Note: Descriptions are shown in the official language in which they were submitted.
CA 02596019 2009-07-23
CASING MANDREL FOR FACILITATING WELL
COMPLETION, RE-COMPLETION OR WORKOVER
TECHNICAL FIELD
The present invention relates generally to wellhead
assemblies and, in particular, to a casing mandrel for
facilitating well completion, re-completion or workover
procedures on wells equipped with independent screwed
wellheads.
BACKGROUND OF THE INVENTION
Independent screwed wellheads are well known in the
art and classified by the American Petroleum Institute
(API). The independent screwed wellhead has independently
secured heads for each tubular string supported in the well
bore. Independent screwed wellheads are widely used for
production from low-pressure productions zones because they
are economical to construct and maintain.
It is well known in the art that low pressure wells
frequently require some form of stimulation to improve or
sustain production. Traditionally, such stimulation
procedures involved pumping high pressure fluids down the
casing to fracture production zones. The high pressure
fluids are often laden with proppants, such as bauxite
and/or sharp sand.
Applicant's Canadian patent 2,428,613 which issued on
October 25, 2005 describes casing mandrels for independent
screwed wellheads that are assembled using threaded unions.
However, certain customers prefer a flanged production
tree.
There therefore exists a need for a casing mandrel
that provides full-bore access to a casing in a well to be
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stimulated, while ensuring that vulnerable wellhead seals
are isolated from well stimulation pressures that exceed
engineered stress tolerances of the seals, while
accommodating a flanged production tree.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide
a casing mandrel that provides full-bore access to a casing
in a well to be stimulated, while ensuring that vulnerable
wellhead seals are isolated from well stimulation pressures
that exceed engineered stress tolerances of the seals.
The invention therefore provides a casing mandrel for
wells completed using an independent screwed wellhead,
comprising: a casing mandrel body having a bottom end
received in a casing bowl of the independent screwed
wellhead, an annular shoulder adapted for mating engagement
with a top flange of a casing bowl nut of the independent
screwed wellhead, an axial passage that extends from the
bottom end to a top end of the casing mandrel body, and a
seal bore at a top of the axial passage adapted to receive
a fixed-point packoff connected to a high pressure mandrel
of a pressure isolation tool that provides full-bore access
to a casing supported by the casing mandrel; and the casing
mandrel top end includes a pin thread that engages a box
thread of a tubing head to support the tubing head.
The invention further provides a casing mandrel for
wells completed using an independent screwed wellhead,
comprising: a casing mandrel body having an annular
shoulder adapted for mating engagement with a top flange of
a casing bowl nut of the independent screwed wellhead, an
outer contour below the annular shoulder that mates with a
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casing bowl of the independent screwed welihead, an axial
passage that extends from a casing mandrel bottom end to a
casing mandrel top end of the casing mandrel body, the
axial passage having a diameter at least as large as an
internal diameter of a casing that the casing mandrel
suspends in the well, and a seal bore at a top of the axial
passage, the seal bore having a larger diameter than the
axial passage and adapted to receive a fixed-point packoff
connected to a high pressure mandrel of a pressure
isolation tool; and the casing mandrel top end extends
above the annular shoulder and includes a pin thread
located above a top of the casing bowl nut when the casing
bowl nut secures the casing mandrel to the independent
screwed wellhead, the pin thread adapted to be engaged by a
box thread of a tubing head supported by the casing
mandrel.
The invention yet further provides a casing mandrel
for an independent screwed wellhead comprising: a bottom
end supported in a casing bowl of the independent screwed
wellhead, the bottom end including an annular shoulder
engaged by a casing bowl nut of the independent screwed
wellhead to secure the casing mandrel in the independent
screwed wellhead; a top end that extends above a top of the
casing bowl nut, the top end comprising a pin thread
adapted to support a tubing head, and a smooth cylindrical
seal surface above the pin thread engaged by elastomeric
seals received in seal grooves in the tubing head; an axial
passage that extends from the top end to the bottom end,
the axial passage including a seal bore at a top end
adapted to receive a fixed-point packoff connected to a
high-pressure mandrel of a pressure isolation tool that
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provides full-bore access to a casing supported by the
casing mandrel.
