c12) c19) ccA) Demande-Application
`
`CI P 0
`
`CANADIAN INTELLECTUAL
`
`PROPERTY OFFICE
`
`(21) (Al) 2,195,118
`(22) 1997/01/14
`(43) 1998/07/14
`
`0 PI C
`
`OFFI CE DE LA PROPRIETE
`
`INT ELLECTUELLE DU CANADA
`
`(72) Dallas, Murray L., US
`(71) Dallas, Murray L., US
`(51) Int.Cl. 6 E21B 33/06, E21B 43/25
`(54) DISPOSITIF DE PROTECTION POUR BLOCS OBTURA TEURS
`DE PUITS DE GAZ OU DE PETROLE ET METHODE POUR
`SON UTILISATION DURANT LES OPERA TIO NS DE
`STIMULATION HAUTE PRESSION
`(54) BLOWOUT PREVENTER PROTECTOR AND METHOD OF
`USING SAME DURING HIGH PRESSURE OIL AND GAS
`WELL STIMULATION
`
`42
`
`(57) La presente invention se rapporte a un dispositif
`destine a proteger les blocs obturateurs de puits durant
`les operations de fracturation ou de stimulation de puits.
`Le dispositif comporte un corps creux dont les parois
`interieure et exterieure definissent un espace annulaire.
`Un mandrin insere dans le corps creux peut etre contraint
`de se deplacer dans un mouvement altematif. Le mandrin
`comporte un joint annulaire a sa partie inferieure, lequel
`assure l'etancheite de la liaison mecanique avec un
`guide-foret monte a la pa1tie superieure du cuvelage. Le
`dispositif est monte au-dessus d'un bloc obturateur
`raccorde au support de cuvelage du puits avant le debut
`
`(57) 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
`
`l+I lndustrie Canada
`
`Industry Canada
`
`GREENE’S ENERGY 1003
`
`000001
`
`

`
`0 PI C
`
`O FF ICE DE LA PROPR I ETE
`
`IN TELLECTUELLE DU C ANA DA
`
`CI P 0
`
`C ANA D IAN IN TELLECTUA L
`
`PROPE RTY O FF ICE
`
`(21) (Al) 2,195,118
`(22) 1997/01/14
`(43) 1998/07/14
`
`des operations de stimulation. Le mandrin est descendu a
`travers le bloc obturateur pour proteger celui-ci contre la
`pression fluidique et de l' action corrosive et abrasive des
`fluides de stimulation du puits, en particulier contre les
`pressions extremes et les agents de soutenement abrasifs.
`Le dispositif propose pour proteger les blocs obturateurs
`de puits presente l' avantage de la simplicite d'utilisation
`et assure libre acces au cuvelage du puits aux outils
`employes dans les operations de stimulation qui sont
`realisees a des pressions approchant le point de rnpture
`nominal du cuvelage du puits.
`
`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.
`
`l+I lndustrie Canada
`
`Industry Canada
`
`000002
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`

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`2195118
`
`25
`
`Abstract of the Disclosure
`
`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
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`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
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`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.
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`000003
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`

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`2195t 18
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`BLOWOUT PREVENTER PROTECTOR AND METHOD OF USING
`
`SAME DURING IDGH PRESSURE OIL AND GAS WELL STIMULATION
`
`TECHNICAL FIELD
`
`5
`
`The present invention relates to equipment for servicing oil and gas wells
`
`and, in particular, to apparatus for protecting 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 gas wells using same.
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`10
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`BACKGROUND OF THE INVENTION
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`The servicing of oil and gas wells to stimulate production requires the
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`pumping of fluids under high pressure. The fluids are generally corrosive and/or
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`abrasive because they are frequently laden with corrosive acids and/or abrasive
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`proppants such as sharp sand. Some hydrocarbon producing formations require
`
`15
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`stimulation at extreme pressures to break up the formation and improve the flow of
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`hydrocarbons to the well. If such wells are equipped with a wellhead, it is
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`advantageous to use specialized tools called wellhead isolation tools which are
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`inserted through the wellhead and related equipment to isolate pressure sensitive
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`components from the extreme pressures required to stimulate those wells. Wellhead
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`20
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`isolation tools are taught, for example, in United States Patents 4,867,243, 5,332,044
`
`and 5,372,202 which issued to the applicant respectively on September 19, 1989, July
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`26, 1994 and December 13, 1994.
