Abstract:
The present invention relates to a method and apparatus for the servicing or workover of a hydrocarbon well. The apparatus includes a pair of hydraulic cylinders pivotally mounted to a pair of base beams connected to each other. The cylinders are moveable from a horizontal position for transportation to a vertical position for operation in which position the two cylinders flank a wellhead and are adapted to lift the wellhead and attached production tubing using a workover beam and a lifting sub. The wellhead and production tubing can be rotated as or after they are elevated. A motor may be mounted to the workover beam to rotate the wellhead and the tubing. A calibrated pressure gauge may be used to indicate the weight being lifted. The apparatus can be wheel mounted and towed behind a crane truck. The advantage is a safe, economical and timesaving apparatus for performing jobs that previously required the setup and operation of a workover rig.

Description:
TECHNICAL FIELD 
     The present invention relates to the servicing or workover of hydrocarbon wells and, in particular, to a method and apparatus for the servicing or workover of a hydrocarbon well when tubing does not need to be run into or removed from the well. 
     BACKGROUND OF THE INVENTION 
     Hydrocarbon production wells which are drilled in the earth to produce oil or gas must be reworked or serviced from time to time. Wells may require service for a number of reasons. For example, worn or faulty valves may require replacement, seals may need to be replaced or renewed, or it may be necessary or desirable to insert a new flange or remove a flange from the wellhead, etc. Well workover generally entails well treatments to stimulate hydrocarbon production. Such treatments may include high pressure fracturing and/or acidizing. During well stimulation it is common knowledge that it is preferable to introduce stimulation fluids into the well at the highest possible transfer rate. Consequently, the wellhead is now frequently removed and stimulation fluids are pumped through the blowout preventers and into the casing. In order to protect the blowout preventers, blowout preventer protectors have been invented, as described in Applicant&#39;s U.S. Pat. No. 5,819,851 which issued on Oct. 13, 1998. Generally, a workover rig is brought in and setup to remove the wellhead components when well workover is required. Such rigs comprise a derrick or mast which supports pulleys or block and tackle arrangements operable to pull the wellhead from the well and may also be used to pull the production tubing string from the well bore or run a production tubing string or other tools into the well. 
     The rig is used to remove and replace the wellhead, unseat and reseat the packers and/or anchors in the well, etc. Although workover rigs are functional and adapted to perform any job associated with manipulating well components during a well workover, they are large assemblies of equipment that are expensive to move and setup. Besides, they require a crew of four, so they are expensive to operate. 
     A workover rig may also be brought in for servicing a well to install blowout preventers (BOPs), repair or replace valves or seals, etc. In each of these servicing operations the production tubing is not removed from or run into the well. Nonetheless, the production tubing may have to be lifted with the wellhead. 
     Efforts have been made to develop various types of lifting apparatus for use in well workovers and well servicing operations. In particular, a portable or compact apparatus has been invented for replacing a large conventional well rig for lifting a wellhead and production tubing string in certain well servicing or workover applications. U.S. Pat. No. 4,756,366 which issued to Maroney et al. on Jul. 12, 1988 and is entitled “WELL SERVICING METHODS USING A HYDRAULIC ACTUATED WORKOVER MAST”, discloses a portable workover rig for lowering and raising objects such as pipe into and out of a borehole. The workover rig is mounted to a heavy vehicle and includes a mast which can be raised from a horizontal to a vertical position, a hydraulic system and drum cable system. Nevertheless, the portable workover rig disclosed in this patent is expensive to construct and operate because a dedicate vehicle, a dedicated hydraulic system and a complicated mechanical structure are involved. 
     A tool useful in pulling casing from a dead well is illustrated in U.S. Pat. No. 2,661,063, which issued to Owens on Dec. 1, 1953 and is entitled “METHOD AND MEANS OF PULLING PIPE FROM A WELL”. Owens discloses the use of a pair of hydraulic jacks to loosen a pipe that gets stuck while being pulled from a dead well by a rig. The jacks exert an upward force through two arms affixed to a collar attached by shearable pins to the pipe being pulled by the rig. The pins shear unless the pipe dislodges from the stuck position. The shearing of the pins causes a downward jar or jerk on the pipe that tends to loosen the pipe. After the pipe is loosened, it is pulled from the well using the rig until it is removed, or it gets stuck again. It is apparent that the jacks used in this application are auxiliary and only used in conjunction with a rig. The jacks are not designed to lift a wellhead for well servicing or workover. Nor is the pipe being lifted by the jacks rotatable relative to the collar due to the shearable pin connection between the two. Therefore, this apparatus is not adapted for well servicing or workover. 
