Note: Descriptions are shown in the official language in which they were submitted.
CA 02276973 1999-07-07
TUBING HEAD SPOOL
TECHNICAL FIELD
The present invention relates to equipment for
servicing oil and gas wells and, in particular, to a
tubing head spool which is adapted to be used in a high
pressure stimulation treatment of an oil or gas well
using a blowout preventer protector.
BACKGROUND OF THE INVENTION
The servicing of oil or gas wells to stimulate
production requires the pumping of fluids under high
pressure. The fluids are generally corrosive and/or
abrasive because they are frequently laden with corrosive
acids and/or abrasive proppants such as sharp sand. Some
hydrocarbon producing formations require stimulation and
extreme pressures to break up the formation and improve
the flow of hydrocarbons to the well. If such wells are
equipped with a wellhead, it is advantageous to use
specialized tools called wellhead isolation tools which
are inserted through the wellhead and related equipment
to isolate pressure sensitive components from the extreme
pressure required to stimulate those wells. Wellhead
isolation tools are taught, for example, in United States
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Patent Nos. 4,867,243, 5,332,044 and 5,372,202 which
issued to the Applicant respectively on
September 19, 1989, July 26, 1994 and December 13, 1994.
In other wells, stimulation to improve
production can be accomplished at more moderate pressure
which may be safely contained by blowout preventers
(BOPS) attached to the well casing. In those instances,
some operators remove the wellhead equipment and pump
stimulation fluids directly through a valve attached to
the BOPS. This procedure is adopted to minimize expense
and to permit full access to the well casing with tools
such as logging tools, perforation guns and the like
during the well servicing operation.
When pumping abrasive fluids into a well, the
pump rate must be kept high to place the proppants
without "screening out", in which a blockage occurs
and/or the equipment including the high pressure lines
are blocked with abrasive injected under high pressure.
When the pump rate is high or large quantities of
proppants are pumped, the BOPS may be damaged by the
cutting action of the proppant. If high rates of
abrasive proppants are pumped through a BOP, the blind
ram of the BOP or the valve gates can be "washed out" so
that the BOP becomes inoperable.
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If stimulation treatments are to exceed
pressures at which the wellhead equipment is rated, a
wellhead isolation tool, a casing saver or a casing
packer have to date been the only tools available for
isolating the wellhead from extreme pressure and
abrasion. Although it is not uncommon for certain wells
to be stimulated at pressures which do not exceed the
pressure rating of the wellhead equipment (about
5000 psi), it is quite common that wells require extreme
pressure treatments (usually in the range of 10,000 to
15,000 psi) for production stimulation. If the
stimulation pressure is higher than 5,000 psi, the BOPS
must be protected from the pressure because they are not
constructed to contain extreme pressures.
A protector for protecting a blowout preventer
from exposure to fluid pressure as well as abrasive
and/or corrosive fluids during well fracturing and/or
stimulation treatment to stimulate production comprises a
spool which is mounted above the blowout preventer. A
mandrel can be stroked down from the spool through the
blowout preventer until an annular seal engages a top end
of the casing to isolate the blowout preventer and
protect it from exposure to fluid pressure as well as
abrasive and/or corrosive fluids during well stimulation
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treatments, and strok.ec_~ uut:. rf t.i~e blowout preventer
after the well has been stvm~.r~.at~e~:i. TY:e BOP protector is
described in United States Patent No. 5,819,851, which
issued on October L3, 19~~8.
Although ttncBC>P prot:ec~t:or de~;cr_:ibed above
represents a si.grui f ic.:~arxt: advanc:r iru t.ha:~ arty, its use is
limited to the pressure rating o2v t::.he tubing head spocl
in which it is packeci off. This i~. due to the annular
seal which is radia_Lly ~uppor ted by the tubing head
spool. The annular sea'~_ between i:.hce mandrel and a
secondary seal in the t,~ubi_nc~ hie~.~~d sp~::~01 is an elastic
seal which contains tine high pressire ~Yorrosive fluids
but it is not adapted to ~;orrtain t~.e rvadial pressure to
which it is exposed. The annular seal therefore exerts
the same radial pressure agairm~ t t~tie r~upporting surface
of the inner periphet_y of tlue~ t.ub:irig huf~ad spool as the
fluid pressure it cant ai.n:>. f.onsequent:Ly, well
stimulation treatments cannot be safely conducted at
pressures above the pressure rating of the tubing head
spool, typically 5,000 psi.. Tubinq head spools having
higher pressure ratings are cc~rnrne r~~ is :l.l y available but
they are expensive ~~nd ace :upe~rf~uo~..m~ unless a well
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requires high pressure stimulation. It is therefore
desirable to provide a tubing head spool which may be
made commercially available at a reasonable price but
adapted to be used in a stimulation process using higher
pressure fluids.