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`In other wells, stimulation to improve production can be accomplished at
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`more moderate pressures which may be safely contained by blowout preventers
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`25
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`(BOPs) attached to the well casing. In those instances, some operators remove the
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`wellhead equipment and pump stimulation fluids directly through a valve attached to
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`the BOPs. This procedure is adopted to minimize expense and to permit full access
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`to the well casing with tools such as logging tools, perforation guns and the like
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`during the well servicing operation. When pumping abrasive fluids into a well, the
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`30
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`pump rate must be kept high to place the proppant without "screening out," in which
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`a blockage occurs and all the equipment including the high pressure lines are blocked
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`with abrasives injected under high pressure. When the pump rate is high or large
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`quantities of proppant are pumped, the BOPs may be damaged by the cutting action
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`000004
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`

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`2
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`of the proppant. If high rates of abrasive proppant are pumped through a BOP, the
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`blind rams of the BOP or the valve gates can be "washed out" so that the BOP
`
`becomes inoperable.
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`In addition to wellhead isolation tools, casing savers are also used to protect
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`5
`
`wellhead equipment from extreme pressures and well stimulation fluids. Casing
`
`packers as described in United States Patent 4,939,488 which issued February 19,
`
`1991 to McLeod have likewise been used. While casing savers and packers are
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`useful in protecting wellhead equipment including BOPs, they have the disadvantage
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`of restricting access to the casing because they constrict the through bore diameter
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`10
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`from the high pressure valve to the casing. This restricts flow which can limit the
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`pump rate. It also interferes with running servicing tools such as perforating guns,
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`plug setters, or other such tools into the casing. It is advantageous to be able to run
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`tools during well servicing operations so that multi-zone wells can be serviced in a
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`single set without changing the wellhead or wellhead isolation equipment.
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`15
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`Furthermore, the well casing packer taught by McLeod can only be set in a well
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`which is not under pressure at the beginning or end of a servicing operation. It
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`cannot be used in wells with any natural pressure, and is therefore very limited in its
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`utility.
`
`If stimulation treatments are to exceed pressures at which the wellhead
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`20
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`equipment is rated, a wellhead isolation tool, a casing saver or a casing packer have
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`to date been the only tools available for isolating the wellhead from extreme pressure
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`and abrasion. Although it is not uncommon for certain wells to be stimulated at
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`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
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`25
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`(usually in the range of 10,000-15,000 psi) for production stimulation. If the
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`stimulation pressures are in the moderate range of 5,000 psi or less, well stimulation
`
`can be accomplished directly through the BOPs, but unless the BOPs are protected
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`from the abrasive and/or corrosive fluids used in the stimulation processes, there is
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`considerable risk that the BOPs will be damaged and may be damaged to an extent
`
`30
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`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 must be
`
`protected from the pressure as they are not constructed to contain extreme pressures.
`
`000005
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`

`
`219 51 18
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`3
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`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 permits the use of downhole tools which are
`
`often required, or at least very advantageously used, during a stimulation treatment.
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`5
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`If a downhole tool is required during a stimulation treatment using a tree saver, a
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`casing saver or casing packer, it must be pulled before the tool can be inserted into
`
`the casing. This is time consuming and expensive for the well owner who must
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`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
`
`10
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`well casing be provided whenever a stimulation 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,
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`abrasive proppants and/or corrosive stimulation fluids.
`
`It is a further object of the invention to provide a protector for a BOP
`
`15
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`which protects the BOP from well stimulation pressures and fluids without restricting
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`access to the well casing so that well servicing tools such as perforating guns, plug
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`setters, logging tools or other related equipment can be run into and out of the well
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`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
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`20
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`which is simple to manufacture, easy to use and capable of containing even extreme
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`well stimulation pressures.
`
`It is still a further object of the invention to provide a method of stimulating
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`wells using high pressures while protecting a BOP mounted to a top of the well from
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`exposure to excessive pressures and abrasive and/or corrosive fluids.
