Note: Descriptions are shown in the official language in which they were submitted.
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WELLHEAD AND CONTROL STACK PRESSURE TEST PLUG
TOOL
TECHNICAL FIELD
The invention relates generally to pressure-testing
tools for pressure control stacks on wellheads and, in
particular, to test plug tools for pressure-testing of
those control stacks.
BACKGROUND OF THE INVENTION
Prior art pressure-test plug tools far testing the
pressure integrity of pressure control stacks on wellheads
are well known in the art. The pressure-test plug tools
are used to test the pressure integrity of control stack
components such as blowout preventers, valves, tees, etc.,
and joints between the components prior to drilling or
stimulating a well.
While most prior art test plug tools are known to
function well, they all suffer from a drawback in ,that they
are only designed to test the pressure integrity of the
stack above a casing joint, i.e., above a connection
between a casing and a casing support. With prior-art
devices, the pressure integrity of the casing joint cannot
be verified. During well stimulation operations, where
fluid pressures may spike to 20,000 PSI, this joint may be
susceptible to leakage and/or failure, resulting in
expensive repairs, cleanup, downtime and potential
environmental damage.
Many configurations for pressure-test plug tools
have been invented. For example, in U.S. Patent 5,775,422
(along et a1.) entitled TREE TEST PLUG, the test plug is
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lodged within the tubing hanger, i.e., above the connection
between the surface casing and the wellhead. In this
configuration, the pressure integrity of the stack beneath
the tubing hanger cannot be verified.
In U.S. Patent 4,121,660 (Ko.leilat) entitled WELL
PRESSURE TEST PLUG, the test plug is seated in the bore of
the wellhead. With the test plug in this configuration,
the pressure integrity of the wellhead-to-casing joint
cannot be tested.
Similarly, in U.S. Patent 4,018,276 (Bode) entitled
BLOWOUT PREVENTER TESTING APPARATUS, the test plug is
positioned in the bore of the wellhead. The position of
the test plug permits pressure-testing of the blowout
preventer but does not permit pressure-testing of the
wellhead or the casing connection.
Likewise, in U.S. Patent 3,897,824 (Fisher)
entitled BLOWOUT PREVENTER TESTING APPARATUS, the test plug
is positioned in the bore of the wellhead beneath the
blowout preventer. With the test plug in this location, it
is not possible to verify the pressure integrity of the
lower part of the wellhead, such as the joint between the
wellhead and the well casing.
In U.S. Patent 3,177,703 (Waters et a1.) entitled
METHOD AND APPARATUS FOR RUNNING AND TESTING AN ASSEMBLY
FOR SEALING BETWEEN CONDUITS, the test plug is positioned
in the bore of the wellhead above the joint between the
wellhead and the casing. With the\ test plug in this
location, it is not possible to pressure-test the wellhead-
casing joint.
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In U.S. Patent 2,951,363 (Diodene) entitled TOOL
FOR TESTING WELL HEAD EQUIPMENT, the test plug is also
positioned above the wellhead and casing joint. Pressure-
testi.ng of the casing joint is not possible with the test
plug located in that position.
There therefore exists a need for a test plug tool
for pressure-testing wellhead control stacks that permits
testing of the pressure integrity of a casing joint, i.e.,
the joint between a surface casing and a wellhead, the
joint between an intermediate casing and an intermediate
casing mandrel, or the joint between a production casing
and a production casing mandrel.
SUI~?ARY OF THE INVENTION
It is therefore an object of the invention to
provide a test plug tool for use in testing the pressure
integrity of a pressure control stack mounted to a
wellhead, together defining a wellhead stack assembly,
including testing the pressure integrity of a joint between
a casing and a casing support that secures the casing to
the wellhead stack assembly, the test plug tool providing a
fluid-tight seal with the casing beneath the joint between
the casing and the casing support.
By constructing test plugs of appropriate
diameters, the test plug tool may be used for testing the
pressure integrity of a variety of casing joints, including
the joint between a surface casing and a wellhead, the
joint between an intermediate casing and an intermediate
casing mandrel, and the joint between a production casing
and a production casing mandrel.
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Preferably, the test plug tool includes a test plug
hanger and a test plug, the test plug being positioned
below the casing joint.
