UNITED STATES PATENT AND TRADEMARK OFFICE
`
`BEFORE THE PATENT TRIAL AND APPEAL BOARD
`
`
`
`GREENE’S ENERGY GROUP, LLC,
`
`Petitioner,
`
`v.
`
`OIL STATES ENERGY SERVICES, LLC,
`
`Patent Owner.
`
`
`
`Case IPR2014-00216
`
`Patent No. 6,179,053
`
`PATENT OWNER PRELIMINARY RESPONSE
`UNDER 37 C.F.R. § 42.107
`
`
`
`EXHIBIT A
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`United States Patent [19J
`Dallas
`
`111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US005819851A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,819,851
`Oct. 13, 1998
`
`[54] BLOWOUT PREVENTER PROTECTOR FOR
`USE DURING HIGH PRESSURE OIL/GAS
`WELL STIMULATION
`
`[76]
`
`Inventor: L. Murray Dallas, 801 New England
`Ct., Allen, Tex. 75002
`
`[21]
`
`Appl. No.: 783,860
`
`[22]
`
`Filed:
`
`Jan. 16, 1997
`
`[51]
`[52]
`
`[58]
`
`[56]
`
`Int. Cl.6
`................................................... E21B 33/068
`U.S. Cl. ........................ 166/308; 166/86.1; 166/87.1;
`166/90.1; 166/386; 166/387
`Field of Search ..................................... 166/308, 386,
`166/387, 86.1, 87.1, 90.1
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,076,079
`4,832,128
`4,993,488
`5,012,865
`5,332,044
`5,372,202
`
`2/1978 Herricks et a!. .................... 166/387 X
`5/1989 Light et a!. .
`2/1991 McLeod .
`5/1991 McLeod .
`7/1994 Dallas eta!. ............................ 166/386
`12/1994 Dallas ..................................... 166/386
`
`Primary Examiner-Roger 1. Schoeppel
`Attorney, Agent, or Firm---Dority & Manning, P.A.
`
`[57]
`
`ABSTRACT
`
`An apparatus for protecting blowout preventers during well
`fracturing and/or stimulation treatments is disclosed. The
`apparatus includes a hollow spool with spaced-apart inner
`and outer sidewalls that define an annular cavity. A mandrel
`is forcibly reciprocatable in the cavity. The mandrel includes
`an annular seal at a bottom end for sealingly engaging a bit
`guide attached to a top end of the casing. The apparatus is
`mounted above a BOP attached to a casing spool of the well
`before well stimulation procedures are begun. The mandrel
`is stroked down through the BOP to protect it from exposure
`to fluid pressure as well as abrasive and/or corrosive well
`stimulation fluids, especially extreme pressures and abrasive
`proppants. The advantage is a simple, easy to operate
`apparatus for protecting BOPs which provides full access to
`the well casing with well servicing tools to facilitate well
`stimulation at pressures approaching the burst pressure
`rating of the well casing.
`
`45 Claims, 5 Drawing Sheets
`
`28
`
`42
`
`

`

`U.S. Patent
`US. Patent
`
`Oct. 13, 1998
`Oct. 13, 1998
`
`Sheet 1 of 5
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`U.S. Patent
`US. Patent
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`Oct. 13, 1998
`91
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`Sheet 2 of 5
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`Oct. 13, 1998
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`U.S. Patent
`US. Patent
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`Oct. 13, 1998
`Oct. 13, 1998
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`Sheet 4 of 5
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`U.S. Patent
`US. Patent
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`Oct. 13, 1998
`Oct. 13, 1998
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`Sheet 5 of 5
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`5,819,851
`
`1
`BLOWOUT PREVENTER PROTECTOR FOR
`USE DURING HIGH PRESSURE OIL/GAS
`WELL STIMULATION
`
`TECHNICAL FIELD
`
`The present invention relates to equipment for servicing
`oil and gas wells and, in particular, to apparatus for protect(cid:173)
`ing blowout preventers from high pressures and exposure to
`abrasive and/or corrosive fluids during well fracturing and/
`or stimulation procedures and a method of servicing oil and 10
`gas wells using same. An apparatus for protecting blowout
`preventers is disclosed in U.S. application Ser. No. 08/661,
`995 for Blowout Preventer Protection and Method of Using
`Same During Oil and Gas Well Stimulation, the entire
`disclosure of which is incorporated by referenced herein.