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`25
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`SUMMARY OF THE INVENTION
`
`These and other objects of the invention are realized in an apparatus for
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`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
`
`30
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`stimulate production, comprising:
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`a spool having a top end, a bottom end, and spaced-apart inner and outer
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`sidewalls that extend between the top end and the bottom end thereof;
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`000006
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`

`
`2195118
`
`4
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`the bottom end being adapted to be mounted above a blowout preventer;
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`the top end being adapted for the attachment of another spool or a valve;
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`a mandrel having a top end and a bottom end, the top end being received in
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`an annular cavity between the inner and outer sidewalls and forcibly reciprocatable
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`5
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`within the cavity, and the bottom end including annular sealing means for high
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`pressure sealing engagement with a top end of a casing of the well;
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`whereby, when the spool is mounted above a blowout preventer, the
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`mandrel can be stroked down through the blowout preventer until the annular sealing
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`means sealingly engages a top end of the casing to isolate the blowout preventer and
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`10
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`protect it from exposure to fluid pressure as well as abrasive and/or corrosive fluids
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`during well stimulation treatments, and stroked up out of the blowout preventer after
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`the well has been stimulated.
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`In accordance of a further aspect of the invention, there is provided a
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`method of fracturing or stimulating a well having at least one blowout preventer
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`15
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`attached to a casing of the well, comprising the steps of:
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`a) mounting above the blowout preventer an apparatus for protecting the
`
`blowout preventer from exposure to fluid pressure as well as abrasive and/or
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`corrosive fluids during the well fracturing and/or stimulation treatment to stimulate
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`production, the apparatus comprising a protector spool having a top end, a bottom
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`20
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`end, and spaced-apart inner and outer sidewalls that extend between the top end and
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`the bottom end thereof, the bottom end being adapted to be mounted above the
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`blowout preventer; the top end being adapted for the attachment of another spool or
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`valve, and a mandrel having a top end and a bottom end, the top end being received
`
`in an annular cavity between the inner and outer sidewalls and forcibly reciprocatable
`
`25
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`within the cavity, and the bottom end including annular sealing means for high
`
`pressure sealing engagement with a top end of a casing of the well;
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`b) mounting at least one high pressure valve above the apparatus;
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`c) closing the at least one high pressure valve;
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`e) fully opening the blowout preventer;
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`30
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`f) stroking the mandrel of the apparatus through the blowout preventer until
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`the annular sealing means is in fluid tight sealing engagement with a top of the
`
`casing of the well;
`
`000007
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`

`
`2/95f 18
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`5
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`g) stimulating or fracturing the well by pumping high pressure fluids and/or
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`proppants through the at least one high pressure valve and the apparatus into the
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`casing of the well using at least one high pressure valve attached to the at least one
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`high pressure valve;
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`5
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`h) stroking the mandrel out of the blowout preventer;
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`i) closing the blowout preventer;
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`j) bleeding off the fluid pressure in the at least one high pressure line;
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`k) removing the at least one high pressure line; and
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`1) removing the apparatus and the at least one high pressure valve.
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`10
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`The apparatus in accordance with the invention comprises a spool which
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`may be mounted above a blowout preventer that is mounted either directly or
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`indirectly to a surface casing spool. The spool includes inner and outer concentric
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`walls which are spaced apart to form an annular cavity that accommodates a mandrel
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`15
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`having a top end that is forcibly reciprocatable within the cavity using fluid pressure,
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`and a bottom end which includes a sealing means for sealingly engaging a top end of
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`a casing of the well. In a preferred embodiment of the invention, the sealing means
`
`is an annular sealing body of plastics or rubber material bonded to the bottom end of
`
`an extension for the mandrel.
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`In the preferred embodiment, the sealing means is
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`20
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`adapted to abut a bit guide surrounding a top end of the casing and to seal against it.
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`A top end of the spool in accordance with the invention is adapted for the attachment
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`of a high pressure valve, a spool header, or a valve spool through which well
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`stimulation fluids can be pumped, and an adapter spool or a union such as a thread
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`half or a Bowen union through which wireline, coil tubing or service tools can be
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`25
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`run.