Preferably, the test plug of the test plug tool
comprises a cup tool with flange supporting a gauge ring, a
sealing element and a cup for providing a fluid-tight seal
between the test plug and the casing.
The invention further provides a method for testing
the pressure integrity of seals and joints in a pressure
control stack mounted on a wellhead, together defining a
wellhead stack assembly, including testing the pressure
integrity of a joint between a casing and a casing support,
the method comprising the steps of inserting a test plug
tool into the wellhead stack assembly with a landing tool;
landing the test plug in the casing beneath the joint
between the casing and the casing support; locking the test
plug tool in position; detaching the landing tool from the
test plug tool; retracting the landing tool from the
wellhead stack assembly; pressurizing the wellhead stack
assembly to an estimated operating pressure; and inspecting
the seals and joints of the wellhead stack assembly,
including the joint between the casing and the casing
support, to ascertain that the seals and joints have
withstood the estimated operating pressure.
The method can be applied to the testing of various
casing joints, including the joint between a surface casing
and a wellhead, the joint between an intermediate casing
and an intermediate casing mandrel, and the joint between a
production casing and a production casing mandrel.
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BRIEF DESCRIPTION OF THE DRAWINGS
Further features and advantages of the 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 wellhead with
a control stack attached thereto and showing a test plug
tool in accordance with the invention with the test plug
landed in the surface casing beneath the joint between the
surface casing and the wellhead;
FIG. 2a is a cross-sectional view of the wellhead,
control stack and test plug tool shown in of FIG. 1,
illustrating a landing tool connected to the test plug tool
for inserting the test plug tool into the control stack and
wellhead;
FIG. 2 is a cross-sectional view of a wellhead with
a control stack attached thereto and showing a test plug
tool in accordance. with the inventp_on with the test plug
landed in the intermediate casing beneath the joint between
the intermediate casing and the intermediate casing
mandrel;
FIG. 3 is a cross-sectional view of a wellhead with
a control stack attached thereto and showing a test plug
tool in accordance with the invention with the test plug
landed in the production casing beneath the joint between
the production casing and the production casing mandrel:
FIG. 4 is a cross-sectional view of a wellhead with
a control stack attached thereto and showing a test plug
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tool equipped with a backpressure valve in accordance with
a further embodiment of the invention;
FIG. 5 is a cross-sectional view of a wellhead with
a control stack attached thereto and showing a test plug
tool equipped with another embodiment of a backpressure
valve in accordance with the invention;
FIG. 6 is a cross-sectional view of the
backpressure valve shown in FIG. 5; and
FIG. 7 is a cross-sectional view of an upper
portion of a wellhead with a pressurized control stack
attached thereto and showing a test plug tool with a
backpressure valve in accordance with an embodiment of the
invention.
It will be noted that throughout the appended
drawings, like features are identified by like reference
numerals.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In general, and as will be explained below, a test
plug tool can be used for testing the pressure integrity of
a welihead having a pressure control stack mounted thereto.
The wellhead and the pressure control stack will be
referred to hereinafter as a "wellhead stack assembly".
The test plug of the test plug tool is designed to be
landed below a casing joint formed between a casing and a
casing support so that this casing joint and all joints
above it in the pressure control stack can be pressure-
tested. The expression "casing joint" as used in this
specification means a joint between a casing and a casing
support. A "casing", as persons skilled in the art will
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understand, includes a surface casing, an intermediate
casing and a production casing. A "casing support" means a
component of the wellhead stack assembly that holds and/or
secures the casing to the wellhead stack assembly, and
suspends the casing in a well bore. Bersons skilled in the
art will understand that where the casing is surface
casing, the casing support is typically a wellhead. Where
the casing is an intermediate casing, the casing support is
generally an intermediate casing mandrel. Where the casing
is production casing, the casing support is generally a
production casing mandrel.
By constructing test plugs of suitable diameter,
the test plug tool can be used to pressure-test the surface
casing, the intermediate casing or the production casing.
