Note: Descriptions are shown in the official language in which they were submitted.
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FIXED-POINT PACKOFF ELEMENT WITH PRIMARY SEAL
TEST CAPABILITY
FIELD OF THE INVENTION
This invention relates in general to hydrocarbon well
stimulation equipment and, in particular, to a fixed-point
packoff element with primary seal test capability.
BACKGROUND OF THE INVENTION
The inventions of Assignee's pressure isolation tools that
provide full-bore access to a casing of the well have
revolutionized the well stimulation industry. Full-bore
isolation tools seal or "pack off" at a fixed-point above a
bit guide in a seal bore of a tubing head spool that
supports a production casing in the well, and permit full
bore access to the production casing.
A fixed-point packoff element provides a high pressure
seal in the tubing head spool seal bore. The full-bore
access pressure isolation tools permit stimulation fluid to
be pumped into a well at pressures of 15,000+ psi and rates
of 300+ bbl/minute. As well, the fixed-point packoff
element permits any downhole tool to be run into the casing
so that multiple production zones can be stimulated without
unrigging frac irons or the full-bore pressure isolation
tool.
Since stimulation fluids are commonly pumped into the
well at fluid pressures of at least 10,000 psi, the packoff
element must provide a very reliable high pressure seal. In
order to do so, the packoff element must have an outer
diameter that is not more than about 0.005"-0.030" smaller
than an inner diameter of the tubing head spool seal bore.
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As is well understood in the art, an exact inner diameter
of a tubing head spool seal bore is not always known with
certainty. Consequently, full-bore pressure isolation tools
have been rigged up as follows: a packoff element is
selected based on a best knowledge of an inner diameter of
the tubing head spool seal bore; the packoff element is run
it and set; frac irons are hooked up to the full-bore
pressure isolation tool and the well is pumped up to test
pressure; a tubing head spool side port is monitored for
pressure leaks; and, if the packoff element does not
contain the test pressure, the test pressure is bled off,
the frac irons are disconnected, the pressure isolation
tool is removed from the wellhead and the packoff element
is changed for a next larger diameter, typically about
0.015" larger. The entire process is then repeated. This
can be a time consuming and expensive process.
There therefore exists a need for a fixed-point
packoff element with a primary seal test capability to
permit primary seal testing prior to rigging up the
pressure isolation tool for a well stimulation operation.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide
a fixed-point packoff element with a primary seal test
capability.
The invention therefore provides a fixed-point packoff
element, comprising: at least one 0-ring groove adapted to
receive an 0-ring that provides a primary seal between the
fixed-point packoff element and a seal bore below a side
port of a tubing head spool into which the fixed-point
packoff is inserted; and at least one 0-ring groove adapted
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to receive an 0-ring that provides a test seal in a seal
bore of the tubing head spool above the side port of the
tubing head spool.
The invention further provides a fixed-point packoff
element for a high-pressure mandrel of a full-bore pressure
isolation tool, comprising: a hollow cylindrical body with
a top end and a bottom end and a central passage that
extends from the top end to the bottom end; at least one 0-
ring groove in an outer periphery of the hollow cylindrical
body, adapted to receive an 0-ring that provides a primary
seal between the fixed-point packoff element and a seal
bore below a side port of a tubing head spool into which
the fixed-point packoff is inserted; and at least one 0-
ring groove in the outer periphery of the hollow
cylindrical body, adapted to receive an 0-ring that
provides a test seal in a seal bore of the tubing head
spool above the side port of the tubing head spool.
The invention yet further provides a fixed-point
packoff element for a high-pressure mandrel of a full-bore
pressure isolation tool, comprising: a hollow cylindrical
body having a threaded top end for connection to a high-
pressure mandrel of the full-bore pressure isolation tool,
a bottom end with a bevel adapted to mate with a bit guide
in a tubing head spool, and a central passage that extends
from the top end to the bottom end in fluid communication
with the high-pressure mandrel; a plurality of 0-ring
grooves in an outer periphery of the hollow cylindrical
body, respectively adapted to receive an 0-ring that
provides a primary seal between the fixed-point packoff
element and a seal bore below a side port of a tubing head
spool into which the fixed-point packoff is inserted; and
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at least one 0-ring groove in the outer periphery of the
hollow cylindrical body, adapted to receive an 0-ring that
provides a test seal in a seal bore of the tubing head
spool above the side port of the tubing head spool.