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`The spool in accordance with the invention for protecting BOPs can
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`therefore be used in a novel method of servicing wells which permits tools such as
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`logging tools, perforating guns, plugs, plug setting tools, fishing tools and related
`
`equipment to be used during the well servicing operation, thus permitting the
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`30
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`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 taken
`
`down for each production zone of a multi-zone well. The spool in accordance with
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`000008
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`

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`2195118
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`6
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`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
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`that has a tubing pin machined into it. This permits a tubing string to be hung
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`through the complete wellhead assembly. The tubing string may be a production
`
`5
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`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
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`stimulation treatment. In that case, well stimulation fluids are pumped through the
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`high pressure valve spool which preferably includes at least two high pressure ports.
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`If coil tubing is used, the top end of the coil tubing is preferably protected from
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`10
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`abrasion by a length of "blast joint" that surrounds the tubing to prevent erosion.
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`Alternatively, a Bowen union can be fitted to a top of the adapter spool to permit
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`wireline, perforating guns, plug setters or other tools to enter the wellhead without
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`obstruction. Or, a high pressure valve can be mounted to the adapter flange so that
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`high pressure fluids can be pumped through up to three ports simultaneously to
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`15
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`permit very high volume injections into the well.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`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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`20
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`FIG. 1 shows a longitudinal cross-sectional view of a blowout preventer
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`protector in accordance with the invention, showing the mandrel in a partially
`
`stroked-out position; and
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`FIG. 2 shows a cross-sectional view of the blowout preventer protector
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`shown in FIG. 1 attached to a blowout preventer on a wellhead and in a position for
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`25
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`performing well stimulation procedures;
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`FIG. 3 is a cross-sectional view of a blowout preventer protector in
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`accordance with another embodiment of the 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 treatments;
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`30
`
`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 preventer in a position for a well stimulation treatment.
`
`000009
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`

`
`7
`
`2l95l [8
`
`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
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`string for monitoring downhole pressures during well stimulation treatments.
`
`5
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`DETAILED DESCRIPTION OF THE 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 spool 12 having a top end 14 and
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`a bottom end 16 with an inner sidewall 18 and an outer sidewall 20 arranged in a
`
`10
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`space-apart relationship. The bottom end 16 includes a bottom flange 22 which is
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`adapted for fluid tight connection with a top end of a BOP or a casing spool, as will
`
`be explained below in further detail. The top end 14 includes a top flange 24 which
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`is adapted for attachment in a fluid tight relationship to a high pressure valve or a
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`spool header, as will also be explained in more detail below. The top flange 24 is
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`15
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`connected, preferably by welding or the like, to the inner sidewall 18 and the outer
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`sidewall 20 to form an annular cavity 26 that preferably extends from the bottom end
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`16 to the top flange 24. A mandrel 28 having a top end 30 and a bottom end 32 is
`
`received in the annular cavity 26 and forcibly reciprocatable within the cavity. The
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`top end 30 of the mandrel 28 preferably has an inverted L-shape and extends across
`
`20
`
`the annular cavity 26. A pair of 0-rings 34 are retained on opposite sides of the top
`
`end 30 of the mandrel 28 to provide a fluid resistant seal between the mandrel 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 reciprocated within the annular cavity 26. A step 40 in the annular cavity
`
`25
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`28 forms a constriction to facilitate sealing the lower chamber 38 to inhibit fluid
`
`from leakage around the bottom end 16 of the spool 12. Spaced below the step 40
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`are a pair of 0-rings 34 retained in the inner surface of the inner sidewall 18 and the
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`outer sidewall 20. Likewise, positioned adjacent the bottom end 16 is a second set
`
`of 0-rings 34 to inhibit the migration of abrasive and corrosive fluids, to which the
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`30
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`mandrel 28 is exposed, into the lower chamber 38. Preferably, the mandrel 28 is
`
`dimensioned in length so that when the top end 30 of the mandrel is reciprocated to
`
`a top of the chamber 26, the lower end 32 of the mandrel is positioned above the set
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`000010
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`2\95118
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`8
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`of 0-rings 34 adjacent the bottom wall 16 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
`
`corrosive and/or abrasive substances. An internal thread connector 42 on the bottom
`
`end 32 of the mandrel 28 is adapted for the connection of mandrel extension sections
`
`5
`
`having the same diameter as the diameter of the mandrel 28. The extension sections
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`(not illustrated) permit the mandrel 28 to be lengthened in case a header spool (not
`
`illustrated) or the like is located between the mandrel 28 and a BOP to be protected.