The test plug tool includes a test plug hanger with fluid
passages to permit test fluids to pass therethrough, a test
plug leg that extends downwardly from the test plug hanger
to support a test plug. In one embodiment, the test plug
is a cup tool that includes a cup sleeve which terminates
in a bullnose, the cup sleeve supports, above an annular
abutment, a gauge ring, an elastomeric sealing element and
an elastomeric cup. The gauge ring, sealing element and
cup are dimensTOned to provide a high-pressure fluid seal
against an inside of the casing. During operation, the
valves of the pressure control stack are closed, the side
ports are plugged and the stack is pressurized to at least
an estimated operating pressure to verify that all seals
and joints, including the casing joint, are able to
withstand the estimated operating pressure.
FIG. 1 illustrates what is known in the art as a
pressure control stack 10 [hereinafter the "stack"] which
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is configured for pressure integrity testing. The
expression "pressure integrity testing" as used in this
specification means a testing procedure during which the
stack is pressurized to at least an estimated operating
pressure and the joints and seals are inspected to Verify
that they have withstood the test. pressure.
At the base of the stack 10, and dug into the
ground 12, is a conductor 14. The conductor 14 is
installed, or "stuffed", into a "rat-hole" that is
typically bored 60 to 80 feet deep, depending on subsurface
conditions. The conductor 14 supports a conductor ring 16
on the upper lip of the conductor. The conductor ring 16
is beveled to form a bowl-shaped receptacle 18 for
receiving a bottom beveled portion of a wellhead 22. A
surface casing 20 is connected to the wellhead 22 below the
side ports 24 of the wellhead. 'The side ports 24 are
sealed during pressure-testing.
The surface casing 20 is joined to the wellhead 22
at a wellhead-to-casing joint 26. The wellhead-to-casing
joint 26 is formed between an upper portion of the surface
casing 20 and a lower portion of the wellhead 22, as
illustrated in FIG. 1.
As shown in FIG. 1, mounted atop the wellhead 22 is
a drilling flange 30 which is secured to an upper portion
of the wellhead 22 by a wing n.ut 32. The drilling
flange 30 has transverse bores in a flanged portion 34 that
house locking pins 36. Each locking pin has a head 38.
Mounted atop the drilling flange 30 is a blowout
preventer 40, well known in the art.
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Before the stack is pressurized, a test plug
tool 50 is inserted into the bore of the stack 10. The
test plug tool 50 includes a test plug hanger 51 and a test
plug 53 which are interconnected by a test plug leg 58.
The,test plug hanger 51 of the test plug tool 50
includes a landing joint connector, which is a box threaded
socket 52 for receiving one of a pin threaded landing
joint 150 as illustrated in FIG. 1a, a drill pipe, or a
production tubing. In operation, the drill pipe, the
production tubing or the landing tool 150 is threaded to
the socket 52 and then the test plug tool 50 is lowered
into the stack 10 and the test plug is landed inside the
casing, as shown in FIG, la.
The test plug hanger 51 includes a hanger flange 54
that extends laterally from the socket 52 to an outer
radius of the test plug hanger 51. The annular shoulder 54
has a beveled top edge that is locked in place by the
locking pins 36, so that the test plug hanger 51 is
restrained from upward movement. In addition, the bottom
surface of the hanger flange 54 rests on an annular
abutment 31 in the drilling flange 30, which prevents the
test plug hanger 51 from moving downwardly through the
wellhead contro l stack. Since the hanger flange 54 is
locked between the annular abutment 31 and the heads 38 of
the locking pins 36, the test plug 'tool 50 cannot be
displaced during pressurization of the stack 10.
The hanger flange 54 also includes at least one
fluid passage 56 that are extends through the test plug
hanger. During pressurization of the stack, pressurized
fluid flows through the fluid passage 56. The fluid
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passage 56 thus permits pressure to equalize on both sides
of the hanger flange 54.
The test plug tool 50 has a test plug leg 58
integrally formed with the hanger flange 54 and extending
downwardly from the underside of the hanger flange 54 to a
test plug 53. A bottom end 59 of the test plug leg 58 is
threaded to an upper end 61 of a cup tool 60. The test
plug leg 58 is preferably hollow to reduce a weight of the
test plug tool 50. As illustrated in FIG. l, the cup
tool 60 includes a bullnose 60a at the bottom and a cup
sleeve 6Ob with an outer diameter less than that of the
bullnose 60a. Because the bullnose 60a has a greater outer
diameter than that of the cup sleeve 60b, the top surface
of the bullnose 60a forms an annular shoulder 60c. The
annular shoulder 60c extends in the radial direction but
does not contact the surface casing 20. A small annular
gap 60d remains between the annular shoulder 60c and the
surface casing 20.