`
`15
`
`2
`single set without changing the wellhead or wellhead iso(cid:173)
`lation equipment. Furthermore, the well casing packer
`taught by McLeod can only be set in a well which is not
`under pressure at the beginning or end of a servicing
`5 operation. It cannot be used in wells with any natural
`pressure, and is therefore very limited in its utility.
`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 also quite common that wells require extreme
`pressure treatments (usually in the range of 10,000-15,000
`psi) for production stimulation. If the stimulation pressures
`are in the moderate range of 5,000 psi or less, well stimu(cid:173)
`lation can be accomplished directly through the BOPs, but
`unless the BOPs are protected from the abrasive and/or
`20 corrosive fluids used in the stimulation processes, there is
`considerable risk that the BOPs will be damaged and may be
`damaged to an extent that the well must be killed and the
`BOPs replaced because they are no longer functional. If the
`stimulation pressures are higher than 5,000 psi the BOPs
`25 must be protected from the pressure as they are not con(cid:173)
`structed to contain extreme pressures. Regardless of the
`stimulation pressures, it has become increasingly evident
`that it is advantageous to have full access to the well casing
`during a well stimulation treatment. Full access to the casing
`30 permits the use of downhole tools which are often required,
`or at least very advantageously used, during a stimulation
`treatment. If a downhole tool is required during a stimulation
`treatment using a tree saver, a casing saver or casing packer,
`it must be pulled before the tool can be inserted into the
`35 casing. This is time consuming and expensive for the well
`owner who must often pay service crews to stand by or to
`take down and set up again, all of which contributes to
`production expense. It is therefore preferable that full access
`to the well casing be provided whenever a stimulation
`40 treatment is performed.
`It is therefore a primary object of the invention to provide
`a protector for a BOP which will protect the BOP from
`damage due to exposure to high pressures, abrasive prop(cid:173)
`pants and/or corrosive stimulation fluids.
`It is a further object of the invention to provide a protector
`for a BOP which protects the BOP from well stimulation
`pressures and fluids without restricting access to the well
`casing so that well servicing tools such as perforating guns,
`plug setters, logging tools or other related equipment can be
`run into and out of the well while the protector for the BOP
`is in place.
`It is yet a further object of the invention to provide a
`protector for a BOP which is simple to manufacture, easy to
`55 use and capable of containing even extreme well stimulation
`pressures.
`It is still a further object of the invention to provide a
`method of stimulating wells using high pressures while
`protecting a BOP mounted to a top of the well from exposure
`to excessive pressures and abrasive and/or corrosive fluids.
`
`BACKGROUND OF THE INVENTION
`
`The servicing of oil and 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 at 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 iso(cid:173)
`lation tools which are inserted through the wellhead and
`related equipment to isolate pressure sensitive components
`from the extreme pressures required to stimulate those wells.
`Wellhead isolation tools are taught, for example, in U.S. Pat.
`Nos. 4,867,243, 5,332,044 and 5,372,202 which issued to
`the applicant respectively on Sep. 19, 1989, Jul. 26, 1994
`and Dec. 13, 1994.
`In other wells, stimulation to improve production can be
`accomplished at more moderate pressures 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 proppant without "screening out," in 45
`which a blockage occurs and all the equipment including the
`high pressure lines are blocked with abrasives injected under
`high pressure. When the pump rate is high or large quantities
`of proppant are pumped, the BOPs may be damaged by the
`cutting action of the proppant. If high rates of abrasive 50
`proppant are pumped through a BOP, the blind rams of the
`BOP or the valve gates can be "washed out" so that the BOP
`becomes inoperable.
