Abstract:
An apparatus ( 100 ) and method for removably mounting a lubricator assembly ( 106 ) to a component of the wellhead stack. The component of the wellhead stack is an annular blowout preventer (BOP) ( 50 ). Tool and communication conduit lubrication and access to the wellbore without requiring activation of the packing element of the BOP ( 50 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Well drilling operations are typically performed through a long assembly of threadably connected pipe sections called a drillstring. Often, the drillstring is rotated at the surface by equipment on the rig thereby rotating a drill bit attached to a distal end of the drillstring downhole. Weight, usually by adding heavy collars behind the drill bit, is added to urge the drill bit deeper as it is rotated. Because subterranean drilling generates a lot of heat and cuttings as the formation below is pulverized, drilling fluid, or mud, is pumped down to the bit from the surface. 
         [0002]    Typically, drill pipe sections are hollow and threadably engage each other such that the bores of adjacent pipe sections are hydraulically isolated from the “annulus” formed between the outer diameter of the drillstring and the inner diameter of the wellbore (either cased or as-drilled). Drilling mud is then typically delivered to the drill bit through the bore of the drillstring where it is allowed to lubricate the drill bit through ports and return with any drilling cuttings through the annulus. Because the drillstring and wellbore are often several thousand feet in depth, a tremendous amount of pressure is required to pump the drilling mud down to the bit and back up to the surface in a complete cycle. It is not unheard of for drilling mud pressures to exceed 20,000 pounds per square inch at these depths. Because of safety concerns, a device called an annular blowout preventer (“BOP”) is often used. The annular BOP is used to seal the gap in the annulus between the drillstring and the borehole in the event of a downhole “kick” attributed to a gas pocket or other subterranean event. The annular BOP is designed to be quickly activated to prevent such kicks from spewing wellbore fluids and hazardous gasses into the atmosphere at the well site. 
         [0003]    Frequently, measurements of formation density, porosity, and permeability are taken before a well is drilled deeper or before a change in drilling direction is made. Often, measurements relating to directional surveying are needed to ensure the wellbore is being drilled according to plan. These measurements and operations can be performed with a measurement while drilling assembly (MWD), whereby the measurements are made in real-time at or proximate to the drill bit and subsequently transmitted to operators at the surface through mud-pulse or electromagnetic-wave telemetry. While MWD operations are possible much of the time, manual measurements are often desired either for verification purposes, or the measurements desired are not within the capabilities of the MWD system. For this reason, measurements are often required by “wireline” or other devices absent the presence of the drillstring. Various tools, communications conduits, and method are used in the oilfield today to perform measurements or other operations. 
         [0004]    For the purpose of this disclosure, the term “tool” is generic and may be applied to any device sent downhole to perform any operation or measurement. Particularly, a downhole tool can be used to describe a variety of devices and implements to perform a measurement, service, or task, including, but not limited to, pipe recovery, formation evaluation, directional measurement, and workover. Furthermore, the term communications “conduit,” while frequently thought of by the lay person as a tubular member for housing electrical wires, in oilfield parlance, is used to describe anything capable of transmitting fluid, force, electrical, or light communications from one location (e.g. surface) to another (e.g. downhole). For this reason, the term conduit, as applied with respect to the present disclosure includes, but is not limited to, wireline, slick line, fiber optic cable, and any present or future equivalents thereof. 
         [0005]    Therefore, a need exists for a device and method to allow a variety of tools and communications conduits to enter a pressurized wellbore to perform operations and take measurements. The device would preferably be capable of being quickly and easily removed when not needed and would be configured to attach to a component of the wellhead stack, including, but not limited to, annular BOP&#39;s, ram-type BOP&#39;s, and wellhead valves. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The deficiencies of the prior art are addressed by an apparatus to be mounted to a wellhead stack. The apparatus preferably includes a hold-down retainer affixed to a component of the wellhead stack wherein the hold-down retainer includes a locking profile. The apparatus preferably includes a hold-down mandrel having an engagement profile. The engagement profile is preferably configured to be retained by the locking profile when the mandrel is in a locked position. The engagement profile is preferably configured to be axially displaced with respect to the locking profile when the mandrel is in an unlocked position. The apparatus preferably includes a lubricator assembly extending upward from the mandrel. 