The invention still further provides a casing mandrel
and tubing head for an independent screwed wellhead,
wherein: the casing mandrel comprises a bottom end
supported in a casing bowl of the independent screwed
wellhead, the bottom end including an annular shoulder
engaged by a casing bowl nut of the independent screwed
wellhead to secure the casing mandrel in the independent
screwed wellhead, and a top end that extends above a top of
the casing bowl nut, the top end comprising a pin thread
and a smooth cylindrical seal surface above the pin thread;
and an axial passage that extends from the casing mandrel
top end to the casing mandrel bottom end, the axial passage
including a seal bore at a top end adapted to receive a
fixed-point packoff connected to a high-pressure mandrel of
a pressure isolation tool that provides full-bore access to
a casing suspended by the casing mandrel; and the tubing
head comprises a tubing mandrel bowl that is adapted to
support a tubing mandrel, tubing mandrel lockdown screws
adapted to lock the tubing mandrel in the tubing mandrel
bowl, a bottom end with a box thread that engages the pin
thread of the casing mandrel to lock the tubing head to the
casing mandrel, and seal ring grooves located above the box
thread that support elastomeric seal rings which engage the
smooth cylindrical seal surface of the casing mandrel to
provide a fluid seal between the tubing head and the casing
mandrel.
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BRIEF DESCRIPTION OF THE DRAWINGS
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 schematic cross-sectional view of an
independent screwed wellhead equipped with a casing mandrel
in accordance with another embodiment of the invention;
FIG. 2 is a schematic cross-sectional view of a fixed-
point packoff being inserted into the casing mandrel of the
independent screwed wellhead shown in FIG. 1;
FIG. 3 is a schematic cross-sectional view of the
fixed-point packoff after it has been packed off in the
casing mandrel of the independent screwed wellhead shown in
FIG. 1;
FIG. 4 is a schematic cross-sectional view of the
fixed-point packoff being inserted into the casing mandrel
through a well control stack; and
FIG. 5 is a schematic cross-sectional view of the
fixed-point packoff being inserted into the casing mandrel
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 EMBODIMENT
The invention provides a casing mandrel to facilitate
and improve the efficiency of completing, re-completing or
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workover of wells equipped with independent screwed
wellheads. Efficiency is improved by providing full-bore
access to a casing of the well. Safety is improved by
ensuring that wellhead seals are isolated from well
stimulation pressures that exceed engineered stress
tolerances of the seals.
FIG. 1 is a schematic cross-sectional view of a casing
mandrel in accordance with one embodiment of the invention.
The casing mandrel 300 is received in the casing bowl 302
of an independent screwed wellhead 304 mounted to a surface
casing 306 in a manner well known in the art. The casing
mandrel 300 has an axial passage 310 with an inner diameter
at least as large as an inner diameter of a production
casing 312 that the casing mandrel 300 supports in a well
bore. A box thread 314 at a bottom end of the axial
passage 310 engages a pin thread 316 on the top of the
production casing 312 to suspend the production casing 312
in the well bore. Located at a top of the axial passage
310 is a seal bore 320 sized and shaped to receive a fixed-
point packoff connected to a high-pressure mandrel of a
pressure isolation tool, as will be explained below in
detail with reference to FIGs. 2-5. A top end of the
casing mandrel 300 as a beveled shoulder 322 that guides
downhole tools into the seal bore 320. A bevel 324 at a
bottom of the seal bore 320 guides downhole tools into the
axial passage 310.
The bottom end of the casing mandrel 300 received in
the tubing bowl 302 includes an upper cylindrical section
326 with 0-ring grooves 328, 330 that respectively receive
0-rings 332, 334 for providing a fluid seal between the
casing mandrel 300 and the independent screwed wellhead
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304. The bottom end of the casing mandrel 300 further
includes a tapered section 336 that supports the casing
mandrel 300 in the casing bowl 302. In one embodiment, the
tapered section 336 is tapered at an angle of about 45 .
Located above the bottom end of the casing mandrel 300
is an annular shoulder 338 engaged by a casing bowl nut 340
of the independent screwed wellhead 304. Casing bowl nut
340 secures the casing mandrel 300 in the casing bowl 302.
Located above a top of the casing bowl nut 340 on an outer
periphery of the casing mandrel 300 is a pin thread 342
engaged by a box thread 344 at a bottom end of a tubing
head 350, which is also supported by the casing mandrel
300. Located above the pin thread 342 is a smooth outer
cylindrical seal surface 346 of the casing mandrel 300.
Located below the pin thread is a second annular shoulder
348 that provides a support for a bottom end 366 of the
tubing head 350, to relieve strain on the pin thread 342
and the box thread 344. Seal ring grooves 352 and 354
located above the box thread 344 support elastomeric seal
rings that provide a fluid seal between the tubing head 350
and the casing mandrel 300. In this embodiment, the
elastomeric seals are 0-rings 356, 358 respectively
received in the seal ring grooves 352 and 354. The tubing
head 350 includes a tubing mandrel bowl 360 that supports a
tubing mandrel (not shown) in a manner well known in the
art. Tubing mandrel lockdown screws, two of which 362, 364
are shown, lock the tubing mandrel in the tubing mandrel
bowl 360.