`In addition to wellhead isolation tools, casing savers are
`also used to protect wellhead equipment from extreme
`pressures and well stimulation fluids. Casing packers as
`described in U.S. Pat. No. 4,939,488 which issued Feb. 19,
`1991 to McLeod have likewise been used. While casing
`savers and packers are useful in protecting wellhead equip(cid:173)
`ment including BOPs, they have the disadvantage of restrict- 60
`ing access to the casing because they constrict the through
`bore diameter from the high pressure valve to the casing.
`This restricts flow which can limit the pump rate. It also
`interferes with running servicing tools such as perforating
`guns, plug setters, or other such tools into the casing. It is 65
`advantageous to be able to run tools during well servicing
`operations so that multi-zone wells can be serviced in a
`
`SUMMARY OF THE INVENTION
`These and other objects of the invention are realized in an
`apparatus for protecting a blowout preventer from exposure
`to fluid pressure as well as abrasive and/or corrosive fluids
`during a well fracturing and/or stimulation treatment to
`stimulate production, comprising:
`
`

`

`5,819,851
`
`3
`a spool having a spool top end, a spool bottom end, and
`spaced-apart inner and outer sidewalls that extend
`between the spool top end and the spool bottom end;
`the spool bottom end being adapted to be mounted above
`a blowout preventer;
`the spool top end being adapted for the attachment of
`another spool or a valve;
`a mandrel having a mandrel top end and a mandrel bottom
`end, the mandrel top end being received in an annular
`cavity between the inner and outer sidewalls and forc(cid:173)
`ibly reciprocatable within the cavity, and the mandrel
`bottom end including annular sealing means for high
`pressure sealing engagement with a top end of a casing
`of the well;
`whereby, when the spool is mounted above a blowout
`preventer, the mandrel can be stroked down through the
`blowout preventer until the annular sealing means
`sealingly 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 treatments, and stroked up out
`of the blowout preventer after the well has been stimu(cid:173)
`lated.
`In accordance of a further aspect of the invention, there is
`provided a method of fracturing or stimulating a well having
`at least one blowout preventer attached to a casing of the
`well, comprising the steps of:
`a) mounting above the blowout preventer an apparatus for
`protecting the blowout preventer from exposure to fluid
`pressure as well as abrasive and/or corrosive fluids
`during the well fracturing and/or stimulation treatment
`to stimulate production, the apparatus comprising a
`protector spool having a spool top end, a spool bottom
`end, and spaced-apart inner and outer sidewalls that
`extend between the spool top end and the spool bottom
`end, the spool bottom end being adapted to be mounted
`above the blowout preventer; the spool top end being
`adapted for the attachment of another spool or valve,
`and a mandrel having a mandrel top end and a mandrel
`bottom end, the top mandrel end being received in an
`annular cavity between the inner and outer sidewalls
`and forcibly reciprocatable within the cavity, and the
`mandrel bottom end including annular sealing means
`for high pressure sealing engagement with a top end of
`a casing of the well;
`b) mounting at least one high pressure valve above the
`apparatus;
`c) closing the at least one high pressure valve;
`e) fully opening the blowout preventer;
`f) stroking the mandrel of the apparatus through the
`blowout preventer until the annular sealing means is in
`fluid tight sealing engagement with a top of the casing
`of the well;
`g) stimulating or fracturing the well by pumping high
`pressure fluids and/or proppants through the at least one
`high pressure valve and the apparatus into the casing of
`the well using at least one high pressure valve attached
`to the at least one high pressure valve;
`h) stroking the mandrel out of the blowout preventer;
`i) closing the blowout preventer;
`j) bleeding off the fluid pressure in the at least one high
`pressure line;
`k) removing the at least one high pressure line; and
`1) removing the apparatus and the at least one high
`pressure valve.
