Note: Descriptions are shown in the official language in which they were submitted.
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WELL STTMULATION TOOL AND METHOD OF USING SAME
TECHNICAL FIELD
The invention relates to the stimulation of oil and
gas wells to improve production and, in particular, to a
well stimulation tool used to deliver high-pressure fluids
through a production tubing of a well in order to acidize
and/or fracture subterranean formations with which the well
communicates.
BACKGROUND OF THE INVENTION
It is well known that many oil and gas wells
require stimulation in order to increase production either
as a part of well completion, or as a part of well
workover. Well stimulation involves the pumping of fluids
under high pressure into the annulus of the well in order
to break up subterranean formations and release
hydrocarbons into the wellbore, where they can be extracted
to the surface. Since it is generally not economically
feasible to manufacture wellhead equipment that can
withstand extreme pressures; the wellhead must be isolated
or removed during well stimulation in order to prevent
potential damage and/or injury.
One method of stimulating a well is to pump
high-pressure fluids down a production tubing suspended in
the well. To accomplish this, the production tubing is
plugged and the wellhead is removed from the well. An
extension is then screwed into the top of the tubing hanger
and high-pres ure fluids are pumped through a high-pressure
valve that communicates with a top of the extension. A
high-pressure adapter of this type is described in United
States Patent No. 5,103,900 that issued on April 14, 1992
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to McLeod et al:, and entitled HIGH PRESSURE ADAPTER FOR
WELL-HEADS. McLeod et al. describe an improvement to the
McEvoy PST adapter and pack-off nippla in which vent ports
are added to the McEvoy tubing head adapter to comply with
Ame-rican ,Petroleum Institute (API) regulations respecting
elevations in pressure rating between adjacent adapters.
The McEvoy PST adapter and McLeod et al.'s
improvements to it suffer from several disadvantages,
however. First, each adapter must be constructed for a
specific size of production tubing. Consequently, at least
one adapter must be kept in stock for each size of
production tubing that is to be serviced. Second; the flow
path of high-pressure fluids is interrupted by an internal
bore in the tubing head adapter. The internal bore
provides a space where eddy currents develop in the
high-pressure fluids. The eddy currents tend to cause
abrasive well stimulation fluids to "wash out" a top end of
a pack-off nipple that connects to the tubing hanger. As
is well understood in the art, damage caused by wash out
can cause dangerous pressure leaks.
There therefore exists a need for a well
stimulation tool that permits high-pressure fluids to be
safely pumped down the production tubing of a hydrocarbon
well.
2 5 SU1~2ARY OF THE INVENTION
It is therefore an object of the invention to
provide a well stimulation tool that permits high-pressure
fluids to be safely pumped down the production tubing of a
hydrocarbon well.
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It is a further object of the invention to provide
a well stimulation tool that is quickly and easily mounted
to an exposed tubing hanger of a hydrocarbon well.
The invention therefore provides a well stimulation
tool for stimulating a well having a tubing head mounted to
a casing spoof of the well and a production tubing
suspended from a tubing hanger in. the tubing head. The
well stimulation tool comprises an adapter spool having a
bottom flange adapted for connection to one of a tubing
head and a blowout preventer mounted to the tubing head.
The adapter spool has a top end adapted to receive a
mandrel that can be reciprocally moved through a packing
that surrounds the mandrel and is retained in a packing
cavity in the top end of the adapter spool. The top end of
the adapter spool further includes threads for securing a
lockdown nut that covers the packing and surrounds an outer
periphery of the mandrel.
The mandrel includes a mandrel top end having a
flange adapted for the connection of a high-pressure valve,
and a mandrel bottom end having a thread for the connection
of an adapter pin. The'adapter pin has a top end with
threads for connecting the adapter pin to the mandrel
bottom end. The adapter pin also has a bottom end with
threads for'connecting the adapter pin to the top end of a
tubing hanger.