         [0007]    The deficiencies of the prior art are also addressed by an apparatus to be mounted to a wellhead stack wherein the hold-down retainer includes a locking profile and a sealing surface. The apparatus preferably includes a hold-down mandrel wherein the mandrel has an engagement profile and a hydraulic seal. The engagement profile is preferably configured to be retained by the locking profile when the mandrel is in a locked position. The engagement profile is preferably configured to be axially displaced with respect to the locking profile when the mandrel is in an unlocked position. The apparatus preferably includes a lubricator assembly extending upward from the mandrel. 
         [0008]    The deficiencies of the prior art are also addressed by a method to attach a communications tool lubricator assembly to a wellhead stack. The method preferably includes attaching a hold-down retainer to a component of the wellhead stack, wherein the retainer includes a locking profile. The method also preferably includes mounting the lubricator assembly to a proximal end of a hold-down mandrel, wherein the mandrel includes an engagement profile on an outer surface. The method preferably includes engaging the mandrel into the retainer, wherein the engagement profile is preferably configured to engage the locking profile and retain the mandrel. The method also preferably includes preventing the escape of borehole fluids from the wellhead stack through the use of a sealing mechanism between the mandrel and the retainer. 
         [0009]    The deficiencies of the prior art are also addressed by an apparatus to allow the insertion of tools through a wellhead stack. The apparatus preferably includes a hold-down retainer secured to the wellhead stack wherein the hold-retainer includes a locking profile. The apparatus preferably includes a mandrel having an engagement profile, wherein the engagement profile is configured to be retained by the locking profile when the mandrel is in a locked position. Preferably, the engagement profile is configured to be removed from the locking profile when the mandrel is in an unlocked position. The apparatus preferably includes a lubricator assembly extending upward from the mandrel, wherein the lubricator is configured to house the tools to be inserted through the wellhead stack. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0010]      FIG. 1  is a schematic profile drawing of a hold-down apparatus in accordance with a preferred embodiment of the present invention, shown engaged with an annular blow out preventer apparatus. 
           [0011]      FIG. 2  is a schematic representation of the hold-down apparatus of  FIG. 1 . 
           [0012]      FIG. 3  is a schematic representation of a hold-down retainer of  FIG. 2 . 
           [0013]      FIG. 4  is a schematic representation of a hold-down mandrel with an attached lubricator of  FIG. 2 . 
           [0014]      FIG. 5  is a schematic representation of the locking mechanism of the hold-down retainer and mandrel of  FIGS. 1-4 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    Referring initially to  FIG. 1 , a hold-down apparatus  100  in accordance with a preferred embodiment of the present invention is shown below a rig floor  10  mounted atop an annular blow out preventer  50 . Annular BOP  50  typically includes a main body  52 , a mounting flange  54 , a packing element  56 , and a compression piston  58 . BOP  50  is mounted atop the wellhead or other equipment (not shown) by bolted flange  54 . Annular BOP serves to seal off the annulus between a pipe or tubing string engaged therethrough and a borehole in the event of a downhole surge in pressure or “kick.” Hydraulic pressure is maintained in BOP  50  to drive piston  58  into packing element  56  to compress it against anything engaged therethrough. In the event of a sudden increase in pressure, BOP  50  can be configured so that piston  58  compresses packing element  56  even tighter as annular pressure increases such that the escape of annular fluids is prevented. 
         [0016]    Referring still to  FIG. 1 , the hold-down apparatus  100  preferably is mounted atop annular BOP  50 . Hold-down apparatus  100  preferably includes a hold-down retainer  102 , a hold-down mandrel  104  with an attached lubricator  106 , a bell nipple  108  with a flowline connection  110 , and a hydraulic packoff device  112 . Hold-down retainer  102  is shown with a bolting flange  114  having a plurality of bolt holes  116  for securing retainer  102  to the top of BOP  50 , but any means well known to those of skill in the art for connecting retainer  102  to a BOP  50  or other wellhead component may also be used, such as quick-connect flanges and the like. A hydraulic seal  118  is preferably provided to prevent the escape of fluids from the interface between BOP  50  and hold-down retainer  102 . From retainer  102 , bell nipple  108  extends upward towards rig floor  10  and provides a flowline connection  110  for the removal of fluids therefrom. Retainer  102  also provides a receptacle  120  wherein hold-down mandrel  104  is engaged and locked into place. Hold-down mandrel  104  preferably includes a lubricator housing  106  and a stinger mandrel  122  attached thereto. 