`
`4
`The apparatus in accordance with the invention comprises
`a spool which may be mounted above a blowout preventer
`that is mounted either directly or indirectly to a surface
`casing spool. The spool includes inner and outer concentric
`5 walls which are spaced apart to form an annular cavity that
`accommodates a mandrel having a mandrel top end that is
`forcibly reciprocatable within the cavity using fluid
`pressure, and a mandrel bottom end which includes a sealing
`means for sealingly engaging a top end of a casing of the
`10 well. In a preferred embodiment of the invention, the sealing
`means is an annular sealing body of plastics or rubber
`material bonded to a packoff bottom end of an extension for
`the mandrel. In the preferred embodiment, the sealing means
`is adapted to abut a bit guide surrounding a top end of the
`15 casing and to seal against it. A top end of the spool in
`accordance with the invention is adapted for the attachment
`of a high pressure valve, a spool header, or a valve spool
`through which well stimulation fluids can be pumped, and an
`adapter spool or a union such as a thread half or a Bowen
`20 union through which wireline, coil tubing or service tools
`can be run.
`The spool in accordance with the invention for protecting
`BOPs can therefore be used in a novel method of servicing
`wells which permits tools such as logging tools, perforating
`25 guns, plugs, plug setting tools, fishing tools and related
`equipment to be used during the well servicing operation,
`thus permitting the servicing of multi-zone wells to proceed
`without interruption. This is an important advantage because
`it obviates the necessity of having service rigs set up and
`30 taken down for each production zone of a multi-zone well.
`The spool in accordance with the invention for protecting
`BOPs can also be used in a high pressure wellhead assembly
`that includes a high pressure valve spool and a high pressure
`adapter spool that has a tubing pin machined into it. This
`35 permits a tubing string to be hung through the complete
`wellhead assembly. The tubing string may be a production
`tubing already in the well or a coil tubing string run in for
`the job. The tubing string can be used as a dead string for
`measuring downhole pressure during the well stimulation
`40 treatment. In that case, well stimulation fluids are pumped
`through the high pressure valve spool which preferably
`includes at least two high pressure ports. If coil tubing is
`used, the top end of the coil tubing is preferably protected
`from abrasion by a length of "blast joint" that surrounds the
`45 tubing to prevent erosion. Alternatively, a Bowen union can
`be fitted to a top of the adapter spool to permit wireline,
`perforating guns, plug setters or other tools to enter the
`wellhead without obstruction. Or, a high pressure valve can
`be mounted to the adapter flange so that high pressure fluids
`50 can be pumped through up to three ports simultaneously to
`permit very high volume injections into the well.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`55
`
`The invention will now be explained in more detail by
`way of example only, and with reference to the following
`drawings, wherein:
`FIG. 1 shows a longitudinal cross-sectional view of a
`blowout preventer protector in accordance with the
`60 invention, showing the mandrel in a partially stroked-out
`position; and
`FIG. 2 shows a cross-sectional view of the blowout
`preventer protector shown in FIG. 1 attached to a blowout
`preventer on a wellhead and in a position for performing
`65 well stimulation procedures;
`FIG. 3 is a cross-sectional view of a blowout preventer
`protector in accordance with another embodiment of the
`
`

`

`5,819,851
`
`5
`invention wherein the blowout preventer protector includes
`an annular seal for isolating the blowout preventer on the
`wellhead from fluid pressure used in well stimulation treat(cid:173)
`ments;
`FIG. 4 is a cross-sectional view of a blowout preventer
`protector and related spools mounted on a wellhead above a
`blowout preventer and stroked through the blowout preven(cid:173)
`ter in a position for a well stimulation treatment.
`FIG. 5 is a cross-sectional view of a blowout preventer
`protector and related spools mounted on a well head above
`a blowout preventer and stroked through the blowout
`preventer, with a coil tubing run into the well to serve as a
`dead string for monitoring downhole pressures during well
`stimulation treatments.