The well stimulation tool preferabl~r further
includes a high-pressure flange adapted to be mounted to a
top of the high-pressure valve. The high-pressure flange
has a pressure flange bottom end adapted for connection to
a top flange of the high-pressure valve. The high-pressure
flange also has a top end that is threaded for connection
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to a high-pressure line for injecting high-pressure well
stimulation fluids into the well.
In accordance with one embodiment of the invention,
The well stimulation tool further comprises a lifting head
assembly including a first member and a second member. The
first member has a bottom end adapted to be connected to
the high-pressure flange. The second member has means for
connecting a hoist to the well stimulation tool. When the
lifting head assembly is connected to the combination of
the high-pressure flange, high-pressure valve, the adapter
spool, the mandrel and the adapter pin, and hoisted above
the well, the adapter pin extends below the bottom flange
of the adapter pin to facilitate the installation of the
well stimulation tool to the tubing hanger.
The lifting head assembly includes a hollow
cylinder having a lifting head top end and lifting head
bottom end. The lifting head bottom end includes an
aperture. A lifting sub having a top end, which
reciprocates freely within the hollow cylinder but cannot
pass through the aperture in the bottom end, is adapted to
connect to a top end of the high-pressure flange. A
lifting eye is affixed to the lifting head top end.
The lifting head further comprises opposed,.
radially extending lift arms adjacent the lifting head
bottom end, the lift arms respectively including a lift eye
located near an outer end thereof. The lockdown nut also
comprises opposed, radially extending lift arms
respectively including a lift eye located near an outer end
thereof. First and second lifting cables interconnect the
lift arms of the lift head and the lockdown nut.
Consequently, when the well stimulation tool is lifted
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using the lifting eye affixed to the top end of the lifting
head, the.lifting sub top end moves downwardly within the
hollow cylinder and the lifting cables bear the weight of
the lockdown nut and the adapter spool. As a result, the
mandrel is stroked down through the adapter spool and the
adapter pin is extended beneath the bottom flange of the
adapter spool to permit the adapter pin to be connected to,
or disconnected from, the top end of the tubing hanger.
The invention further provides methods for
completing and stimulating oil and gas wells.
BRIEF DESCRIPTION OF THE DRAW2NGS
Further features and advantages of the present
invention will become apparent from the following detailed
description, taken in combination with the appended
drawings, in which:
FIG. 1 is a cross-sectional view of a well
stimulation tool in accordance with one embodiment.of the
invention;
FIG. 2 is a cross-sectional view of a well
stimulation tool connected to a high-pressure valve and in
a suspended position for installation on the well, in
accordance with another embodiment of the invention;
FIG. 3 is a cross-sectional view of the well
stimulation tool with the high-pressure valve shown in
FIG. 2 installed on the well;
FIG. 4 is a detailed cross-sectional view of a
lifting head assembly and a high-pressure flange used with
the well stimulation tool shown in FIGs. 2 and 3;
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FIG. 5 is a schematic cross-sectional view of the
well stimulation tool shown in FIGS. 2 and 3 with a
lubricator that is being used to retrieve a plug from a
production tubing so that the well stimulation tool can be
used to stimulate a hydrocarbon well, without a blowout
preventer;
FIG. 6 is a schematic cross-sectional view of the
well stimulation tool illustrated in FIG. 5 with the
lubricator removed and a high-pressure line connected to
the well stimulation tool; and
FIG. 7 is a schematic cross-sectional view showing
the well stimulation tool shown in FIGS. 2 and 3 with an
elongated adapter pin used to stimulate a hydrocarbon well
through a blowout preventer.
It will be noted that throughout the appended
drawings, like features are identified by like reference
numerals.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention provides a well stimulation tool that
permits high-pressure fluids to be pumped into the well
through a production tubing string suspended in the well by
a tubing hanger. The tool facilitates a fast, sure
connection to the tubing hanger.