         [0017]    Lubricator housing  106  can be a tube-shaped body long enough to completely enclose a tool to be engaged within the bore below BOP  50 . Lubricator  106  can include packoff  112  at its top and a pressure regulator  124  to remove pressure or fluids from inside lubricator  106 . Dual packoff systems can also be used where lubricator housing  106  does not completely enclose the tool. Packoff  112  is preferably constructed to allow the “stripping” in and out therethrough of communications conduit (wireline, slickline, fiber optic, etc.) and any tools disposed thereon with little or no bore or well fluids escaping therethrough. However, packoff  112  may also be constructed to only allow communications conduit therethrough, whereby any tools to be used with lubricator  106  are “made up” on the rig floor after the conduit is engaged through packoff  112 . Ideally, the communications conduit (and attached tools) is engaged through packoff  112 , through lubricator  106 , mandrel  104 , stinger  122 , BOP  50 , and into the wellbore below. 
         [0018]    Referring now to  FIG. 2 , a schematic drawing of hold-down assembly  100  is shown. As can be seen more clearly than in  FIG. 1 , hold-down assembly  100  includes hold-down retainer  102 , hold-down mandrel  104 , lubricator assembly  106 , and stinger  122 . Lubricator  106  and stinger  122  are preferably threadably engaged within hold-down mandrel  104  at respective threaded connections  126  and  128 . Threaded connections  126  and  128  are preferably constructed to be high tensile strength sealed connections. 
         [0019]    Referring to  FIGS. 2 and 4 , elastomeric seals  130  and  132  can prevent fluids within bores  134  and  136  of lubricator  106  and stinger  122  from escaping through connections  126  and  128 . Hold-down mandrel  104  preferably includes a seal member  138  and an engagement profile  140  upon an outer surface  142  to enable mandrel  104  to latch into sealing engagement with hold-down retainer  102 . Seal member  138  can provide an integral seal between the hold-down retainer  102  and the hold down mandrel  104 , providing additional leak protection over systems which rely solely on the BOP  50  as the pressure seal. 
         [0020]    Engagement profile  140  is shown including a plurality of aligned locking dogs  144 , and rotation elements  146 . Rotation elements  146  are configured to rotate hold-down mandrel  104  into either a locking or unlocking alignment with hold-down retainer  102 . Angled planes  148  of rotation elements  146  induce a torque into hold-down mandrel  104  when axially loaded, thereby rotating mandrel  104  into alignment. Locking dogs  144  are spaced such that when engaged into hold-down mandrel  104  and locked into position, their shear strength prevents removal of hold-down mandrel  104  therefrom. A seating profile  150  bottoms out and prevents further engagement of mandrel  104  within retainer  102  when properly seated. 
         [0021]    Referring to  FIGS. 2 and 3  together, hold-down retainer  102  includes a locking profile  160  and a seat  162 . Locking profile  160  includes two sets of rotation elements, alignment elements  164 , and locking elements  166 . Profile  160  also includes a plurality of locking dogs  168 . Alignment elements  164  act in conjunction with rotation elements  146  of  FIG. 4  to align locking dogs  144  of mandrel  104  with axial gaps  170  between locking dogs  168  of retainer  102 . Furthermore, hold-down retainer  102  includes a seal bore  172  for sealing engagement with seal  138  of mandrel  104 . Alternatively, seal bore  172  of retainer  102  and seal member  138  of mandrel  104  can be reversed so that seal member  138  is on retainer  102  and a sealing surface is on the periphery of mandrel  104 . Furthermore, specific configurations of seal member  138  and bore  172  can be of any type known by one skilled in the art including, but not limited to, elastomeric seals, metal-to-metal seals, or polymeric seals. 
