounding formation rock to crack, and
the fluid enters
into and propagates the crack, Solid proppants, such as sand, may be added to
the fracture
fluid to maintain the crack in an open position and thereby form a high
permeability conduit
through which the formation fluids can flow into the wellbore.
[0004] Typically packers are set in the wellbore casing by inserting the
packer into the easing
using production tubing or wire line tools. When the packer reaches the
desired depth, axial
load is applied to the sealing element by mechanical force, hydraulic pressure
or a
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combination thereof to cause the sealing element to expand radially and engage
the inner
surface of the wellbore casing and thereby plug the wellbore.
[0005] Operational problems are well known in the use of packers. Wear of the
sealing
elements may impair the effectiveness of the packer. Packers may inadvertently
become
stuck during the setting process or be difficult to retrieve. Therefore, there
is a continuing
need to improve the state of the art in packer technology used in wellbore
fracturing for
production of formation fluids.
SUMMARY OF THE INVENTION
[0006] A hydraulic set packer system includes an upper assembly directly
responsive to
fracturing fluid pressure to provide an upper seal for the zone of interest;
and a lower
assembly directly responsive to fracturing fluid pressure to allow fracturing
fluid to flow into
the zone of interest and indirectly responsive to fracturing fluid pressure
through a self-
contained hydraulically sealed lower chamber to provide a lower seal for the
zone of interest.
By increasing and decreasing the fracturing fluid pressure, the hydraulic set
packer system
may be used alternately to seal and isolate the zone of interest, and to
easily unseal and
retrieve or move the packer system.
[0007] In one aspect, the invention comprises a hydraulic set packer system,
having radial and
axial directions, for use and connection with production tubing, comprising:
(a) an upper assembly defining an internal bore in fluid
communication with the
production tubing, an elastomeric annular upper seal, an upper piston, wherein
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fluid pressure in the internal bore actuates the upper piston to compress the
upper seal and expand the upper seal radially; and
(b) a lower assembly defining a frac port in fluid communication with
the upper
assembly internal bore, a frac piston which reciprocates between a closed
position which occludes the frac port, and an open position which does not
occlude the frac port, an elastomeric annular lower seal, an internal
hydraulic
lower piston chamber, and a lower piston, wherein fluid pressure in the upper
assembly internal bore acts on the frac piston to move it to its open
position,
and wherein movement of the frac piston to its open position compresses the
internal hydraulic lower piston chamber to actuate the lower piston to
compress the lower seal and expand the lower seal radially.
[0008] in another aspect, the invention comprises a method of fracturing a
formation rock
zone of interest with a hydraulic set packing system through a wellbore using
a hydraulic set
packer as described,
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] In the drawings, like elements are assigned like reference numerals.
The drawings are
not necessarily to scale, with the emphasis instead placed upon the principles
of the present
invention. Additionally, each of the embodiments depicted are but one of a
number of
possible arrangements utilizing the fundamental concepts of the present
invention. The
drawings are briefly described as follows:
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[0010] FIG. 1 is an elevation view of the upper assembly of the hydraulic set
packer system
connected to cross-over subs;
[0011] FIG. 2 is an elevation view of the lower assembly of the hydraulic set
packer system
connected to a cross-over sub;
[0012] FIG. 3 is a larger scale elevation view of the upper assembly of the
hydraulic set
packer system shown in FIG. 1 between line A and line 11;
[0013] FIG. 4 is a larger scale enlarged view of the lower assembly of the
hydraulic set
packer system of FIG. 2 between line C and line D.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0014] The present invention relates to a hydraulic set packer system and
inethods for
fracturing a zone of interest in formation rock with a hydraulic set packing
system through a
wellbore for the production of oil, gas or other formation fluids. When
describing the present
invention, all terms not defined heroin have their common art-recognized
meanings. To the
extent that the following description is of a specific embodiment or a
particular use of the
invention, it is intended to be illustrative only, and not limiting of the
claimed invention. The
following description is intended to cover all alternatives, modifications and
equivalents that
are included in the spirit and scope of the invention, as defined in the
appended claims.
[0015] The terms "upper" and ''lower" as used herein denote the relative
positions of various
elements or components when the system is deployed in a substantially vertical
orientation.
