Note: Descriptions are shown in the official language in which they were submitted.
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EROSION RESISTANT FRAC HEAD
FIELD OF THE INVENTION
[0001] This invention relates in general to hydrocarbon well
stimulation equipment and, in particular, to an erosion
resistant frac head.
BACKGROUND OF THE INVENTION
[0002] Current methods for completing or re-completing
hydrocarbon wells may involve pumping very large volumes of
propant into one or more production zones of the well. More
than 10,000,000 pounds (4,555,000 kg) of propant (e.g.,
frac sand, sintered bauxite, or ceramic pellets) mixed with
a fracturing fluid such as "slick water" may be pumped
through a frac head and down a production casing into
production zone(s) of the hydrocarbon well at rates of 300+
bbl/minute during a well stimulation procedure. As
understood by those skilled in the art, pumping millions of
pounds of abrasive propant through known frac heads at high
rates causes erosion, commonly referred to as "wash", in
those frac heads.
[0003] The construction and maintenance of frac heads
requires skilled labor and expensive alloy steel (e.g. 4140
steel). In order to reduce the cost of maintaining frac
heads, abrasion-resistant frac heads with hardened steel
inserts were invented, as taught for example in applicant's
United States Patent 7,213,641 which issued May 8, 2007.
Abrasion resistant frac heads significantly reduce frac
head maintenance, but do not eliminate it. Because hardened
steels are brittle, they cannot be used to line a bottom
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end of a central passage through the frac head, which is
subject to impact and compression forces. Consequently,
even abrasion-resistant frac heads require maintenance in
addition to the replacement of the hardened steel inserts.
To facilitate such maintenance, multipart frac heads with
replaceable components were invented, as described in
Assignee's co-pending patent application US11/787,575 filed
April 17, 2007, the entire specification of which is
incorporated herein by reference.
[0004] FIG. 1 is a schematic cross-sectional diagram of one
embodiment of Assignee's multipart frac head 100 described
in the above-identified co-pending patent application. The
multipart frac head 100 has a frac head body 102 and a
plurality of entry ports, two of which (104a, 104b) are
shown. Frac heads are generally equipped with 2-5 entry
ports. In this embodiment side entry ports 104a, 104b are
welded to the frac head body 102 using methods known in the
art. Each side entry port 104a, 104b includes a respective
central bore 106a, 106b in fluid communication with a
mixing chamber 108 of the frac head body 102. A top end of
each side entry port 104a, 104b supports a frac iron
adapter 112a, 112b that is also known in the art.
[0005] The frac head body 102 has a top end 118 with a
central passage 120 in fluid communication with the mixing
chamber 108. In this embodiment, the top end 118 terminates
in a threaded union described in Applicant's United States
Patent 7,125,055 entitled Metal Ring Gasket for a Threaded
Union, which issued on October 24, 2006, the specification
of which is incorporated herein by reference in its
entirety. The threaded union connector is compatible with
a complementary threaded union connector 128 of equipment
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connected to the multipart frac head 100. The equipment is
typically a high-pressure valve, but may be any other well
completion, re-completion or workover equipment.
[0006]A bottom of the mixing chamber 108 has a funnel-shaped
section that tapers inwardly to a central passage 132 of a
bottom leg 134 secured to the frac head body 102. The
tapered bottom end of the mixing chamber 108 is lined with
a wear-resistant insert 146. A lock nut 150 secures the
bottom leg 134 in the frac head body 102. A bottom end of
the bottom leg 134 terminates in a threaded union connector
described in Applicant's above-referenced United States
Patent 7,125,055.
[0007]Although Assignee's multipart frac heads with
replaceable components has significantly reduced
maintenance costs, further improvements are desirable.
[0008]There therefore exists a need for a frac head that is
more quickly and easily constructed and is yet more erosion
resistant than known prior art frac heads.
SUMMARY OF THE INVENTION
[0009] It is therefore an object of the invention to provide
a frac head that is more quickly and easily constructed and
is yet more erosion resistant than known prior art frac
head.