SUI~lARY OF THE INVENTION
An object of the invention is to provide a
tubing spool which is inexpensive to manufacture but may
be used with a BOP protector to effect high pressure well
stimulation treatments.
Another object of the invention is to provide
an improved tubing head spool generally having a low
pressure rating which is adapted to be used with a BOP
protector for high pressure fracturing and stimulation
treatments.
It is yet a further object of the invention to
provide a method of stimulating a well to improve
production using a BOP protector and a tubing head spool
having a low general pressure rating but adapted to be
used with the BOP protector for high pressure stimulation
treatments.
In accordance with one aspect of the invention,
there is provided a tubing head spool which comprises a
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top flange adapted for mounting wellhead components
thereto, a bottom flange adapted to mount to a surface
flange of a hydrocarbon well and to connect with a casing
of the well and a sidewall that extends between the top
and bottom flanges to define a profile adapted for
accepting a tubing hanger; the top flange, the bottom
flange and a substantial portion of the sidewall having a
first pressure rating and a reinforced area of the
sidewall adjacent the bottom flange having a second
pressure rating that is greater than the first pressure
rating, the reinforced area of the sidewall being adapted
to surround and support a seal of a blowout preventer
(BOP) protector when the BOP protector is packed off
against a top of the casing.
The reinforced area of the sidewall extends
above a portion of the profile that receives the
secondary seal. The secondary seal preferably includes a
bit guide at a top thereof and the reinforced area of the
sidewall extends above a portion of the profile at a top
of the bit guide.
The tubing head spool is isolated from exposure
to high pressure corrosive fluids when the mandrel of the
BOP protector is stroked down through the tubing head
spool and the annular seal sealingly engages the
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secondary seal. Therefore, the pressurized fluids used
for well stimulation treatments are contained in the
mandrel by the secondary seal. Nonetheless, the annular
seal of the BOP protector is elastic. Since it is
supported by the sidewall of the tubing head, it exerts
radial pressure thereon which is equal to a fluid
pressure of the well stimulation fluids. The reinforced
area of the sidewall is thicker than the rest of the
sidewall, however, and has a higher pressure rating so
that the tubing head spool may be used to effect high
pressure stimulation treatments up to the second pressure
rating when a BOP protector is sealed against the
secondary seal.
In accordance with another aspect of the
invention, there is provided a method of using a tubing
head spool with a mandrel in fracturing or stimulating a
hydrocarbon well, the tubing head spool having a top
flange adapted for mounting wellhead components thereto,
a bottom flange which is mounted to a surface flange of
the well and connected to a casing of the well by a
secondary seal, and a sidewall extending between the top
and bottom flanges, the tubing head spool having a first
pressure rating except for a reinforced area of the
sidewall adjacent the bottom flange, the reinforced area
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surrounding and extending above the secondary seal and
having a second pressure rating that is greater than the
first pressure rating, the method comprising inserting
the mandrel into the tubing head spool from a top
thereof, the mandrel being connected to a high pressure
fluid supply for fracturing or stimulating the
hydrocarbon well, a bottom end of the mandrel including
an annular seal means for high pressure sealing
engagement with a top of the secondary seal; sealing the
annular seal means against the secondary seal so that the
annular seal means is surrounded and supported by the
reinforced area of the sidewall having the second
pressure rating; fracturing or stimulating the well by
controllably introducing high pressure fluids from the
supply source though the mandrel and into the casing; and
removing the mandrel from the tubing head spool after the
fracturing or stimulation process is complete and the
fluid pressure has been bled off.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be explained in more
detail by way of example only and with reference to the
following drawings, wherein:
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FIG. 1 is a cross-sectional view of a prior art