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[00161 As shown in Figure 1 and 2, a hydraulic set packer system comprises an
upper
assembly (1) having an upper seal and a lower assembly (8) having a lower
seal. The upper
assembly and the lower assembly are connected by a pup joint, the length of
which will define
the fracturing zone between the upper and lower assemblies.
[00171 As shown in Figure 1, the upper assembly (1) comprises an upper mandrel
(3), upper
seal (4), upper piston (5) and upper housing (6). The upper seal (4) is
typically constructed
with rubber or other elastomer or other material having sealing and
deformation properties
suitable for use at high pressure and temperature. Suitable sealing material
is well known in
the art.
[00181 As shown in Figure 3, the upper mandrel (3) defines a through bore and
has a widened
upper cross-section defining an upper seal retaining lip (3a), a narrower
lower-eross section
defining an upper spindle (3b), and a lower spindle (3c). The lower spindle
defines at least
one port (3d). The annular upper seal (4) fits tightly around the upper
spindle (3b) and is
retained at its top end by the upper retainer (3a) and at its bottom end by
the upper piston (5).
The annular upper piston (5) is retained at its top end by the upper seal (4)
and its bottom end
by the upper housing (6). A crossover sub (7) is connected to the upper
housing (6) and
provides a connection to a pup joint (not shown) which spans between the upper
and lower
assemblies.
[0019] The upper housing (6) is connected at its top end to the lower spindle
(3c) of the upper
mandrel (3) by a sealed threaded connection. The upper housing (6), upper
spindle (3b),
upper port (3d) and upper piston (5) collectively define an upper piston
chamber (6a) in fluid
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communication with the through bore of the upper mandrel (3) through ports
(3d). The upper
piston (5) is disposed within the piston chamber and fits around the upper
spindle (3b), and
reciprocates slidingly around the upper spindle (3b) and lower spindle (3c)
within the upper
housing (6), 0-ring seals (5a, 5b) seal the upper piston chamber. Upper
chamber seal (6b)
provides a seal below the upper chamber (6a).
[0020] The top of the upper piston (5) defines a seal retaining lip and bears
on the seal. A
spring or other biasing means (not shown) may be provided in the space between
the upper
mandrel (3) and the upper piston (5) to bias the upper piston to a lower
position.
[0021] As shown in Figure 2, in one embodiment, the lower assembly (8)
comprises a
crossover sub (9) which connects to the lower end of a pup joint (not shown),
a frac sub (10)
defining at least one frac port (10a), a frac piston (11), a frac housing
(12), a lower mandrel
(14), a lower seal (15), a lower piston (16) and a lower sub (17). The lower
seal (15) is
typically constructed with rubber, or other elastomer, or other material
having sealing and
deformation properties suitable for use at high pressure and temperature.
Suitable sealing
materials are well known in the art.
[0022] As shown in Figure 4, the frac sub (10) has an inner bore and frac
ports (10a) that are
in fluid communication with the upper bore (3c) of the upper assembly (1). The
frac housing
(12) is connected at its top end to the bottom end of the frac sub (10) by
sealed threaded
connection. The lower mandrel (14) is connected at its top end to the bottom
end of the frac
housing (12) by a sealed threaded connection. The lower mandrel (14) defines a
through bore
and has a widened upper cross-section having a lower seal retaining lip (14a),
a narrower
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lower-cross section defining an upper spindle (14b), and a lower spindle
(14c), The lower
spindle extends into thc lower sub (17) and defines a port (14d) which
provides fluid
communication to the lower mandrel (14) throughbore.
[0023] The frac piston (11) is inserted into and sealingly reciprocates within
frac housing (12)
and the frac sub (10) between a closed position in which the upper end of the
frac piston
occludes the frac ports (10a) and an open position that does not occlude the
frac ports (10a).
0-ring seals are provided which seal the frac piston within the frac housing
(12) and frac
piston seals (11a) are provided which seal the base portion of the frac piston
within the frac
housing (12). A biasing means (13) such as a spring disposed between and
bearing on the base
portion of the frac piston (11) and the top end of the lower mandrel (14)
biases the frac piston
(11) to its closed position.