[0010]The invention therefore provides an erosion resistant
frac head, comprising: a frac head body having a top end
with an axial port and a central passage that extends
though the axial port and the frac head body, an annular
shoulder that surrounds the axial port and is downwardly
inclined with respect to the axial port; and at least two
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top entry ports secured in respective circular sockets
machined in the annular shoulder, the circular sockets
communicating with circular bores that communicate with the
central passage.
[0011] The invention further provides an erosion resistant
frac head, comprising: a frac head body having a top end
with an axial port and a central passage that extends
though the axial port and the frac head body, an annular
shoulder that surrounds the axial port and is downwardly
inclined with respect to the axial port; at least two top
entry ports secured in respective circular sockets machined
in the annular shoulder, the at least two top entry ports
being in fluid communication with the central passage; and
the central passage including a convergence chamber where
the axial port and the at least two top entry ports meet,
an expansion chamber with a downwardly and outwardly
inclined sidewall below the convergence chamber and a
mixing chamber below the expansion chamber.
[0012] The invention yet further provides an erosion
resistant frac head, comprising: a frac head body having a
top end with an axial port and a central passage that
extends though the axial port and the frac head body, an
annular shoulder that surrounds the axial port and is
downwardly inclined with respect to the axial port; at
least two top entry ports secured in respective circular
sockets machined in the annular shoulder, the circular
sockets communicating with circular bores that communicate
with the central passage; a bottom leg removably received
in a bottom leg socket in the frac head body, the bottom
leg comprising an inner end received in a seal bore in the
bottom leg socket, the inner end cooperating with high-
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pressure seals in the seal bore to provide a high-pressure
fluid seal around the bottom leg, and an elongated pin
thread that cooperates with the box thread to secure the
bottom leg in the bottom leg socket; a lock nut threadedly
secured to an outer end of the elongated pin thread, the
lock nut being tightened against a bottom end of the frac
head body to lock the bottom leg in the bottom leg socket;
and the central passage including a convergence chamber
where the axial port and the at least two top entry ports
meet, an expansion chamber with a downwardly and outwardly
inclined sidewall below the convergence chamber and a
mixing chamber below the expansion chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013]Having thus generally described the nature of the
invention, reference will now be made to the accompanying
drawings, in which:
[0014] FIG. 1 is a schematic cross-sectional diagram of one
embodiment of Assignee's multipart frac head with
replaceable components;
[0015] FIG. 2 is a schematic cross-sectional diagram of one
embodiment of an erosion resistant frac head in accordance
with the invention;
[0016] FIG. 3 is a schematic cross-sectional diagram of yet
another embodiment of the erosion resistant frac head in
accordance with the invention;
[0017] FIG. 4 is a schematic cross-sectional diagram of a
further embodiment of the erosion resistant frac head in
accordance with the invention;
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[0018] FIG. 5 is a schematic cross-sectional diagram of yet
another embodiment of the erosion resistant frac head in
accordance with the invention;
[0019] FIG. 5a is a schematic plan view of a flange used to
secure top entry ports of the erosion resistant frac head
shown in FIG. 5; and
[0020] FIG. 6 is a schematic cross-sectional diagram of yet
another embodiment of the erosion resistant frac head in
accordance with the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] The invention provides an erosion resistant frac head
that is more quickly and easily constructed, so that costs
associated with frac head construction and assembly are
reduced. The erosion resistant frac head also channels
abrasive fluids into a mixing chamber of the frac head in a
way that reduces turbulence. The reduction of turbulence
reduces erosion due to abrasion, so a service life of the
frac head components is prolonged. In one embodiment the
erosion resistant frac head has a replaceable bottom leg.
The replaceable bottom leg permits the erosion resistant
frac head to be refurbished in the field before it must be
returned to a machine shop to be completely overhauled or
recycled. In another embodiment the top entry ports of the
erosion resistant frac head are also replaceable. This
permits those components to be replaced with new or
refurbished parts using only wrenches. No welding is
required.