BRIEF DESCRIPTION OF THE DRAWINGS
Having thus generally described the nature of the
invention, reference will now be made to the accompanying
drawings, in which:
FIG. 1 is a schematic cross-sectional diagram of one
embodiment of a fixed-point packoff element in accordance
with the invention;
FIG. 2 is a schematic cross-sectional diagram of
another embodiment of the fixed-point packoff element in
accordance with the invention;
FIG. 3 is a schematic cross-sectional diagram of the
fixed-point packoff element shown in FIG. 1 packed off in a
seal bore of a tubing head spool of a wellhead;
FIG. 3a is a schematic cross-sectional diagram of an
exploded view of the tubing head spool and fixed-point
packoff element shown in FIG. 3;
FIG. 4 is a schematic cross-sectional diagram of the
fixed-point packoff element shown in FIG. 2 packed off in a
seal bore of a tubing head spool of a wellhead; and
FIG. 4a is a schematic cross-sectional diagram of an
exploded view of the tubing head spool and the fixed-point
packoff element shown in FIG. 4.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention provides a fixed-point packoff element
for a full-bore pressure isolation tool that permits
primary seal testing to facilitate rig up for a well
stimulation procedure. The fixed-point packoff element
provides a secondary seal in the seal bore above side ports
of a tubing head spool. This permits test fluid to be
pumped through a side port of the tubing head spool to
determine whether a primary seal has been achieved. If the
fixed-point packoff element retains the test fluid, a
primary seal has been achieved and it can be assumed with a
high level of confidence that the fixed-point packoff
element will provide a reliable pressure seal at full well
stimulation fluid pressure.
FIG. 1 is a schematic cross-sectional diagram of one
embodiment of a fixed-point packoff element 10 in
accordance with the invention. The fixed-point packoff
element 10 is a hollow cylindrical body connected to a
high-pressure mandrel 12 of a full-bore pressure isolation
tool (not shown) that is well known in the art. A box
thread 14 of the high-pressure mandrel 12 cooperates with a
pin thread 16 of the fixed-point packoff element 10 to
connect the fixed-point packoff element 10 to the high-
pressure mandrel 12. An 0-ring groove 17 receives an 0-
ring 18 that provides a high-pressure seal between the
fixed-point packoff element 10 and the high-pressure
mandrel 12 to inhibit well stimulation fluids from
migrating into the threads 14, 16. At least one 0-ring
groove, three in this example, 15a, 15b and 15c
respectively receive 0-rings 20a, 20b and 20c to provide a
high-pressure primary seal in a seal bore of a tubing head
spool, as will be explained below with reference to FIGs. 3
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and 3a. An optional 0-ring groove 21 receives an 0-ring 22
that provides a fluid seal between a bit guide of the
tubing head spool and the fixed-point packoff element 10.
In this embodiment, a test fluid groove 24 is machined into
a periphery of the fixed-point packoff element 10. The
test fluid groove 24 is optional. At least one 0-ring
groove, in this example two 0-ring grooves 25a and 25b
respectively receive 0-rings 26a, 26b, that provide a test
seal above side ports of the tubing head spool, as will
also be explained below with reference to FIGs. 3 and 3a.