FIG. 2 is a schematic cross-sectional view of a fixed-
point packoff secured to the bottom end of a high pressure
mandrel of a pressure isolation tool (not shown) being
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inserted into the casing mandrel 300 of the independent
screwed wellhead 304 shown in FIG. 1. As will be explained
below in more detail with reference to FIGs. 4 and 5 and as
well understood by those skilled in the art, the high
pressure mandrel 450 with the fixed-point packoff 400 is
normally inserted into the independent screwed wellhead
through a well control mechanism, which for example may be
one of: a frac stack; at least one high pressure valve; or,
a blowout preventer. The fixed-point packoff 400 is
threadedly connected to a bottom end of the high-pressure
mandrel 450. A plurality of elastomeric seal ring grooves
402-408 in an outer periphery of the fixed-point packoff
400 support elastomeric seals 410-416 to provide a high-
pressure fluid seal between the seal bore 320 and the
fixed-point packoff 400, as shown in FIG. 3. In one
embodiment, the elastomeric seals 410-416 are high-pressure
0-ring seals capable of containing fluid pressures of up to
at least 10,000 psi.
FIG. 3 is a schematic cross-sectional view of the
fixed-point packoff 400 after it has been inserted into the
seal bore 320 of the casing mandrel 300 shown in FIG. 1. As
explained above, the 0-rings 410, 412, 414 and 416 provide
a high pressure fluid seal in the seal bore 320 that
prevents high pressure well stimulation fluids pumped
through the high-pressure mandrel 450 into the production
casing 312 from migrating upward into the low-pressure
rated tubing head 350 and the elastomeric seals 356 and
358, as well as any low-pressure rated equipment mounted to
the tubing head 350.
FIG. 4 is a schematic cross-sectional view of the
fixed-point packoff 400 being inserted into the casing
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mandrel 320 through a frac stack 500. As is well known in
the art, the frac stack 500 commonly includes a first high-
pressure valve 502 that is mounted to a top of the tubing
head 350. Mounted to a top flange of the high-pressure
valve 502 is a cross-flow tee 504, generally used for flow-
back after a well stimulation procedure. The cross-flow tee
504 includes a pair of side ports to which are respectively
connected redundant control valves 506a, 506b and 506c,
506d. Connected to the outermost control valves 506a and
506d are connectors 508, 512 used to connect any one or
more of: flow-back lines; a pressure balance line; drain
pit lines; or the like. Mounted to a top of the cross-flow
tee is a second high-pressure valve 514. Mounted to a top
flange of the high pressure valve 514 is a pressure
isolation tool 600 that is schematically illustrated. The
pressure isolation tool 600 may be any tool/insertion
system that can be used to insert the high pressure mandrel
450 with the fixed-point packoff 400 down through the frac
stack 500 and into the casing mandrel seal bore 320.
Examples of suitable pressure isolation tools 600 include,
but are not limited to, tools described in Assignee's
United States patents: 6,817,423 which issued on November
16, 2004; 6,817,421 which issued on November 16, 2004;
6,626,245 which issued on September 30, 2003; 6,364,024
which issued on April 2, 2004; 6,289,993 which issued on
September 18, 2001; 6,179,053 which issued January 30,
2001; and 5,825,852 which issued February 15, 1994.
FIG. 5 is a schematic cross-sectional view of the
fixed-point packoff being inserted into the casing mandrel
through a blowout preventer (BOP) 700, which is also well
known in the art. The BOP 700 is mounted to a top of the
tubing head 350 and used to control well pressure before
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the high-pressure mandrel 450 with the fixed-point packoff
400 of the pressure isolation tool 600 is stroked into the
seal bore 320 of the casing mandrel 300. The BOP 700 also
controls well pressure after the high-pressure mandrel 450
with the fixed-point packoff 400 of the pressure isolation
tool 600 is stroked up out of the screwed independent
wellhead. As is well known in the art, the BOP 700 includes
at least one set of tubing rams 702 and at least one set of
blind rams 704.
As will be understood by those skilled in the art,
well completion is exemplary of only one procedure that can
be practiced using the methods and apparatus in accordance
with the invention. The method and apparatus in accordance
with the invention can likewise be used for well re-
completion, well stimulation, and any other downhole
procedure that requires full-bore access to the production
casing and/or production tubing of the well.
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.
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