         [0022]    Referring to  FIGS. 2-5  together, the engagement of hold-down mandrel  104  into hold-down retainer  102  can be described. Hold-down mandrel  104  is engaged within bore  172  of hold-down retainer  102  until rotation elements  146  of mandrel  104  engage alignment elements  164  of retainer  102 . When loaded axially, angled planes  148  of mandrel  104  engage alignment elements  164  and urge rotation of mandrel  104  in direction shown at arrow  174 . Once this rotation is complete, locking dogs  144  of mandrel  104  are aligned with gaps  170  of retainer  102  and mandrel  104  is able to continue engaging bore  172  of hold-down retainer  102  in direction of arrow  176 . As mandrel  104  is engaged further, angled planes  148  of rotation elements  146  engage locking elements  166  of retainer  102 . Like alignment elements  164 , locking elements  166  urge the rotation of mandrel  104  in the rotational direction of arrow  178 . As this locking step is necessary to secure engagement of mandrel  104  into retainer  102  for this particular embodiment for profiles  140  and  160 , external torque in the direction of arrow  178  may need to be applied to mandrel  104  or lubricator  106 . The final rotation of mandrel  104  in direction of arrow  178  when rotation elements  146  engage locking elements  166  rotates locking dogs  144  of mandrel  104  between axial gaps  170  between locking dogs  168  of hold-down retainer  102 . 
         [0023]    With locking dogs  144  and  168  so intertwined, their shear strength is capable of resisting forces that would otherwise separate hold-down mandrel  104  from hold-down retainer  102 . To unlock mandrel  104  from retainer  102 , mandrel  104  is rotated counter to direction arrow  178  and is lifted out of retainer  102  when dogs  144  or mandrel  104  are aligned with gaps  170  between dogs  168  of retainer  102 . 
         [0024]    Hold-down system  100  has many applications and uses. Preferably, hold-down retainer  102  with attached bell nipple  108  and flowline connection  110  are installed atop the annular BOP  50  in the beginning of drilling operations for use with hold-down mandrel  104  at a later time. Alternatively, other designs of BOP&#39;s may be used in place of annular BOP  50 . With retainer  102  and bell nipple  108  in place, operations continue as usual until an entry operation is desired. For a typical wireline operation, mandrel  104 , with lubricator  106  and stinger  122 , can be inserted and locked within the hold-down retainer  102 . Packoff  112  can be removed from the top of lubricator  106 , allowing access to the full bore of lubricator  106 . Wireline can be threaded through packoff  112  and attached to a tool. The tool can then be run through lubricator  106  and packoff  112  reinstalled atop lubricator  106 . 
         [0025]    Usually, to effectuate the installation of lubricator  106  and mandrel  104  into annular BOP  50 , a ram-type BOP (not shown) or other form of shutoff valve is closed below the annular BOP  50 . Then, the activation pressure of annular BOP  50  is relaxed, thus allowing stinger  122  mounted below mandrel  104  to be engaged within packing element  56  of BOP  50 . As stinger  122  engages packing element  56 , profiles  140  and  160  engage one another and mandrel  104  and lubricator  106  are rotated until locking engagement of mandrel  104  with retainer  102  is achieved. Once locked into place, a ram-type BOP or other valve devices below can be opened without the risk of wellbore fluids escaping. Seal  118  at flange  114  of retainer  102  prevents leakage between retainer  102  and BOP  50 . Seal  138  of mandrel  104  prevents leakage between mandrel  104  and retainer  102 . Seals  130  and  132  prevent leakage between mandrel  104  and lubricator  106  and stinger  122 . Finally, packoff  112  atop lubricator  106  prevents leakage around communications conduit. Therefore, the packing element  56  of annular BOP  50  does not need to be energized to prevent the leakage of fluids from the wellbore. With lubricator  106  and mandrel  104  installed within retainer  102 , the tools lubricated within can now be deployed downhole. 
         [0026]    The present invention has several concomitant advantages, two of which are the provision of additional leak protection and the ease of installation. The present invention provides an integral seal between the hold-down retainer and the hold-down mandrel, which adds additional leak protection over systems which rely solely on the BOP as the pressure seal. The lock-down system of the present invention can also allow installation from the rig floor, thereby avoiding the need for an operator to go below the rig floor during installation. 
         [0027]    While a preferred embodiment for the locking mechanism of hold-down assembly  100  is shown, it should be understood by one skilled in the art that departures from the specific embodiment disclosed can still be within the scope and meaning of the invention as claimed. For example, mechanisms that include hydraulic or electrical actuation mechanisms can be used in place of the “inclined plane” system disclosed herein to lock the hold-down mandrel to the hold-down retainer.