FIG. 1 is a cross-sectional view of the well
stimulation tool in accordance with one embodiment of the
invention. The well stimulation tool, generally indicated
by reference numeral 10, includes an adapter spool 12. A
mandrel 14 is received in an axial passage 16 in the
adapter spool 12. The axial passage 16 includes a throat
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region 20 and an adapter pin docking region 22. The
throat 18 retains a steel packing washer 24. High-pressure
packing 26, such as a chevron packing, is retained above
the steel packing washer 24: The high-pressure packing 26
closely surrounds and provides~a high-pressure seal around
the mandrel 14, in order to ensure that well fluids do not
escape to the atmosphere when the adapter spool 12 is
mounted to one of a tubing head spool 102, as shown in
FIG. 3; and a blowout preventer 120 mounted to the tubing
TO head spool 102, as shown in FIG. 7. The high-pressure
packing 26 is retained by a gland nut 28. A lockdown
nut 30 threadedly engages a spiral thread on an outer
periphery of the top end of the adapter spool 12. A top
wall of the lockdown nut 30 projects inwardly to cover the
gland nut 28 in order to ensure that the gland nut 28 is
not stripped by fluid pressures exerted on the
high-pressure packing 26, while being radially spaced apart
from the outer periphery ~of the mandrel 14 in order to
permit free reciprocation of the mandrel 14 within the
axial passage 16 of the adapter spool 12.
An adapter pin 32 has an axial bore 34, and
includes a top end that threadedly engages an external
spiral thread on the bottom end of the mandrel 14, and a
bottom end sized to match a size of a production tubing
(not shown) in the well, for example, 2~"; 2%" or 3~". The
adapter pin 32 is equipped with any required thread pattern
on the bottom end to match tha of a tubing hanger 106
(FIG. 3) from which the tubing is suspended in the well.
Typically, the tubing hanger has E.U.E. threads, which are
well known in the art. The adapter pin 32 is
interchangeable to permit the tool 10 to be connected to
different sizes of tubing hangers. Ring seals 36 are
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g
incorporated in the adapter pin 32 to provide a seal
between the mandrel 14 and the adapter pin 32 to prevent
fluid leakage when high-pressure fluid flows through a
central passage 38 of the mandrel 14 and the central
bore 34 of the adapter pin 32.
The mandrel 14 further includes a stud pad 40
having threaded bores 42 for receiving studs for mounting a
high-pressure valve 64 (FIG. 2) thereon. A bottom
flange 44 of the adapter spool 12 includes mounting
bores 46 for bolting the adapter spool 12 to a top of
another spool, such as a blowout preventer or a tubing head
spool. An annular groove 48 is also provided in the bottom
flange 44 of the adapter spool 12 and the stud pad 40 of
the mandrel l4 respectively, for receiving a gasket seal
(not shown) when the tool 10 is connected between a
high-pressure valve and one of the tubing head spool and a
blowout preventer mounted to the tubing head spool.
The reciprocation of the mandrel 14 within the
axial passage l& of the adapter spool 12 is limited in a
downward direction by the stud pad 40 and in an upward
direction by the adapter pin 32, which has a diameter
greater than that of the throat region 20, and smaller than
that of the docking region 22 of the adapter spool 12.
Thus, the mandrel 14 can reciprocate within the adapter
spool 12 but cannot be removed from the adapter spool 12
when the adapter pin 32 is connected to the mandrel l4.
The adapter spool 12 fur her includes a bleed-off
port 50 which is closed by a needle valve 52, having a
pressure rating of at least 10,000 Psi. The needle
valve 52 is left open during well stimulation treatment so
that any pressure leak is readily detected.
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When the lockdown nut 30 is connected to a service
rig or boom truck (neither one shown) and the well
stimulation tool 10 is hoisted above one of a tubing head
spool and a blowout preventer mounted on the tubing head
spool, the mandrel 14 moves downward under its own weight
and the adapter pin. 32 extends beneath the bottom flange 44
of the adapter spool 12. Thus, the adapter pin 32 can be
visually guided into a connection with the tubing hanger in
the tubing head spool, or inserted through the blowout
preventer mounted on the tubing head spool to be connected
to the tubing hanger irn the tubing head spool. After the
adapter pin 32 is connected to the tubing hanger, the
adapter spool 12 is lowered to permit it to be mounted to
the top of the tubing head spool, or the top of the blowout
preventer. This operation will be further described below
with reference to FIGS. 2 and 3.