`
`DETAILED DESCRIPTION OF 1HE
`PREFERRED EMBODIMENT
`FIG. 1 shows a cross-sectional view of the apparatus for
`protecting BOPs (hereinafter BOP protector) in accordance
`with the invention, generally indicated by the reference 10.
`The apparatus includes a hollow spool12 having a spool top
`end 14 and a spool bottom end 16 with an inner sidewall18
`and an outer sidewall 20 arranged in a space-apart relation(cid:173)
`ship. The spool bottom end 16 includes a bottom flange 22
`which is adapted for fluid tight connection with a top end of 25
`a BOP or a casing spool, as will be explained below in
`further detail. The spool top end 14 includes a top flange 24
`which is adapted for attachment in a fluid tight relationship
`to a high pressure valve or a spool header, as will also be
`explained in more detail below. The top flange 24 is
`connected, preferably by welding or the like, to the inner
`sidewall 18 and the outer sidewall 20 to form an annular
`cavity 26 that preferably extends from the spool bottom end
`16 to the top flange 24. A mandrel 28 having a mandrel top
`end 30 and a mandrel bottom end 32 is received in the
`annular cavity 26 and forcibly reciprocatable within the
`cavity. The mandrel top end 30 preferably has an inverted
`L-shape and extends across the annular cavity 26. A pair of
`0-rings 34 are retained on opposite sides of the mandrel top
`end 30 to provide a fluid resistant seal between the mandrel 40
`28 and the walls of the annular cavity 26 to form an upper
`chamber 36 and a lower chamber 38 of respectively variable
`volumes which change as the mandrel 28 is forcibly recip(cid:173)
`rocated within the annular cavity 26. A step 40 in the annular
`cavity 28 forms a constriction to facilitate sealing the lower
`chamber 38 to inhibit fluid from leakage around the spool
`bottom end 16. Spaced below the step 40 are a pair of
`0-rings 34 retained in the inner surface of the inner sidewall
`18 and the outer sidewall 20. Likewise, positioned adjacent
`the spool bottom end 16 is a second set of 0-rings 34 to
`inhibit the migration of abrasive and corrosive fluids, to
`which the mandrel28 is exposed, into the lower chamber 38.
`Preferably, the mandrel 28 is dimensioned in length so that
`when the mandrel top end 30 is reciprocated to a top of the
`chamber 26, the mandrel bottom end 32 is positioned above 55
`the set of 0-rings 34 adjacent the bottom wall16 to permit
`those 0-rings to be changed because they are the set of
`0-rings most prone to wear due to their exposure to corro(cid:173)
`sive and/or abrasive substances. An internal thread connec-
`tor 42 on the mandrel bottom end 32 is adapted for the 60
`connection of mandrel extension sections having the same
`diameter as the diameter of the mandrel 28. The extension
`sections (not illustrated) permit the mandrel28 to be length(cid:173)
`ened in case a header spool (not illustrated) or the like is
`located between the mandrel 28 and a BOP to be protected. 65
`The connector 42 may likewise be an external thread, or any
`other type of secure connecting arrangement.
`
`6
`The outer sidewall 20 of the spool 12 further includes a
`first port 44 for injecting pressurized fluid into the upper
`chamber 36 of the annular cavity 26 to forcibly stroke the
`mandrel28 downwardly. The outer sidewall20 also includes
`5 a second port 46 for injecting pressurized fluid into the lower
`chamber 38 to stroke the mandrel upwardly in the annular
`cavity 26. Attached to a top surface of the top mandrel end
`30 is a rib 48 which acts as a spacer to ensure that when the
`mandrel is at the top of its stroke, pressurized fluid can be
`10 injected into the cavity 26 to stroke the mandrel down(cid:173)
`wardly. A corresponding rib 48 is located on the bottom
`surface of the mandrel top end 30 and serves the same
`purpose. In order to stroke the mandrel upwardly and
`downwardly, pressurized fluid lines are connected to the first
`15 port 44 and the second port 46. The pressurized fluid is
`preferably a hydraulic fluid but may also be, for example,
`compressed air. If hydraulic fluid is used for stroking the
`mandrel upwardly and downwardly in the annular cavity 26,
`a small hydraulic hand pump may be used or hydraulic pump
`20 lines may be connected to the first port 44 and the second
`port 46. In either case, pressurized fluid is introduced into
`one port and fluid is drained from the other port as the
`mandrel is stroked upwardly or downwardly in the annular
`cavity 26.