tubing head spool connected with a blowout preventer and
a BOP protector in service for well stimulation
treatment;
FIG. 2 is a side view of a prior art tubing
head spool partially in cross-section to show the inside
thereof when it is in service as illustrated in FIG. 1;
FIG. 3 is a cross-sectional view of a secondary
seal used with the tubing head spool illustrated in
FIG. 2;
FIG. 4 is a side view of one preferred
embodiment of the invention partially in cross-section to
show the inside thereof; and
FIG. 5 is a cross-sectional view of the
embodiment illustrated in FIG. 4 to show the inside
thereof when it is in service in the same way as
illustrated in FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows a prior art tubing head spool
connected with a BOP protector in service for a well
stimulation treatment. The BOP protector 10 is mounted
above a BOP 40 and a high pressure valve spool 60 is
mounted to the top of the BOP protector 10. An adapter
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spool 70 may be mounted above the high pressure valve
spool 60. The BOP 40 is connected through a tubing head
spool 100 to a top end of a casing spool 80 in a manner
well known in the art. The BOP protector 10 comprises a
protector spool 12 having a top end 14, a bottom end 16,
and spaced apart inner and outer sidewalls 18 and 20 that
extend between the top end 14 and the bottom end 16. The
bottom end 16 is mounted above the BOP 40 and the top end
14 is adapted for the attachment of another spool or a
union, or a high pressure valve spool 60. The BOP
protector 10 is provided with a mandrel 22 which has a
top end 24 and a bottom end 26, the top end 24 being
received in an annular cavity between the inner and outer
sidewalls 18 and 20 and forcibly reciprocatible within
the cavity by pressurized fluids which can be introduced
or drained from either top port 25 or bottom port 27.
The bottom end 26 of the mandrel 22 includes a mandrel
extension 28 and a mandrel pack-off assembly 30 which
supports an annular seal 32 for high pressure sealing
engagement with a secondary seal 102 at the bottom of the
tubing head spool 100.
FIG. 2 is a detailed view of the tubing head
spool 100 illustrated in FIG. 1. The tubing head spool
100 comprises a top flange 120 adapted for mounting
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wellhead components thereto, such as a blowout preventer
40 as shown in FIG. 1; a bottorr~ flange 122 adapted to be
mounted to a surface flange c>f a ~cas__ng spool 80 of a
hydrocarbon well and to cc>rmect wit.tv a casing 82 of the
well; a sidewall 124 that. E::~tends between the top and
bottom flanges 122 tc: define a ct~~ntral passage126
120,
adapted for accepting Two
a t~~biraq
hancy:ar
(Trot shown)
.
studded side outlets l<?8 extend t.ran:~vEarsely t=hroughthe
si.dewal7_ , respectively and a ~sl.uxal.:~ty of studs are
130
provide<_~around each s:ic~e outlets 1<=8 c;n a plain face
sur
131 for eonnec:tion of a f? anc~ed c~ut:let thereto (not
shown) . The t~ubi head spc~c:l. ~ ~~ p r~;>vided lock
ng with
screw as semblies 132 <~t the top flange 120 in suffic ient
quantity to support the tubing hange:r.. Each of the lock
screw assemblies 132_ inc:lude:, manually energized
elastomer seals for safe and effective pressure
isolation, which is well known in the art. The central
passage 126 includes a tubing hanger segment 127, a
middle segment 12~ wi.th whic::h the t.we side outlets 128
communicate, and a lover segnuerut: :L29. The lower segment
129 receives a secorudarvy seal 1U2 to isolate annulus
pressure. This secondary ~ea1 102 wot~!: rol_s arid isolates
pressure. Secondary seals are knc:awro t. c: be efficient and
reliable in various appl i.ca ti.ons . 'l:'he bottom f=lange 122
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contains a pressure test port 134, which permits positive
testing of annular seals.
FIG. 3 shows a commonly used secondary seal
preferably used in a tubing head spool in accordance with
the invention. The secondary seal provides an integral
bit guide 136. Bit guide 136 protects the seal bore and
helps direct inner tubular strings. Inside diameters of
the bit guide 136 maintain a minimum restricted bore
based on the lightest standard casing weight. The
secondary seal 106 comprises an interchangeable sleeve
139 and incorporates a mechanically energized elastomer
ring 142 to maintain annular pressure isolation. The
sleeve 139 in the secondary seal has channels 146 that
communicate with a sealant port 144 in the bottom flange
122 of a tubing head spool and the annular groove in
which the elastomer ring 142 is received. This type of
seal provides' dependable service up to 10,000 psi.