FIGS. 2 and 3 illustrate another embodiment of the
invention, generally indicated by numeral 11 which includes
the well stimulation tool 10 illustrated in FIG. 1, and
further includes a high-pressure flange 54 and a lifting
head assembly 56.
The high-pressure flange 54 and the lifting head
assembly 56 are illustrated in detail in FIG. 4: The
high-pressure flange 54 includes a pressure flange top
end 58 having a spiral thread on an outer periphery thereof
for connection of the lifting head assembly 56, a wireline
lubricator, or a high-pressure fluid line, as will be
further described below with reference to FIGS. 5-7. The
high-pressure flange 54 also includes a bottom flange 60
with mounting bores 62 that extend therethrough for bolting
the high-pressure flange 54 to a top of the high-pressure
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valve 64, as shown in FIGS. 2 and 3. An annular groove 66
is provided in the bottom flange 60 for receiving a gasket
seal (not shown) when the high-pressure flange 54 is
mounted to the high-pres ure valve 64 shown in FIGS. 2
and 3. An axial passage 68 extends through the
high-pressure flange 60 for fluid communication with the
high-pressure valve 64.
The lifting head assembly 56 includes a lifting
head 70 and a lifting sub 72. The lifting head 70 includes
a hollow cylinder 74, which has a top end 76 and a bottom
wall 78 that is preferably threadedly secured to a bottom
end thereof. The lifting sub 72 has a side wall 80,
interconnecting a lifting sub bottom end 82 and a lifting
sub top end 84. The lifting sub top end 84 has a diameter
slightly smaller than an inner diameter of the cylinder 74,
and greater than an outer diameter of the side wall 80 so
that the lifting sub top, end 84 is slidingly guided within
the cylinder 74 when the side wall 80 of the lifting sub 72
reciprocates through an axial aperture 86 in the bottom
wall 78 of the cylinder 74. The lifting sub top end 84 is
preferably threadedly connected to the top end of the side
wall 80. The lifting sub bottom end 82 has a diameter
greater than that of the aperture 86 of the bottom wall 78,
so that the aperture 86 of the bottom wall 78 permits free
reciprocation of the lifting sub 72 within the cylinder 74,
but prevents the lifting sub 72 from being removed in
either direction from the cylinder 74. The lifting sub
bottom end 82 further includes a bottom shoulder 88 that
rotatably engages a hammer union 90, which threadedly
engages the spiral thread on the outer periphery of the top
end 58 of the high-pressure flange 54.
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The lifting head 70 further includes a lifting
eye 92, which is used to manipulate the well stimulation
tool 11. The lifting eye 92 is affixed to the top end of
the cylinder 74. The lifting head 70 is provided with a
mechanism for connecting the adapter spool l2 shown in
FIGS. 2 and 3 which, in this embodiment, includes two
opposed radially extending lift arms 94 adjacent to the
bottom end of the lifting head 70. Each of the lift
arms 94 includes a lift eye 96 located near an outer end
thereof. The lockdown nut 30 shown in FIGS. 2 and 3 also
includes two opposed radially extending lift arms 94', with
lift eyes 96' in their respective outer ends.
Corresponding lift arms 94 and 94' on the respective lift
head 70 and the lockdown nut 30 are interconnected by
lifting cables 98 using removable connectors; such as a
clevis 100 that is well known in the art.
A typical well is completed for stimulation by
running a production tubing into the well. The production
tubing is generally run into the well through a blowout
preventer mounted to the top of the tubing head spool.
After the production tubing is run into the well, a tubing
hanger is connected to a top of the production tubing, and
the tubing hanger is inserted through the blowout preventer
and into tubing head spool where it is secured in a manner
well known in the art. In well completion or well
workover, which require a well stimulation procedure, the
well stimulation tool 10 or 11 in accordance with the
invention, can be used to direct high-pressure stimulation
fluids into the well through the production tubing. A
method of using the well stimulation tool 10 or l1 is
described below.