     There therefore exists a need for a safe, economical apparatus for well servicing or workover which permits a servicing or workover operation to be rapidly and efficiently accomplished when tubing does not need to be run into or removed from the well. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide an apparatus for lifting a wellhead, a production tubing string, or a wellhead with an attached production tubing string for well servicing or workover. 
     Another object of the invention is to provide an apparatus and method for well servicing or workover in a safe, economical and fast manner when the production tubing does not need to be run into or removed from the well. 
     A further object of the invention is to provide a portable apparatus for lifting a wellhead, a production tubing string or a wellhead with an attached tubing production string. 
     In accordance with one aspect of the invention, there is provided an apparatus for well servicing or workover comprising: 
     a pair of base assemblies connected to each other in a spaced apart relationship adapted to flank a wellhead; 
     a pair of lifting devices respectively mounted to the base assemblies for lifting the wellhead, the wellhead with an attached production tubing string, or a production tubing string; 
     a workover beam supported at opposite ends by the lifting devices; and 
     a lifting sub connected to the workover beam and adapted for detachable connection to the wellhead or the production tubing string so that the wellhead is rotatable when disconnected from the well and the lifting devices are operated to raise the workover beam. 
     The lifting devices are preferably a pair of hydraulic cylinders. Each of the base assemblies preferably comprise a base beam, a plate extending longitudinally of and upwardly from the base beam, and a locking device associated with the plate for releasably retaining the lifting devices in a vertical position. 
     Each of the cylinders is preferably mounted to the plate by a pivotal axis perpendicular to the plate so that the lifting devices are pivotally moveable to a horizontal position for transportation, in which position the lifting devices are parallel to the base beam. The base beams are preferably parallel to each other and interconnected by a plurality of cross-members. The cross-members are preferably permanently affixed to one end of the base beams and detachably connected to the other end of the base beams to permit the apparatus to be positioned so that the base beams flank the wellhead. 
     The lifting sub is preferably rotatable relative to the workover beam so that the wellhead and/or the production tubing string may be rotated while it is attached to the lifting sub. The apparatus may further comprise a motor mounted to the workover beam and associated with the lifting sub to permit the wellhead or a production tubing connected to the lifting sub to be rotated under mechanical force exerted by the motor. 
     In accordance with another aspect of the invention, a method of well servicing or workover comprises: 
     a) placing on a well site an apparatus which includes lifting devices that are respectively supported by a pair of interconnected base assemblies so that the wellhead is flanked by the lifting devices; 
     b) connecting the wellhead to a lifting sub secured to a workover beam supported on opposite ends by the respective lifting devices; 
     c) disconnecting the wellhead at a point required for the well servicing or workover operations; 
     d) raising the workover beam by operating the lifting devices; 
     e) performing the well servicing or workover operations; 
     f) lowering the workover beam by operating the lifting devices after the well servicing or workover operation is completed; 
     g) reconnecting the wellhead and disconnecting the lifting sub from the wellhead; and 
     h) removing the apparatus from the well site. 
     Preferably, step b) is completed by removing a wellhead cap and connecting the lifting sub to a top of the wellhead. 
     The advantageous structure of the apparatus and the method according to the invention provide a simple, safe, fast and economic manner of performing a well service or workover operation, particularly, in the cases in which the production tubing does not need to be run into or removed from the well. The use of hydraulic cylinders as lifting devices also provides a convenient method of calculating the weight of the wellhead, and/or any production tubing that has been lifted. The weight can be calculated using a reading from a pressure gauge that is connected to the service line for supplying hydraulic fluid to the cylinders. 
     The structure of the apparatus is also adapted to facilitate transportation. The apparatus may be constructed as a skid or may be rubber wheel mounted and provided with a hitch to permit towing behind a crane truck or the like. If rubber wheel mounted, the wheels are preferably pivotally mounted to the base beams and rotatable from a transport position to a working position. Hydraulic cylinders may be used to shift the wheels from the transport to the working position. 