`FIG. 2 shows the BOP protector 10 in accordance with the
`invention mounted to a BOP 50 which is in turn connected
`to a well casing 52 by various casing headers and hangers,
`well known in the art. The BOP 50 is a piece of wellhead
`equipment that is well known in the art and its construction
`30 and function do not form a part of this invention. The BOP
`50 and related spools and hangers are therefore shown
`schematically and are not described. Mounted above the
`BOP protector 10 is a high pressure valve 54. The high
`pressure valve 54 is preferably a hydraulically operated
`35 valve having a pressure rating that is at least as high as the
`pressure rating of the BOP 50, and a passage 56 having a
`diameter that is at least as large as the internal diameter of
`the casing 52 to permit oil and gas well servicing tools to be
`inserted through the valve 54 and into the well casing 52.
`As is apparent, the inner sidewall18 of the BOP protector
`10 has an internal diameter which is substantially equal to
`the diameter of the casing 52. As shown in FIG. 2, the
`mandrel 28 has been stroked downwardly through the BOP
`50 and the well is ready to be serviced. The annular passage
`45 defined by the inner sidewall18 of the BOP protector 10 and
`the casing 52 is unrestricted so that tools such as perforating
`guns, plug setters, logging tools, fishing tools and the like
`may be inserted through the BOP protector 10 and into the
`casing 52. This permits wells with more than one production
`50 zone to be serviced without interruption which is a distinct
`advantage over prior art casing savers and well casing
`packers that restrict access to the casing due to a constriction
`of the diameter of the passage between a high pressure valve
`54 and the casing 52.
`The invention also provides a method of fracturing or
`stimulating a well having a blowout preventer 50 located
`above the casing 52 using the BOP protector 10 in accor(cid:173)
`dance with the invention. In accordance with the method, the
`BOP protector 10 is mounted above the BOP 50 and a high
`pressure valve 54 is mounted above the BOP protector 10.
`The high pressure valve 54, commonly called a "frac" valve,
`is well known in the art and its structure and function will
`not be further explained. A high pressure line (not
`illustrated) is connected to the high pressure valve and
`pressurized fluid is pumped into the BOP protector 10 while
`the BOP 50 is still closed to ensure that a fluid tight seal
`exists between the BOP 50 and the BOP protector 10, as well
`
`

`

`5,819,851
`
`7
`as between the BOP protector 10 and the high pressure valve
`54. If no pressure leaks are detected between the spool top
`end 14 or the spool bottom end 16 of the spool12, the high
`pressure valve 54 is closed and the BOP 50 is fully opened.
`Pressurized fluid is injected through the first port 44 using a 5
`pneumatic or hydraulic line attached to that port, and drained
`from the second port 46 using a pneumatic or hydraulic line.
`The pressurized fluid strokes the mandrel 28 down through
`the BOP 50. When the mandrel 28 reaches a bottom of its
`stroke, the pressure in the pressurized fluid injected into the
`first port 44 rises dramatically to indicate that the mandrel28
`has reached the bottom of its stroke and the well is ready for
`servicing. Stimulation or fracturing of the well may then
`commence by pumping abrasive and/or corrosive fluids
`through a high pressure line (not illustrated) attached to the
`high pressure valve 54.