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The stimulation of a hydrocarbon well from which a
blowout preventer has been removed is illustrated in
FIGS. 2, 3, 5 and 6. As an example, the well stimulation
tool 11 is used to illustrate the features and advantages
of the present invention. A boom truck or a rig (not
shown) is used to hoist the combination of the well
stimulation tool 11 and the high-pressure valve 64 by
connecting the hoist (not shown) to the lifting eye 92 at
the top of the lifting head 70. When the combination of
the well stimulation tool 11 and the high-pressure valve 64
is lifted using the lifting eye 92, the lifting cables 98
support the weight of the lockdown nut 30 and the adapter
spool 12. Consequently, the weight of the high-pressure
valve 64, the mandrel 14, the high-pressure flange 54 and
the lifting sub 72 causes the mandrel 14 to stroke down
through the packing 26 in the adapter spool 12 and the
lifting sub 72 to stroke down through aperture 86 in the
lifting, head 70, so that the adapter pin 32 extends beneath
the bottom flange 44 of the adapter spool 12 to an extent,
as shown in FIG. 2, which facilitates the connection of the
adapter pin 32 to a tubing hanger 106 in the tubing head
spool 12 shown in FIG. 3.
The combination of the well stimulation tool 11 and
the high-pressure valve 64 illustrated in FIG. 2 is
suspended over a wellhead to which a tubing head spool 102
(see FIG. 3) is mounted. A production tubing 104 is
suspended from the tubing hanger 106, which is secured in
the tubing head spool 102. The combination of the well
stimulation tool 11 and the high-pressure valve 64 is
lowered and rotated to threadedly engage the bottom end of
the adapter pin.32 with the top end of the tubing
hanger 106 shown in FIG. 3. It should be understood that
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the adapter pin 32 is visible to permit it to be visually
guided into a connection with the tubing hanger 106. This
facilitates the connection and helps to ensure that the
threads on the adapter pin are not damaged. After the
adapter pin 32 is securely connected to the tubing
hanger 106, the boom truck or rig is operated to further
lower the combination of the well stimulation tool 11 and
the high-pressure valve 64, which causes the adapter
spool 12, the lockdown nut 30 and the lifting head 70 to
move downwardly until the adapter spool 12 rests on the top
of the tubing head spool 102 when the high-pressure
valve 64 with the remaining parts of the well stimulation
tool 11 are supported by the tubing hanger 106, as
illustrated in FIG. 3. The bottom flange 44 of the adapter
spool 12 and the top flange of the tubing head spool 102
are then bolted together and the installation of the well
stimulation tool 11 with the high-pressure valve 64 is
thereby completed.
Subsequently, the respective clevises 100 that
connect the lifting cables 98 to the lockdown nut 30 are
released. The hammer union 90 is also released. Thus, the
lifting head assembly 56 with the hammer union 90 can be
removed from the top end of the high-pressure flange 54.
As illustrated in FIG. 5, a lubricator that is well known
in the art, typically a wireline lubricator 108 (which is
schematically illustrated), is then connected to the top
end of the high-pressure flange 54. After the wireline
lubricator 108 is mounted to the top end of the
high-pressure flange 54, the high-pressure valve 64 is
opened and a wireline 110 is run into the production
tubing 104 to retrieve a retrievable plug 112 that is
normally set in the production tubing 104 before it is run
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into the well. The high-pressure valve 64 is then closed
and the wireline lubricator 108 is removed.
Thereafter, a high-pressure line 114, as
illustrated in FIG. 6, is connected to the top end of the
high-pressure flange 54 using a hammer union 116 in a
manner well known in the art. The high-pressure valve 64
is then opened and high-pressure fluids, such as acidizing
or fracturing fluids, are pumped through the high-pressure
flange 54, the high-pressure valve 64, the mandrel 14, the
l0 adapter pin 32, the tubing hanger 106, the production
tubing 104, and into the well.