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`The connector 42 may likewise be an external thread, or any other type of secure
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`connecting arrangement.
`
`10
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`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
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`forcibly stroke the mandrel 28 downwardly. The outer sidewall 20 also includes a
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`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 end
`
`15
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`30 of the mandrel 28 is a rib 48 which acts as a spacer to ensure that when the
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`mandrel is at the top of its stroke, pressurized fluid can be injected into the cavity 26
`
`to stroke the mandrel downwardly. A corresponding rib 48 is located on the bottom
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`surface of the top end of the mandrel 28 and serves the same purpose. In order to
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`stroke the mandrel upwardly and downwardly, pressurized fluid lines are connected
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`20
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`to the first port 44 and the second port 46. The pressurized fluid is preferably a
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`hydraulic fluid but may also be, for example, compressed air. If hydraulic fluid is
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`used for stroking the mandrel upwardly and downwardly in the annular cavity 26, a
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`small hydraulic hand pump may be used or hydraulic pump lines may be connected
`
`to the first port 44 and the second port 46. In either case, pressurized fluid is
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`25
`
`introduced into one port and fluid is drained from the other port as the mandrel is
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`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
`
`30
`
`wellhead equipment that is well known in the art and its construction 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
`
`000011
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`2195118
`
`9
`
`protector 10 is a high pressure valve 54. The high pressure valve 54 is preferably a
`
`hydraulically operated 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
`
`5
`
`tools to be inserted through the valve 54 and into the well casing 52.
`
`As is apparent, the inner sidewall 18 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 defined by the inner
`
`10
`
`sidewall 18 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 zone to be serviced without interruption which is a
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`distinct advantage over prior art casing savers and well casing packers that restrict
`
`15
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`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 accordance with the invention. In accordance with the method, the BOP
`
`20
`
`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
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`explained. A high pressure line (not illustrated) is connected to the high pressure
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`valve and pressurized fluid is pumped into the BOP protector 10 while the BOP 50 is
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`still closed to ensure that a fluid tight seal exists between the BOP 50 and the BOP
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`protector 10, as well as between the BOP protector 10 and the high pressure valve
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`54. If no pressure leaks are detected between the top end 14 or the bottom end 16 of
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`the spool 12, the high pressure valve 54 is closed and the BOP 50 is fully opened.
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`Pressurized fluid is injected through the first port 44 using a pneumatic or hydraulic
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`line attached to that port, and drained from the second port 46 using a pneumatic or
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`hydraulic line. The pressurized fluid strokes the mandrel 28 down through the BOP
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`50. When the mandrel 28 reaches a bottom of its stroke, the pressure in the
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`pressurized fluid injected into the first port 44 rises dramatically to indicate that the
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`mandrel 28 has reached the bottom of its stroke and the well is ready for servicing.
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`Stimulation or fracturing of the well may then commence by pumping abrasive
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`and/or corrosive fluids through a high pressure line (not illustrated) attached to the
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`high pressure valve 54.