     Other features and advantages of the apparatus will be clearly understood from the detailed description of the preferred embodiment which follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in more detail by way of example only and with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic side elevational view of a preferred embodiment of an apparatus in accordance with the invention, illustrating the apparatus with a pair of lifting devices in a horizontal position for transportation; 
     FIG. 2 illustrates the embodiment shown in FIG. 1 in the same view with the lifting devices in a vertical working position; 
     FIG. 3 is a schematic plan view of the embodiment shown in FIG. 1, in a working position over a wellhead; 
     FIG. 4 is a schematic elevational view from a point indicated by arrow A of FIG. 3, illustrating a step in the servicing or workover of a hydrocarbon well using the apparatus shown in FIGS. 2 and 3; 
     FIG. 5 is a schematic elevational view of a workover beam shown in FIG. 4, with a motor mounted thereto to facilitate rotation of a wellhead or a production tubing; 
     FIG. 6 is a schematic side elevational view of the apparatus shown in FIGS. 1-5 equipped with wheels and a tongue to permit the apparatus to be towed to a well site, the wheels being in a lowered position adapted for transport; 
     FIG. 7 is a schematic side elevational view of the apparatus shown in FIG. 6, showing the apparatus in a working position with the wheels raised; and 
     FIG. 8, which appears on sheet one of the drawings, is a schematic diagram of a hydraulic system, showing a pressure gauge which may be used for calculating the weight of a wellhead and/or a production tubing during a well servicing or a workover operation. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in FIGS. 1 and 2, the apparatus of the present invention for well servicing and workover is generally designated by reference numeral  10 . The apparatus  10  includes a pair of spaced apart base assemblies  12  and lifting devices  14 . The lifting device  14  are preferably hydraulic cylinders, but may be ball jacks (not shown) or any other appropriate and robust lifting device. Each base assembly preferably includes an elongated steel base beam  16  which has a rectangular cross-section. A trapezoidal plate  18  extends upwardly from a center portion of the base beam  16  and is affixed to an inner side of the base beam  16 , as more clearly illustrated in FIGS. 3 and 4. A vertical ram support  20  which extends from a top of the base beam  16  to a top edge of the trapezoidal plate  18  supports the lifting device  14  in a vertical working position. The entire base assembly  12  is preferably a welded steel structure. 
     The lifting device  14  is mounted to the outside of the plate  18  by a pivot pin  22  that is located above the base beam  16  adjacent the ram support  20 , so that the lifting device  14  is pivotally moveable from a horizontal position for transport, as shown in FIG. 1, to a vertical position for working, as shown in FIG. 2. A bore  24 , or the like, is provided near a top of the plate  18  for detachably receiving a lock pin  26  that is more clearly illustrated in FIG.  4 . The lifting device  14  is securely supported in the vertical position between the ram support  20  and the lock pin  26 . 
     As illustrated in FIGS. 3 and 4, the pair of base assemblies  12  are interconnected at one end by permanent cross-members  28  which are preferably welded to the base beams  16  and at the other end by detachable cross-members  30  which are detachably connected to the base beams  16  using connector pins  32 , or the like. The detachable cross-members are preferably received in pockets  31  formed in the base beams  16  to ensure maximum rigidity of the apparatus  10 . The detachable cross-members  30  are removed when the apparatus  10  is to be positioned so that the wellhead  34  is flanked by the lifting devices  14 , as shown in FIG.  3 . The two pivot pins  22  should be lined up with a center of the wellhead  34  when the apparatus  10  is in the working position. The detachable cross-members  30  are re-connected to the base beams  16  after the apparatus is manoeuvred into the working position. A workover beam  36  is supported at each end by a cradle  40  that is fixed to an end of a ram  38  of the lifting device  14 . The workover beam  36  is preferably attached to the cradle  40  by lock pins  42  (FIG. 3) that are releasably received in bores in the workover beam  36  (the bores are not shown). A lifting sub  44  is releasably received in an aperture (not shown) in a middle of the workover beam  36 . The lifting sub  44  preferably incorporates a swivel  46  to permit the wellhead  34  and attached production tubing to be rotated while attached thereto. Alternately, the lifting sub  44  may be rotatably mounted to the workover beam  36  using ball bearings or the like. Extensions for the lifting sub  44  may be provided to accommodate connection to wellheads of varying height. 
     FIG. 5 illustrates a workover beam  48  which may be used in place of the workover beam  36  described above. A hydraulic motor  50  is mounted to the workover beam  48  and is operably connected to a lifting sub  52 . The hydraulic motor  50  is adapted to rotate the wellhead and attached tubing string to unseat or reseat packers or anchors, etc. when the lifting sub  52  is attached to the wellhead  34 . 
     The apparatus  10  may be constructed as a skid, as illustrated in FIG. 1, or it may be rubber wheel mounted and provided with a hitch for towing. The apparatus  10  is preferably not more than 8 feet (2.44 m) wide to enable legal highway towing and about 12 feet (3.66 m) long for extra base stability over the wellhead. The lifting devices  14  are preferably not less than 8 feet (2.44 m) long to ensure at least an 8 foot (2.44 m) stroke. The apparatus  60 , illustrated in FIG. 6, has a similar configuration to the apparatus  10 , except that a pair of wheel assemblies  62  are pivotally mounted to the base beams  16 , and a hitch member  64  that is mounted to the endmost permanent cross-member  28 . Alternatively, the hitch member  64  may be mounted to one or both of the removable cross-members  30 . Each wheel assembly  62  includes a wheel  66  which is rotatably supported by a pivot member  68 . The pivot member  68  is, in turn, pivotally mounted to an anchor member  70  which is welded to the outer side of the base beam  16 . A double-acting hydraulic cylinder  72  is pivotally mounted to the outside of the base beam  16  and a ram of the double-acting cylinder is pivotally connected to the pivot member  68  so that the wheel assembly  66  pivots down to support the apparatus  60  when the ram of the double-acting hydraulic cylinder  72  is stroked in. The pivot member is preferably locked in the lowered position shown in FIG. 6 using a locking pin (not shown), or the like. To place the apparatus  60  in the working position shown in FIG. 7, the locking pin (not shown) is removed from the pivot member  68  and the double-acting hydraulic cylinder  72  is operated so that the ram is extended and the wheel  66  pivots up off from the ground as illustrated in FIG.  7 . 