In this embodiment a top end 28 of the fixed-point
packoff element 10 provides a polished seal pin 30 that
seals against the 0-ring 18. As will be understood by
those skilled in the art, a seal bore could be provided in
the high-pressure mandrel 12 above the box thread 14, and
the 0-ring 18 could be carried in an 0-ring groove machined
in the top end 28 of the packoff element 10. In this
embodiment, a bottom end 32 of the packoff element 10 is
beveled 34 to mate with the bit guide of the tubing head
spool, as will also be explained below with reference to
FIG. 3a. As is apparent, a central passage 36 through the
fixed-point packoff element 10 has an inner diameter equal
to an inner diameter of a central passage 38 of the high-
pressure mandrel 12. The inner diameter of the central
passage 36 is at least as large as an inner diameter of a
production casing supported by a tubing head spool into
which the fixed-point packoff element is inserted.
FIG. 2 is a schematic cross-sectional diagram of
another embodiment of a fixed-point packoff element 50 in
accordance with the invention. The fixed packoff element
50 is substantially identical to the fixed packoff element
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described above except that the hollow cylindrical body
is designed for a tubing head spool in which the seal bore
above the bit guide is of a smaller diameter than a seal
bore above the side ports of the tubing head spool, as will
5 be explained below in more detail with reference to FIGs. 4
and 4a.
The fixed-point packoff element 50 is connected to the
box threads 14 by a pin thread 52. The top end 54 includes
a seal pin 56 that seals against the 0-ring 18, as
10 explained above with reference to FIG. 1. At least one 0-
ring groove, in this example 4 0-ring grooves 61a, 61b, 61c
and 61d respectively receive 0-rings 62a, 62b, 62c and 62d
that provide the primary seal. In this embodiment the
bottom end 58 includes a bevel 60 that mates with the bit
guide, as will be explained below with reference to FIG.
4a. An optional 0-ring groove 63 receives an 0-ring 64
that provides a seal between the bevel 60 and the bit guide
to inhibit well stimulation fluid from migrating between
the bevel 60 and the bit guide.
An optional test fluid groove 66 is machined around an
outer periphery of the fixed-point packoff element 50. A
test seal is provided by at least one 0-ring received in at
least one 0-ring groove. In this example, two 0-ring
grooves 65a and 65b respectively receive 0-rings 68a, 68b
that provide the test seal. A central passage 70 of the
fixed packoff element 50 has the same inner diameter as the
central passage 38 of the high-pressure mandrel 12. The
inner diameter of the central passage 70 is at least as
large as an inner diameter of a production casing supported
by a tubing head spool into which the fixed-point packoff
element is inserted. An outer diameter of the fixed-point
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packoff element 50 increases at a shoulder 72 to conform to
an inner diameter of the tubing head spool, as will be
explained below with reference to FIG. 4a.
FIG. 3 is a schematic cross-sectional diagram of the
fixed-point packoff element 10 shown in FIG. 1 packed off
in a seal bore of a tubing head spool 100 of a wellhead
102. The mandrel 12 of a full-bore isolation tool 104
(only a base of which is shown) has been stroked down
through a blowout preventer (BOP) 106 until the fixed-point
packoff element 10 rests against the bit guide of the
tubing head spool 100. The tubing head spool 100 shown in
this example has two side ports 108a, 108b. The side port
108a is sealed with the side port plug 110, well known in
the art. The side port 108b is equipped with the side port
valve 112, also well known in the art. A test fluid line
114 is connected to the side port 112 so that test fluid
can be pumped into the test fluid groove 24 to test the
primary seal of the fixed-point packoff element 10, as will
be explained below with reference to FIG. 3a.