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`If the well being serviced has several production zones, the stimulation
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`process may proceed sequentially from zone to zone because tools such as logging
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`tools, perforating guns, plug setters and other well servicing tools (not illustrated) can
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`be introduced through the high pressure valve 54 and inserted directly into the well
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`casing 52 without removing the BOP protector 10. In general, multi-zone wells are
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`stimulated one production zone at a time from the bottom of the well up. This is
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`usually accomplished in a sequence which includes logging the production zone;
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`inserting a plug in the casing at a bottom of the production zone; perforating the
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`casing in the area of the production zone, if necessary; stimulating the production
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`zone by fracturing and/or acidizing or the like; and, flowing back the stimulation
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`fluids before recommencing the process for the next production zone. The ability to
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`perform all these operations with the BOP protector 10 in place greatly facilitates
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`well service operations and contributes significantly to the economy of servicing
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`wells. After the last production zone of a well has been serviced, the fracturing
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`and/or stimulating fluids may be flowed back through the high pressure valve 54
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`before the BOP protector 10 is removed from the BOP 50 or after the BOP protector
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`10 is removed from the BOP 50, as the operator chooses. In either case, when the
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`BOP protector 10 is no longer needed, the mandrel 28 is stroked upwardly out of the
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`BOP 50 by injecting pressurized fluid into the second port 46 while draining it from
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`the first port 44 until a dramatic rise in the resistance to the injected pressurized fluid
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`indicates that the mandrel 28 is completely stroked out of the BOP 50. The BOP 50
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`is then closed, the high pressure valve 54 is removed from the top of the BOP
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`protector 10 and the BOP protector 10 is removed from the BOP 50. A wellhead or
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`other terminating equipment can then be mounted to the BOP 50 and normal
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`hydrocarbon production can commence or resume. Since the mandrel 28 protects the
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`BOP 50 from direct contact with abrasive and/or corrosive fluids used during the
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`well stimulation process, the BOP 50 is not damaged and there is no risk that the
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`blind rams or the tubing rams of the BOP 50 will be "washed out" by the abrasive
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`action of a high volume of proppants pumped into the well. Since damage to BOPs
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`is eliminated and the risk of having to kill or plug the well before and after treatment
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`is obviated, the present invention contributes significantly to the economy of well
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`stimulation treatments conducted at moderate fluid pressures.
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`Fig. 3 shows a cross-sectional view of the BOP protector 12 and two
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`preferred extensions for adapting the BOP protector 10 for service in well treatments
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`up to pressures which approach the burst pressure of the well casing 52 (about
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`15,000 psi). In the preferred embodiment a mandrel extension 58 is threadedly
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`10
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`connected to a bottom end 32 of the mandrel 28 using a threaded connector 60 at a
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`top end 62 of the mandrel extension 58. A bottom end 64 of the mandrel extension
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`58 includes a threaded connector 66 that is used to connect a mandrel packoff
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`assembly 68, which will be described below in more detail. High pressure 0-ring
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`seals 70, well known in the art, provide a high pressure fluid seal in the threaded
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`15
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`connectors between the mandrel 28, the mandrel extension 58 and the mandrel
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`packoff assembly 68. The mandrel 28, the mandrel extension 58 and the mandrel
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`packoff assembly 68 are each made from 4140 steel, a steel which is commercially
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`available, has a high tensile strength and a Burnell hardness of about 300.
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`Consequently, they are adequately robust to withstand extreme pressures of up to
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`20
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`15,000 psi. In order to support a packoff gasket 78, however, the walls of the
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`mandrel packoff assembly 68 are preferably about 1.75 " (4.45 cm) thick. As will be
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`explained below with reference to FIG. 4, it is preferable that the wall thickness of
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`the mandrel packoff assembly 68 be such that it fits closely within the tubing head
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`82 of a well being treated.
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`The mandrel packoff assembly 68 includes an upper end 72 and a lower end
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`74. The upper end includes a threaded connector 76 which engages the threaded
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`connector 66 on the lower end 64 of the mandrel extension 58. The lower end 74 of
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`the mandrel packoff assembly 68 includes the annular seal 78 which sealingly
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`engages a top of the well casing as will be described below with reference to Fig. 4.
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`30
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`The annular seal 78 is preferably a thermoplastic or a synthetic rubber seal that is
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`bonded directly to the lower end 74 of the mandrel packoff assembly 68. The lower
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`end 74 of the mandrel packoff assembly 68 is preferably machined to provide a
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`bearing surface to which the annular seal 78 may be bonded. As described above,
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`the annular seal 78 is preferably made from a thermoplastic such as polyurethane or
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`a rubber compound such as nitryl rubber. The annular seal 78 should have a
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`hardness of about 80 to about 100 durometer. Experimentation has shown that either
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`5
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`polyurethane or nitryl rubber in that hardness range is capable of providing a secure
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`seal that will withstand up to at least about 15,000 psi if it is properly bonded to a
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`mandrel packoff as