[0022] FIG. 2 is a schematic cross-sectional view of one
embodiment of an erosion resistant frac 200 head in
accordance with the invention. Parts for the erosion
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resistant frac head 200 are machined using a CNC (Computer
Numeric Control) boring milling machine, which is known in
the art. The erosion resistant frac head 200 includes a
frac head body 202 with a top end 208 that includes an
annular shoulder 210 that surrounds an axial port 212. The
annular shoulder 210 is downwardly inclined with respect to
the axial port 212. In this embodiment the annular shoulder
210 is downwardly inclined with respect to the axial port
212 at an angle of about 45 with respect to a central axis
of the frac head body 202. A central passage 204 extends
through the axial port 212 and the frac head body 202. The
axial port 212 terminates in a threaded union 214 described
in Assignee's above-referenced United States Patent
7,125,055.
[0023]At least two top entry ports 216a, 216b are secured in
circular sockets 218a, 218b machined in the annular
shoulder 210. Circular bores 220a, 220b having a diameter
equal to an internal diameter of the respective top entry
ports 216a, 216b provide fluid communication between the
respective top entry ports 216a, 216b and the central
passage 204. After the top entry ports 216a, 216b are
inserted into the respective circular sockets 218a, 218b
they are welded in place using a linear weld bead laid
around a periphery of the circular sockets 218a, 218b. This
welding operation is quickly and easily performed after the
parts are preheated, as described in Assignee's above-
referenced co-pending patent application.
[0024] The central passage 204 enlarges downwardly from a
top 219 of the circular bores 220a, 220b to provide a
convergence chamber 221. The convergence chamber 221 is
about 25% wider at a bottom 223 of the circular bores 220a,
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220b than at the top 219. An expansion chamber 222 below
the convergence chamber 221 has a downwardly and outwardly
inclined sidewall 225 that permits converging frac fluid
streams to rapidly expand as they exit the convergence
chamber 221. In this embodiment, the sidewall 225 of the
expansion chamber 222 is downwardly and outwardly inclined
at an angle of about 45 with respect to the central axis
of the frac head body 202. It should be understood that an
angle of inclination of less than or considerably greater
than 45 could be used for the sidewall 225 of the
expansion chamber 222. The shape of the expansion chamber
222 permits the converging frac fluid streams to flow into
the mixing chamber 206 with reduced turbulence. The mixing
chamber 206 is lined with an abrasion resistant liner 224.
The abrasion resistant liner has a cylindrical outer
sidewall 227 and an inner sidewall that has a cylindrical
upper section 229, a downwardly and inwardly inclined
central section 231 and a cylindrical lower section 233. In
this embodiment the abrasion resistant liner 224 is made of
hardened 4140 steel, though any durable abrasion resistant
material including a ceramic material may be used to line
the mixing chamber 206.
[0025]The abrasion resistant liner 224 is supported by a
bottom leg 226 threadedly secured in a bottom leg socket
228 machined into a bottom end 230 of the frac head body
202. The bottom leg socket 228 includes a seal bore 232
located inwardly of a box thread 234. The seal bore
includes two 0-ring grooves 236a, 236b that respectively
accept 0-rings 238a, 238b. A top end 240 of the bottom leg
226 is received in the seal bore 232 and cooperates with
the 0-rings 236a, 236b to provide a high-pressure fluid
seal between the bottom leg 226 and the bottom leg socket
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228. An elongated pin thread 242 on the bottom leg 226
engages the box thread 234 to secure the bottom leg 226 in
the bottom leg socket 228. A lock nut 244 engages an outer
end of the pin thread 234 and is tightened against the
bottom end 230 of the frac head body 202 to inhibit
rotation of the bottom leg 226 with respect to the frac
head body 202. The bottom leg 226 terminates in a threaded
union connector of the type described in Assignee's above-
referenced United States Patent 7,125,055. The threaded
union connector includes a pin end 246 with two 0-rings
248a, 248b received in 0-ring grooves 250a, 250b. A wing
nut 252 is supported by an annular shoulder 254 on a lower
periphery of the bottom leg 226.