Supported directly above the annular shoulder 60c
is a metal gauge ring 62. The gauge ring 62 is dimensioned
to support an elastomeric sealing element 64 and to inhibit
the elastomeric sealing element 64 from extruding between
the casing and the bullnose 60c when the test plug tool 50
is exposed to elevated fluid pressures. The elastomeric
sealing element 64 forms a fluid seal with the surface
casing 20 when compressed by an elastomeric cup 66 that is
supported directly above the elastomeric sealing
element 64. The elastomeric cup 66 is preferably made of
nitrite rubber, although persons skilled in the art will
appreciate that other elastomers or polymers, such as
polyethylene or polystyrene, may also be used. The
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elastomeric cup 66 is also dimensioned to form a fluid seal
against the surface casing 20. The elastomeric cup 66 is
bonded to a steel ring that slides over the cup sleeve 60b.
The steel ring .includes a pair of radial grooves for
seating two O-rings 68. The 0-rings 68 provide a fluid
seal between the elastomeric cup 66 and the cup sleeve 60b.
During pressure-testing, pressurized fluid flows
through the fluid passages 56 in the test plug hanger 51 to
pressurize an annular space 55. The annular space 55 is a
generally annular volume defined between the test plug
leg 58 and the stack 10. The annular space is pressurized
to at least an estimated operating pressure, which may be
as high as 20,000 PSI (or about 140 MPa). Since the cup 66
is below the wellhead-to-casing faint 26, this joint is
subjected to the test pressure. Thus, with the test plug
tool 50, it is possible to test the pressure integrity of
the wellhead-to-casing joint 26.
As illustrated in FIG. 2, the test plug 50 can be
designed and constructed with a smaller outer diameter for
use in testing the pressure integrity of a stack 10
configured with an intermediate casing 70 in addition to
the surface casing 20. As is known by persons skilled in
the art, industry regulations in certain jurisdictions
require that intermediate casing be run into the well as a
safety measure when exploiting a deep, high-pressure well.
As shown in FIG. 2, the wellhead 22 is seated on
the bowl-shaped receptacle 18 of the conductor ring 16
which, in turn, is mounted on the conducto r 14. The
surface casing 20 is joined to the wellhead 22 below the
side ports 24 at a wellhead-to-surface casing joint 26.
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(These components are configured in the same way as those
shown in FIG. 1.)
The wellhead 22 supports an intermediate casing
mandrel 72 which is threadedly fastened to the intermediate
casing 70 to form a joint with a frusta-conical interface
which will be referred to below as an intermediate casing-
to-mandrel joint 75.
The drilling flange 30 is secured to an upper
end 88 of an intermediate head spool 80 by the wing nut 32.
The drilling flange 30 includes lockdown pins 36 in the
upper flanged portion 34. A blowout preventer 40 is
mounted to the upper flanged portion 34, as described
above.
The test plug tool 50 is inserted with a landing
tool 150 (shown in FIG. 1a) which connects to the box
threaded socket 52. The test plug tool 50 is inserted into
the stack 10 and positioned at the location shown in
FIG. 2, such that the test plug 53 is beneath the
intermediate casing-to-mandrel joint 75. The test plug 53
shown in FIG. 2 has a smaller outer diameter than the test
plug shown in FIG. 1. To ensure a fluid-tight seal, the
cup tool 60, the gauge ring 62, the sealing element 64 and
the cup 66 are constructed with diameters appropriate for
the size and weight of the intermediate casing, as is
understood by persons skilled in the art.
The test plug hanger 5I is secured in place by the
locking pins 36 in the upper flanged portion 34 of the
drilling flange 30, as already explained above. The
heads 38 of the locking pins 36 engage the annular
shoulder 54 of the test plug hanger 51 to prevent the test
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plug from moving upward during pressurization. As also
explained above, the fluid passages 56 serve to equilibrate
pressure on each side of the test plug hanger 51 during
pressurization of the annular space 55.
As illustrated in FIG. 2, because the test plug
tool 50 may be inserted beneath the intermediate casing-to
mandrel joint 75, this joint (and all the joints and seals
above it in the stack) may be pressure-tested to ensure
that they are able to withstand at least the estimated
operating pressure.