     FIG. 8 illustrates a hydraulic system used to augment the lifting device  14  when the lifting devices  14  are hydraulic cylinders. A pressure gauge  74  is connected to a hydraulic fluid supply line  76  which is connected to a pressurized hydraulic fluid source  78  and the lifting devices  14 . Readings taken from the pressure gauge  74  may be used to calculate the weight of the wellhead  34  and attached production tubing being lifted, using methods well known in the art. 
     In operation, the apparatus  10  is transported to a well site and is moved to a position in which the wellhead  34  is flanked by the base assemblies  12  and the two pivots  22  are aligned with the center of the wellhead  34 . The lifting devices  14  are pivoted from the horizontal position to the vertical position where they are stopped by the ram supports  20 . The lock pins  26  are inserted in the respective bores  24  to lock the cylinders  14  in the vertical position. The workover beam  36  is placed in the cradles  40  on the ram end of each lifting device  14 , and the lock pins  42  are inserted into the corresponding bores in the workover beam  36 . A lifting sub  44  and swivel  46  are assembled with a length that reaches a top of the wellhead  34 . Typically, a cap  35  on the wellhead  34  is removed after appropriate valves are closed and the lifting sub  44  is threadedly attached to a top of the wellhead  34 . The apparatus  10  is now ready to lift the wellhead  34 . The BOP  80  is closed and the wellhead  34  is unbolted at an appropriate flange depending on a specific workover or servicing to be done. 
     If the BOP is to be lifted, the well is killed first by injecting an appropriate fluid to overbalance natural pressure in the well. For example, in preparation for a well stimulation operation, a blowout preventer protector (BOP) disclosed by the Applicant in the U.S. Pat. No. 5,819,851 which issued on Oct. 13, 1998 is mounted to a top of the BOP  80 . Consequently, the well is killed and the wellhead is split below the tubing hanger. The wellhead  34  is lifted along with a production tubing  82  by the workover beam  36  as pressurized hydraulic fluid is injected into the lifting devices  14 . As will be understood by those skilled in the art, the wellhead  34  and the production tubing  82  may have to be rotated as they are lifted in order to unseat packers and/or anchors that support the production tubing  82  downhole. After the wellhead  34  is raised to a desired height, slips (not shown) are placed around the production tubing  82  to lock the production tubing  82  to the top of the flange of the tubing head spool  37  and then pressurized hydraulic fluid is released from the lifting devices  14 . The lifting sub  44  is removed from the wellhead  34  while the wellhead  34  is supported by a crane truck or the like. The wellhead  34  is then detached from the production tubing  82  and removed from the area. A BOP and a BOP protector (not shown) is placed on the top of the tubing head spool, a high pressure valve is mounted to the BOP protector and a blast joint is connected to a top of the production tubing string. 
     The workover beam  36  is replaced and the lifting sub  44  is connected to a top of the production tubing string  82 . High pressure hydraulic fluid is injected into the lifting devices  14  so that the slips can be removed. The production tubing string is then positioned and connected to a top of the high pressure valve in a manner well known in the art. Advantageously, a high pressure gauge (not shown) is connected to a top end of the production tubing string  82  to permit downhole pressure to be monitored during the well stimulation process. Thereafter, the kill fluid is blown out of the well and a fracturing or other stimulation operation can be conducted through the high-pressure valve and the BOP protector. After the stimulation treatment is completed, the process is reversed until the wellhead is repositioned on the well and the apparatus  10  is removed from the well site. 
     The apparatus  10  in accordance with the invention provides many distinct advantages over the prior art. For example, it is lightweight and can be quickly manoeuvred into position to service most wells. It requires only a few minutes of setup time and can be used to perform most workover and servicing jobs as long as there is no need to remove an extensive amount of production tubing from a well. It is also quickly removed from a well site. Furthermore, it requires fewer operators than a conventional rig, so operating overhead is reduced. 
     Changes and modifications to the above-described embodiment will no doubt be apparent to those skilled in the art. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.