[0026]As will be understood by those skilled in the art, the
abrasion resistant liner 224 and/or the bottom leg 226 can
be replaced by field hands using new or refurbished
replacement parts. Consequently, the erosion resistant
frac head 200 is less expensive to maintain. The erosion
resistant frac head 200 is also less expensive to build
because its constructed using machined parts that require
only linear welding to secure the top entry ports 216a,
216b in the circular sockets 218a, 218b. Furthermore,
field tests have established that the erosion resistant
frac head 200 is quite resistant to "wash". Even when
unbalanced input streams of frac fluid are pumped through
the frac head 200, very little wash occurs. This is
unexpected because input streams that are unbalanced in
pressure, volume and/or velocity are known to cause wash in
frac heads.
[0027] FIG. 3 is a schematic cross-sectional view of an
erosion resistant frac head 300 in accordance with the
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invention. The erosion resistant frac head 300 closely
resembles the erosion resistant frac head 200 described
above with reference to FIG. 2. The erosion resistant frac
head body 302 has a longer axial port 312, which provides
better access to threaded union 314. Top end 308 with
annular shoulder 310 supports at least two top entry ports
316a and 316b. The top entry ports are the same as those
described above with reference to FIG. 2. A mixing chamber
306 is lined by an abrasion resistant liner 324 similar to
the one described above with reference to FIG. 2, except
that pancake gaskets 360 and 362 respectively inhibit frac
fluid and propant from migrating from the mixing chamber
306 around the abrasion resistant liner 324. A convergence
chamber 321 and expansion chamber 322 are identical to
those described above, as are other components of the frac
head 300, which will not be redundantly described. it
should be noted that the pancake gaskets 360, 362 could
also be used to seal around the abrasion resistant liner
224 shown in FIG. 2.
[0028] FIG. 4 is a cross-sectional schematic diagram an
erosion resistant frac head 400 in accordance with the
invention. Erosion resistant frac head 400 is similar to
the erosion resistant frac head 300 described above, except
that top entry ports 416a, 416b are threadedly secured in
box threaded circular sockets 418a and 418b machined in an
annular shoulder 410 at a top end 408 of a frac head body
402.
[0029]A pin thread 470a, 470b on an external periphery of an
inner end of the respective top entry ports 416a, 416b
engages a box thread 472a, 472b in the respective box
threaded circular sockets 418a and 418b. A cylindrical
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terminal end 474a, 474b of the respective top entry ports
416a, 416b is received in respective seal bores 476a, 476b
at a bottom of the respective circular sockets 418a, 418b.
High pressure 0-rings 478a,b and 480a,b respectively
received in 0-ring grooves 482a,b and 484a,b in the
respective circular sockets 418a, 418b provide a high-
pressure seal around each top entry port 416a, 416b.
Although the 0-rings 478a,b and 480a,b are shown in the 0-
ring grooves 482a,b and 484a,b in the respective seal bores
476a, 476b, it should understood that the seal bores 476a,
476b could be smooth bores and the 0-rings could be
received in 0-ring grooves on the terminal ends 474a, 474b
of the top entry ports 416a, 416b.
[0030] Lock nuts 488a, 488b inhibit rotation of the
respective top entry ports 416a, 416b. The lock nuts 488a
and 488b respectively include an annular boss 490a, 490b on
their bottom surface. The annular boss 490a, 490b has an
outer edge that is downwardly and inwardly inclined. In
this embodiment the outer edge of the annular boss 490a,
490b is inclined at an angle of about 45 , although any
angle from 30 to 90 can be used. The annular boss 490a,
490b is received in a respective complementary socket 492a,
492b when the respective lock nuts 488a, 488b are tightened
against the annular shoulder 410. The annular boss 490a,
490b reinforces the respective top entry ports 416a, 416b
against vibration and other applied forces when frac irons
(not shown) are connected to the top entry ports 416a, 416b
and frac fluid is pumped through the frac head 400.