FIG. 3 illustrates another embodiment of the test
plug tool 50' which is designed to be used in testing the
pressure integrity of a production casing 90 which is run
inside an intermediate casing 70 for drop well production.
As illustrated, the test plug 53' of the test plug
tool 50.' resembles the test plug 53 of the test plug
tool 50 except that the test plug 53' has a solid cup
sleeve 60b', whereas the test plug 53 has tubular cup
sleeve 60b. The reason for this design is explained below.
Other than the solid cup sleeve 60b', the test plug 53'
resembles the test plug 53 in that the cup tool 60' which
supports a metal gauge ring 62', a sealing element 64' and
an elastomeric cup 66', each of which have a smaller outer
diameter than the outer diameter of the test plug of
FIG. 2, so as to fit the smaller bore of the production
casing 90. The test plug 50' also has 0-rings 68' to
provide a fluid seal between a steel ring that supports the
elastomeric cup 60b of the cup tool 60.
The production casing 90 is fastened to a
production casing mandrel 92 to form a production casing-
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to-mandrel joint 95. A flared bottom portion of the
production casing mandrel 92 is seated in a bowl-shaped
portion 94 of the intermediate spool 80. The intermediate
spool 80 is secured to the wellhead 22 by a wing nut 32 as
described above with reference to FIG. 2.
A tubing head spool 100 is mounted to a top of the
intermediate spool 80. The tubing head spool 100 includes
flanged side ports 114 and further includes a top
flange 116 which has transverse bores for housing locking
pins 118 for securing a tubing mandrel (commonly referred
to as a tubing hanger or a "dognut'°). A flanged Bowen
union 120 is mounted to a top of the top flange 116. The
flanged Bowen union 120 has a box threaded socket 124 for
receiving a pin threaded upper end 50a of the test plug
tool 50. The flanged Bowen union 120 also has a pair of
annular grooves 125 for seating 0-:rings for providing a
fluid-tight seal between the upper end of the test plug and
the flanged Bowen union 120. The flanged Bowen union 120
has at its uppermost end a threaded union 126, a type of
connection that is well know in the art for connecting
high-pressure lines, or the like. The flanged Bowen
union 120 includes an axial passage 127.
The test plug 50' has a differently shaped test
plug hanger 51' than the test plug hanger 51 of the
embodiment shown in FIGS. 1 and 2. The test plug
hanger 51' shown in FIG. 3 includes a hanger flange 54'
with beveled shoulders dimensioned to fit snugly in the
bore of the tubing head spool 100. The lower beveled
shoulder is machined to rest against a bowl-shaped abutment
in the tubing head spool 100, which prevents the test
plug 50' from descending further into the wellhead stack
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assembly. Three peripheral grooves 57 are machined into
the hanger flange 54'. Three 0-rings are seated in the
grooves 57 to provide a fluid-tight seal between the test
plug hanger 51' and the tubing head spool 100, because the
tubing head spool 100 above the tubing hanger bowl is
normally not subjected to elevated fluid pressure and the
tubing head spool 100 is not necessarily constructed to
withstand high fluid pressures.
A fluid passage 58a is machined through a sidewall
of the test plug leg 58 to permit pressurized fluid to flow
through the central bore 127 of the flanged Bowen
union 120, through the fluid passage in the sidewall of the
test plug hanger 51' and into the annular space 55, i.e.,
the annulus between the test plug leg 58 and the wellhead
stack assembly l0. Since pressurized fluid flows below the
production casing mandrel joint 95, this joint can be
pressure-tested.
In summary, the test plug tools 50, 50' shown in
FIGS. 1, 2 and 3 may be dimensioned for use in testing the
pressure integrity of pressure control stacks attached to
wellheads. As described and illustrated above, the test
plug tools may be used to test the pressure integrity of
the wellhead-to-surface casing joint (FIG. 1), the
intermediate casing mandrel joint (FIG. 2), and the
production casing mandrel joiht (FIG. 3). In each of these
three applications, the test plug tool is also useful for
testing the various joints and seals above the wellhead
surface casing joint, the intermediate casing mandrel
joint, or the production casing mandrel joint, as the case
may be, including the rams of blowout preventer(s) located
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above the wellhead stacks, and any control valves mounted
to the wellhead stack 10.