`If the well being serviced has several production zones,
`the stimulation process may proceed sequentially from zone
`to zone because tools such as logging tools, perforating
`guns, plug setters and other well servicing tools (not
`illustrated) can be introduced through the high pressure
`valve 54 and inserted directly into the well casing 52 without
`removing the BOP protector 10. In general, multi-zone wells
`are stimulated one production zone at a time from the bottom
`of the well up. This is usually accomplished in a sequence
`which includes logging the production zone; inserting a plug
`in the casing at a bottom of the production zone; perforating
`the casing in the area of the production zone, if necessary;
`stimulating the production zone by fracturing and/or acidiz(cid:173)
`ing or the like; and, flowing back the stimulation fluids 30
`before recommencing the process for the next production
`zone. The ability to perform all these operations with the
`BOP protector 10 in place greatly facilitates well service
`operations and contributes significantly to the economy of
`servicing wells. After the last production zone of a well has 35
`been serviced, the fracturing and/or stimulating fluids may
`be flowed back through the high pressure valve 54 before the
`BOP protector 10 is removed from the BOP 50 or after the
`BOP protector 10 is removed from the BOP 50, as the
`operator chooses. In either case, when the BOP protector 10 40
`is no longer needed, the mandrel 28 is stroked upwardly out
`of the BOP 50 by injecting pressurized fluid into the second
`port 46 while draining it from the first port 44 until a
`dramatic rise in the resistance to the injected pressurized
`fluid indicates that the mandrel28 is completely stroked out 45
`of the BOP 50. The BOP 50 is then closed, the high pressure
`valve 54 is removed from the top of the BOP protector 10
`and the BOP protector 10 is removed from the BOP 50. A
`wellhead or other terminating equipment can then be
`mounted to the BOP 50 and normal hydrocarbon production 50
`can commence or resume. Since the mandrel28 protects the
`BOP 50 from direct contact with abrasive and/or corrosive
`fluids used during the well stimulation process, the BOP 50
`is not damaged and there is no risk that the blind rams or the
`tubing rams of the BOP 50 will be "washed out" by the 55
`abrasive action of a high volume of proppants pumped into
`the well. Since damage to BOPs is eliminated and the risk
`of having to kill or plug the well before and after treatment
`is obviated, the present invention contributes significantly to
`the economy of well stimulation treatments conducted at 60
`moderate fluid pressures.
`FIG. 3 shows a cross-sectional view of the BOP protector
`12 and two preferred extensions for adapting the BOP
`protector 10 for service in well treatments up to pressures
`which approach the burst pressure of the well casing 52 65
`(about 15,000 psi). In the preferred embodiment a mandrel
`extension 58 is threadedly connected to a bottom end 32 of
`
`8
`the mandrel 28 using a threaded connector 60 at a top end
`62 of the mandrel extension 58. An extension bottom end 64
`of the mandrel extension 58 includes a threaded connector
`66 that is used to connect a mandrel packoff assembly 68,
`which will be described below in more detail. High pressure
`0-ring seals 70, well known in the art, provide a high
`pressure fluid seal in the threaded connectors between the
`mandrel 28, the mandrel extension 58 and the mandrel
`packoff assembly 68. The mandrel28, the mandrel extension
`10 58 and the mandrel packoff assembly 68 are each made from
`4140 steel, a steel which is commercially available, has a
`high tensile strength and a Burnell hardness of about 300.
`Consequently, they are adequately robust to withstand
`extreme pressures of up to 15,000 psi. In order to support a
`15 packoff gasket 78, however, the walls of the mandrel packoff
`assembly 68 are preferably about 1.75" (4.45 em) thick. As
`will be explained below with reference to FIG. 4, it is
`preferable that the wall thickness of the mandrel packoff
`assembly 68 be such that it fits closely within the tubing
`20 head 82 of a well being treated.
`The mandrel packoff assembly 68 includes a packoff
`upper end 72 and a pack off lower end 74. The packoff upper
`end includes a threaded connector 76 which engages the
`threaded connector 66 on the extension bottom end 64 of the
`25 mandrel exten