[0031]FIG. 5 is a cross-sectional schematic diagram of yet
another embodiment of the erosion resistant frac head in
accordance with the invention. Erosion resistant frac head
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500 is identical to the erosion resistant frac head 400
described above, except that top entry ports 516a, 516b are
reinforced against vibration and other applied forces by
circular flanges 520a, 520b (see also FIG. 5a). The
circular flanges 520a, 520b are connected to the annular
shoulder 510 by a plurality of bolts 522 that are received
in threaded bores 523 in the annular shoulder 510. A cut
away inner bottom corner 524a, 524b of the flanges 520a,
520b receives an outer side of circular segments 526a,
526b. The circular segments 526a, 526b are respectively
received in annular grooves 528a, 528b in an outer sidewall
of the respective top entry ports 516a, 516b.
[0032]The top entry ports 516a, 516b are installed in the
frac head 500 by placing the respective flanges 520a, 520b
over respective bottom ends of the top entry ports 516a,
516b before they are screwed into their respective box
threaded circular sockets. Before the respective top entry
ports 516a and 516b are tightened down in their box
threaded circular sockets, the circular segments 526a, 526b
are inserted into the respective annular grooves 528a and
528b. The respective top entry ports 516a, 516b are then
tightened down and the respective flanges 520a and 520b are
aligned with the threaded bores 523. The bolts 522 are then
treaded into the threaded bores 523 to fasten the
respective flanges 520a, 520b securely in place. As
explained above, the circular segments 526a, 526b and the
secured flanges 520a, 520b reinforce the respective top
entry ports 516a, 516b against vibration and other applied
forces when frac irons (not shown) are connected to the top
entry ports 516a, 516b and frac fluid is pumped through the
frac head 500. It should be understood that the circular
segments 526a,b described above could be replaced by an
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integral annular shoulder on an outer periphery of the
respective top entry ports 516a, 516b.
[0033] FIG. 6 is a schematic cross-sectional view of frac
head 600 in accordance with the invention, which
illustrates an alternate method of sealing a space between
the frac head body 602 and the abrasion resistant liner
624. In this embodiment, an 0-ring groove 692 in the frac
head body 602 near a top end of the abrasion resistant
liner 624 accepts a high-pressure 0-ring 694 that
cooperates with an outer wall of the abrasion resistant
liner 624 to inhibit a migration of frac fluids into a
space between the abrasion resistant liner 624 and the frac
head body 602. Likewise, an 0-ring groove 696 in the frac
head body 602 near a bottom end of the abrasion resistant
liner 624 accepts a high-pressure 0-ring 698 that
cooperates with an outer wall of the abrasion resistant
liner 624 to inhibit a migration of frac fluids into a
space between the abrasion resistant liner 624 and the frac
head body 602.
[0034] It should be understood that the 0-rings 694, 698
received in the 0-ring grooves 692, 696 shown in FIG. 6
could also be used to seal the space between the abrasion
resistant liner and the frac head body of any one of the
embodiments of the invention described above with reference
to FIGs. 2-5. When the 0-rings 694, 698 are used, the
pancake gaskets described above are unnecessary, and when
the pancake gaskets are used the 0-rings are unnecessary.
[0035] While various embodiments of the frac heads in
accordance with the invention have been described, it
should be understood that the embodiments described above
are exemplary only. For example, the frac heads 200, 300,
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400, 500 or 600 may be constructed with an integral bottom
leg as taught in Assignee's United States Patent 7,213,641
which issued on May 8, 2007, the specification of which is
incorporated herein by reference in its entirety. Other
changes within the skill of an ordinary person in the art
may also become apparent.
[0036]The scope of the invention is therefore intended to be
limited solely by the scope of the appended claims.