As shown ;~n FIG. 4, the test plug tool 50 may
further include a backpressure valve 200 which communicates
with an axial passageway 220 in the test plug hanger 51.
The backpressure valve is a one-way valve used to ensure
that a fluid-tight seal is provided by the test plug tool.
If the test plug tool fails to provide a fluid-tight seal,
pressurized fluid can leak past the test plug 53, causing
backpressure to build up downhole of the test plug tool.
Such downhole backpressure may damage the casing or cause
other problems.
As shown in FIG. 4, the backpressure valve 200 is a
generally annular body 202 with pin threads for engaging a
box thread in a test plug hanger 51. The backpressure
valve 200 also has a spring-loaded ball valve, which
includes a ball 216 that is forced downwardly against an
annular shoulder by a spring 218. The spring is retained
by an annular retainer cap 224 that threads onto the
annular body 202. The structure of the backpressure valve
will be described in greater detail below with regard to
FIG. 6. In operation, if the test plug tool leaks and
backpressure builds up beneath the test plug 53,
pressurized fluid will travel up a central bore 50b of the
test plug tool 50 and up the axial passageway 220. If the
backpressure is more than a few paunds per square inch
(PSI), the spring-loaded ball valve will be displaced
upwardly against the spring, thereby permitting pressurized
fluid to flow up a central bore of the landing tool 150,
thereby alerting an operator of the leak.
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FIG. 5 illustrates another embodiment in which the
test plug tool 50 employs another embodiment of a
backpressure valve 200, the structure of which is
illustrated in greater detail in FIG. 6. The backpressure
valve 200 shown in FIG. 6 also has a spring-loaded ball
valve which is displaced upwardly when the backpressure
exceeds the compressive resistance of the spring.
As shown in FIG. 6, the backpressure valve 200
includes a generally annular body 202 which has threads 203
for connecting to an annular anchor that in turn threadedly
engages (via threads 208) to the test plug hanger 5l. A
gasket 210 sits in an annular groove to provide a fluid-
tight seal between the test plug hanger 51 and a lower
portion 206 of the annular anchor 204.
The backpressure valve includes a ball 216 which is
forced downwardly by a compression spring -218 against an
annular gasket 214 which sits on annular shoulder of the
anchor 204. The annular shoulder defines an aperture
through which pressurized fluid may flow. In other words,
the backpressure valve is a one-way spring-loaded ball
valve in which the spring exerts a downward force on the
ball for obstructing the aperture defined by the annular
shoulder.
In operation, if a leak occurs and the backpressure
exceeds the compressive resistance of the spring, then the
ball is displaced upwardly, thereby permitting pressurized
fluid to flow from the axial passageway 220 to an upper
passageway 222 and upwards through a central bore 151 of
the landing tool 150.
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Depicted in FIG. 7 is a set-up for pressurizing the
wellhead and control stack. The test plug tool 50 is
inserted into the stack using the landing tool 150 and is
locked into place by locking pins 36 in the drilling
flange 30. Mounted atop the drilling flange 30 is the
blowout preventer 40. Secured. atop the blowout
preventer 40 is the tubing head spool 100 having flanged
side ports 102 for injection of pressurized fluids for
testing the pressure integrity of the wellhead and stack.
Secured atop the tubing head spool 100 is a tubing
adapter 250. The tubing adapter 250 is flanged to the
tubing head spool and is sealed thereto with a ring gasket
which is housed in an annular groove 252. The tubing
adapter 250 has threads 255 for connection to a retainer
nut 260. The tubing adapter also has a radially inward
annular cavity known as a stuffing box. The stuffing box
houses a packing L~etainer ring 262, a chevron packing 264
and a packing nut 266. Accordingly, with the stack
configured as shown in FIG. 7, the annular space 55 can be
pressurized to test the pressure integrity of the wellhead
and stack. If pressurized fluid leaks past the test plug,
backpressure will force open the backpressure valve 200,
thereby permitting fluid to flow up the central bore 151 of
the landing tool 150.
Persons skilled in the art will appreciate that
these test plug tools may be modified to suit similar
pressure-testing applications. The embodiments of the
invention described above are therefore intended to be
exemplary only. The scope of the invention is intended to
be limited solely by the scope of the appended claims.