A preferred embodiment of the invention is
illustrated in FIG. 4. The tubing head spool 200 of the
preferred embodiment is similar in structure to the
tubing head spool 100 shown in FIG. 2. The tubing head
spool 200 comprises a top flange 120 adapted for mounting
wellhead components thereto; a bottom flange 122 adapted
to mount to the surface flange of the casing spool 80 and
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to connect with the casing 82 of the well; and a sidewall
224 that extends between the top and bottom flanges 120,
122 to define a central passage 226 for accepting a
tubing hanger. The sidewall 224 preferably includes two
side outlets 128 transversely extending through the
sidewall 224 respectively. A plurality of studs 130 are
provided around each of the side outlets 128 on a plain
surface 131 for connection of flanged outlets (not
shown). The bottom flange 122 contains a test port 134
for positive testing of annular seals and a sealant port
144 which communicates with the channels of secondary
seal 106 shown in FIG. 3 for injection of plastic
packing.
The central passage 226 includes a tubing
hanger segment 125 which has a diameter slighter greater
than a diameter of a middle segment 227. The side
outlets 128 communicate with the middle segment 227. A
lower segment 129 of the central passage 226 has a
diameter greater than the diameter of the middle segment
227 to receive the secondary seal 106. Lock screw
assemblies 132 are also provided in the top flange 120 in
sufficient quantity to lock down a tubing hanger in the
tubing hanger segment 125. The tubing head spool 200
includes a reinforced area R of the sidewall which
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extends upwardly from the bottom flange 122 about 4 to 5
inches (10 to 13 cm) from a top of the secondary seal
106. The reinforced area R has a pressure rating greater
than the pressure rating of the remainder of the tubing
head spool 200. In this embodiment, the reinforced area
R of the sidewall 224 has a pressure rating of 10,000 psi
and the remainder of the tubing head spool 200 has a
pressure rating of 5,000 psi. Therefore, a fluid
pressure of up to 10,000 psi that is transferred by a
thermoplastic or synthetic rubber annular seal 32 of a
BOP protector during a well stimulation treatment to the
sidewall 224 is safely contained by the reinforced area R
of the sidewall 224. It will be understood that the
pressure rating of the reinforced area R is a matter of
design choice and it may be more or less than 10,000 psi,
as required.
A method of using the tubing head spool 200
with a BOP protector 10 in fracturing or stimulating a
hydrocarbon well will now be described. The tubing head
spool 200 and a blowout preventer 40 are normally
installed as a part of the original wellhead equipment.
To begin the fracturing or stimulating treatment, the
blowout preventer 40 is closed and any wellhead equipment
above it is removed. The BOP protector 10 is mounted to
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the blowout preventer 40 and ~~ high pressure valve is
mounted above the BGP protector and is tightly closed.
The blowout preventer 40 is fu.l.ly opened and the mandrel
22 with the mandrel extension 28 of thca BOP protector 10
is fully extended th:rc~ucTh t:he b7.ow<out preventer 40 and
:inserted into t:he t.~bing r~.eader :~po;:,>1 200 unti:L the
annular seal 32 is seale.~ a:~bove true .;ec.oradary sea:1 1.06 so
that the annular seal 32 i s surr~ur~dE:c.i and supported by
the reinforced area R of the sidewall which has the
higher pressure rating of 10,000 psi, for example. A
high pressure fluid ~~uppl~,~ is c~onne.rt;:vd through a high
pressure' line (not snc:>wo) and 'tzigti. pressure fluids are
controllably intrc:due,.ed f'rorn t.tie supply through. the
mandrel 22 and rnandre:L extc~n:.>i.or; 20 ,u:E the BOP protector
=0 to the casing "2 tc> perfc.~rrn the-, fracturing or
stimulation treatment at fluid pressure:; up to the righer
pressure rating. After fracturing or stimulation
treatment is complete, the mandrel 2t' a.nd the mandrel
extension 28 are removed from thle tubinc::~ header spool 200
and further ret~rac-teca of the ~:>:l.ow;:~utprevente:r
o:zt 40.
The blowout preventer 40 c_.lo~:,ec~ and high pressure
i,~ the
line is removed after the-: fluid pressure in the high
pres sure line is bled-of "''he BOP prc~~tector
f . 10 and the
high pressure valve are a lso removed and the wellhead
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equipment is replaced to permit hydrocarbon production to
resume.
Changes and modifications to the embodiments of
the invention described above will no doubt become
apparent to those skilled in the art, the scope of the
invention is therefore intended to be limited solely by
the scope of the appended claims.
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