[0024] The annular lower seal (15) fits tightly around the lower spindle (14b)
and is retained
at its top end by the retaining lip (14a), and at its bottom end by the lower
piston (16). The
annular lower piston (16) bears on the lower seal (4) and is retained within
the bottom sub
(17). The lower piston (16) fits tightly around the lower spindle (14b) but is
capable of sliding
along the lower spindle (14b) and within thc bottom sub (17). The cup-shaped
bottom sub
(17) is connected to the bottom end of the lower mandrel (14) by a sealed
threaded
connection. ,
[0025] The frac housing (12), frac piston (11), lower hydraulic bore (14c),
lower port (14d),
bottom sub (17) and lower piston (16) collectively define a sealed fluid-tight
lower piston
chamber (17a) filled with a hydraulic fluid such as mineral oil or other low
compressibility
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fluid. Lower piston inside seals (16a) and lower piston outside seals (16b)
may be used to
form a tight fit between the lower piston (16) and the lower spindle (14b) and
the inner bore
of the bottom sub (17), respectively.
[0026] In operation, the upper assembly and lower assembly (8) are connected
by a pup joint
(not shown) the length of which defines the zone of interest, between the
upper seal and the
lower seal.
[0027] The upper and lower assemblies are then lowered within the wellbore
casing on coiled
or jointed tubing as is well known in the art, until the lower seal (15) and
the upper seal (4)
reach the depth of the bottom and top, respectively, of the desired isolation
zone in the
subterranean formation.
[0028] Fracturing fluid is then pumped at a high rate into the production
tubing. The
fracturing fluid flows through the upper bore (3c) of the upper assembly (1),
through the
production tubing, and into the frac sub (10) of thc lower assembly (8). At
the upper
assembly (1), the fracturing fluid also flows through the upper bore (3c),
through the upper
port (3d) and into the upper chamber (6a). The attendant hydraulic pressure in
the upper
chamber (6a) is sufficient to displace the upper piston (5) upwards by axial
compression of
the upper seal (4) against the upper retaining lip (3a). As the upper seal (4)
is upwardly
compressed in the axial direction, it expands radially and tightly seals
against the inner
surface of the wellbore casing.
[0029] At the lower assembly (8), the fracturing fluid flows into the frac sub
(10) and against
the top end of the frac piston (11). The attendant hydraulic pressure exerted
on the top end of
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the frac piston (11) is sufficient to overcome the closing force exerted on
the frac piston (11)
by the spring (13). The frac piston (11) is thereby displaced in the downward
axial direction to
its open position allowing fracturing fluid to flow into the surrounding
formation rock through
the frac ports (10a). As the frac piston (11) displaces downward to its open
position, it also
pressurizes the hydraulic fluid in the lower piston chamber (17a). The
attendant hydraulic
pressure in the lower piston chamber (17a) displaces the lower piston (16)
upwards by axial
compression of the lower seal (15) against the lower retainer (14a). As the
lower seal (15) is
upwardly compressed in the axial direction, it expands radially and tightly
seals against the
inner surface of the wellbore casing.
[0030] Once the formation rock has been satisfactorily fractured, the
fracturing fluid pumping
pressure in the production tubing is decreased. Consequently, the hydraulic
pressure within
the upper chamber (6a) decreases and the upper piston (5) displaces downward
as the upper
seal (4) expands axially and contracts radially from the inner surface of the
wellbore casing. If
installed, a spring may also urge the upper piston downwards. The spring may
be necessary if
retraction of the seal does not provide sufficient force to move the upper
piston (5) downward
after pressure in the production tubing is reduced,
[0031] Likewise, the hydraulic pressure on the frac piston (11) decreases and
it is urged
upwards by the spring (13) to its closed position. The hydraulic pressure
within the lower
piston chamber (17a) is thereby decreased, the lower piston (16) moves
downwards, and the
lower seal (15) expands axially and contracts radially from the inner surface
of the wellbore
casing. With the upper seal (4) and the lower seal (15) disengaged from the
inner surface of
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the wellbore casing, the upper assembly (1) and lower assembly (8) may be
retrieved from the
wellbore casing.
[00321 One skilled in the art will recognize that the geometric and mechanical
properties of
the constituent parts of the upper assembly (1) and the lower assembly (8) may
be selected to
allow for a differential between the onset of the upper seal (4) sealing
against the inner
surface of the wellbore casing, the onset of the lower seal (15) scaling
against the inner
surface of the wellbore casing and the onset of fracturing fluid flowing
through the frac ports
(10a) of the frac sub (10).
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