FIG. 3a is a schematic cross-sectional diagram of an
exploded view of the fixed-point packoff element 10 shown
in FIG. 3. As can be seen, the bevel 34 on the bottom end
32 of the fixed-point packoff element 10 mates with a bit
guide 116 of the tubing head spool 100. The 0-rings 20a,
20b and 20c provide the primary seal between a seal bore
118 of the tubing head spool 100 and the fixed-point
packoff element 10. The 0-ring 22 provides a fluid seal
between the bevel 34 and the bit guide 116. As also
explained above, the test seal is provided by the 0-rings
26a and 26b. Test fluid 120 is injected through the test
fluid line 114 and the side port 112 to fill a space
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defined by the side port valve, the test groove 24 and a
space between a sidewall of the fixed-point packoff element
and the tubing head spool seal bore 118. The test fluid
may be any appropriate fluid, including hydraulic oil,
5 water, air, etc. After the space is filled, the test fluid
is pumped to a pressure at or near a rated pressure of the
side port valve 112. If the test fluid pressure is
maintained by the fixed-point packoff element 10, a primary
seal has been achieved and rig up can continue with a high
10 degree of confidence that the fixed-point packoff element
will provide a reliable seal at full well stimulation fluid
pressure.
If the primary seal is not achieved, either the
primary seal 0-rings 20a, 20b, 20c or the test seal 0-rings
26a, 26b have failed to seal against the seal bore 118.
Consequently, the mandrel 12 is stroked backup through the
BOP 106 and the full-bore pressure isolation tool 104 is
removed from the BOP 106, so that the fixed-point packoff
element 10 can be changed for one of a slightly larger
diameter. The new fixed-point packoff element 10 is then
stroked down through the BOP and landed against the bit
guide 116. The primary seal test is then repeated. All of
this is accomplished before frac irons or other well
stimulation equipment is connected to the full-bore
pressure isolation tool 104. Uncertainty is therefore
reduced and time is potentially saved.
FIG. 4 is a schematic cross-sectional diagram of the
fixed-point packoff element 50 shown in FIG. 2 packed off
in a seal bore of a tubing head spool 200 of a wellhead
202. The mandrel 12 of the full-bore pressure isolation
tool 104 (only the base of which is shown) has been stroked
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down through the BOP 106 until the fixed-point packoff
element 50 rests against the bit guide of the tubing head
spool 200. The tubing head spool 200 shown in this example
has two side ports 208a, 208b. The side port 208a is sealed
by a side port plug 210. The side port 208b is equipped
with a side port valve 212, also well known in the art. A
test pressure line 214 is connected to the side port 212 so
that test fluid can be pumped in to test the primary seal
of the fixed-point packoff element 50, as will be explained
below with reference to FIG. 4a.
FIG. 4a is a schematic cross-sectional diagram of an
exploded view of the fixed-point packoff element 50 shown
in FIG. 4. As can be seen, the bevel 60 on the bottom end
58 of the fixed-point packoff element 50 mates with a bit
guide 216 of the tubing head spool 200. The 0-rings 62a,
62b, 62c and 62d provide the primary seal between a seal
bore 218 of the tubing head spool 200 and the fixed-point
packoff element 50. The optional 0-ring 64 provides a fluid
seal between the bevel 60 and the bit guide 216. In this
embodiment, the seal bore is stepped at 220 to a larger
diameter, and the outer diameter of the fixed packoff
element 50 increases at the shoulder 72 to conform to an
inner diameter of the seal bore 222 of the tubing head
spool 200. The test seal is provided by the 0-rings 68a
and 68b which seal against the seal bore 222.
Test fluid 224 is injected through the test fluid line
214 and the side port valve 212 to fill a space defined by
the side port valve 212 and the sidewall of the fixed-point
packoff between 0-rings 62a and 68b. As explained above,
the test fluid may be any appropriate fluid, such as
hydraulic oil, water, air, etc. After the space is filled,
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the test fluid is pumped to a pressure at or near a rated
pressure of the side port valve 212. If the test pressure
is maintained by the fixed-point packoff element 50, a
primary seal has been obtained and rig up can continue with
a high degree of confidence that the fixed-point packoff
element will provide a reliable seal at full well
stimulation fluid pressure. As explained above, if the test
pressure is lost, the fixed-point packoff element 50 is
changed and the test seal is re-tested.
While two embodiments of the fixed-point packoff
element in accordance with the invention have been
described, it should be understood that those embodiments
are exemplary only.
The scope of the invention is therefore intended to be
limited solely by the scope of the appended claims.