After the well stimulation procedure is complete,
the stimulation fluids are "flowed back" through the well
stimulation tool 11 and the high-pressure valve 64. When
the flow-back process is complete, the high-pressure
valve 64 is closed and the high-pressure line 114 is
disconnected from the high-pressure flange 54. If the well
contains natural pressure, the tubing must be plugged once
again before the well stimulation tool 11 and the
high-pressure valve 64 can be removed. Consequently, the
wireline lubricator 108 is mounted again to the
high-pressure flange 54 as shown in FIG. 5 and the
wireline 110 is run down to reset the removable plug 112 in
the production tubing 104.
After the plug 112 is set, the wireline 110 is
retrieved and then the wireline lubricator 108 is again
removed from the high-pressure flange 54.
After the wireline lubricator 108 is removed, the
lifting head assembly 56 shown in FIG. 4 is hoisted back to
the top end of the high-pressure flange 54. The lifting
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cables 98 are connected to the respective lifting eyes 96'
in the lockdown nut 30 by re-inserting the clevises 100,
and the lifting sub 72 is connected to the top end of the
high-pressure flange 54 using the hammer union 90. The
adapter spool 12 is then unbolted from the tubing head
spool 102 and a hoist (not shown) is connected to the
lifting eye 92 at the top of the lifting head 70. The
lifting head 70 is hoisted to expose the adapter pin 32,
the bottom end of which is then disconnected from the
tubing hanger 106. Thereafter, the entire well stimulation
tool 11 together with the high-pressure valve 64 is hoisted
onto a service truck (not shDwn).
After the well stimulation tool 11 with the
high-pressure valve 64 is removed, a wellhead (not shown)
is mounted to the tubing head spool 102. The wireline
lubricator 108 is then mounted to the top of the wellhead
and the wireline 110 is run into the production tubing
string to retrieve the plug 112. The well is then ready
for the production of hydrocarbons.
It should be noted that after the tubing hanger 106
is secured in the tubing head spool 102 in a well
completion, a blowout preventer that was required for the
well completion procedure may remain on the wellhead. It
should be understood, however, that the well stimulation
tool 10 or 11 in accordance with the invention can be used
with or without a blowout preventer in place.
FIG. 7 illustrates the well stimulation tool 11,
which is assembled with the high-pressure valve 64 and is
mounted on the top of a blowout preventer 120. The blowout
preventer 120 is mounted on the top of the tubing head
spool 102. In this case, either the adapter pin 32 or the
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mandrel 14 must be longer than that of a similar well
stimulation tool 11 used for a wellhead from which a
blowout preventer is removed, such as the embodiment
illustrated in FIGS. 2, 3, 5 and 6. In the embodiment
illustrated in FIG. 7, a longer adapter pin 32' replaces
the adapter pin 32 shown in FIGS . 2 , 3 , ~ 5 and 6 . The use
of the well stimulation tool 11 to stimulate a hydrocarbon
well to which a blowout preventer 120 shown in FIG. 7 is
mounted is similar to the procedure described with
reference to FIGS. 2, 3, 5 and 6, and is therefore not
redundantly described.
As will be understood by those skilled in the art,
the well stimulation tool 10 in accordance with the
invention can be used without the lifting head assembly.
In that case, the adapter spool 12, the mandrel 14 and the
adapter pin 32 are mounted to a top of the tubing head
spool 102 shown in FIG. 6, as described above. After they
are installed, a high-pressure valve 64 shown in FIG. 6 is
mounted to the top flange of the mandrel 14 and a
high-pressure line 114 shown in FIG. 6 is connected to a
top of the high-pressure valve 64. The high-pressure
flange 54 described above may also be used to connect the
high-pressure line to the high-pressure valve. It should
be further understood that the lockdown nut 30 shown in
FIG. 1 may include lift arms 94' (FIG. 2) with lift
eyes 96' to which cables are connected for hoisting the
well stimulation tool l0 into position over the wellhead,
or removing the well stimulation tool from the wellhead.
The embodiments of the invention described above
are therefore intended to be exemplary only. Consequently,
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the scope of the invention is intended to be limited only
by the scope of the appended claims.
