Patent Publication Number: US-2018044872-A1

Title: Jackup drilling unit having material storage in jacking legs

Description:
BACKGROUND 
     This disclosure is related to the field of mobile offshore drilling units (MODUs). More specifically, the disclosure relates to jackup type MODUs which may be self-propelled and have storage capacity within the jacking legs to increase the available deck load of the drilling unit. 
     Jackup type MODUs (“jackups”) known in the art include a water-tight hull capable of flotation in a body of water. The hull may include wellbore drilling apparatus supported by the hull, fluid and supply storage in the hull, living quarters for personnel and power generation equipment. Jackups known in the art include three or more jacking legs movably coupled to the hull, typically through openings therefor through the hull proximate the perimeter of the hull. The jacking legs are most commonly truss-type structures, although cylindrical and other type structures are known for such purpose. The jacking legs may be longitudinally movably connected to the hull through various forms of a rack or similar gear-tooth structure, wherein the rack engages a jacking motor coupled to the hull. Rotation of the jacking motor causes the associated jacking leg to move downwardly to the water bottom and then to lift the hull out of the water to a selected distance above the mean water level (the “air gap”). Opposite rotation of the jacking motor causes the associated jacking leg to be lifted, such that the hull is lowered into the water (and thus be buoyantly supported) and the legs lifted from the water bottom to enable the hull to move along the water surface. 
     Jackups known in the art are typically barges, that is, they can move on the water surface only by being towed by one or more tow vessels. Jackups known in the art typically have the wellbore drilling apparatus disposed to one side of the hull. Earlier design jackups provided such arrangement by having the drilling apparatus positioned over a recessed feature formed in the perimeter of the hull. More recent design jackups have the drilling apparatus movable mounted to cantilever beams, whereby the drilling apparatus may be positioned substantially fully within the perimeter of the hull during movement of the jackup, and moved or “skidded” to a position outside the perimeter of the hull when the drilling apparatus is used to drill a wellbore below the water bottom. 
     A consideration in design and use of any particular jackup for any particular wellbore to be drilled is the “variable deck load” capacity of the hull. The variable deck load may include the weight of components and items that may be specific to a particular wellbore, for example, an amount of drilling fluid to be stored in tanks disposed in the hull, the total amount of drill pipe, drilling riser, drilling tools and well casing that must be carried on or in the hull in order to construct the wellbore and amounts of fuel, lubricants and other fluids, e.g., potable water, that must be carried by the hull to support drilling operations. To the extent that such components and other items may be supported other than by the hull, it may be possible to increase the effective drilling capacity of a particular jackup by enabling more drill pipe, drilling tools, drilling riser and casing to be supported by the hull. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side elevation view of an example jackup drilling unit according to the present disclosure. 
         FIG. 2  shows an example embodiment of a jacking leg according to the present disclosure. 
         FIG. 3  shows an example embodiment of a leg jacking system having an internal storage tank. 
         FIG. 4  shows an automatic control system for maintaining a selected elevation of a storage tank inside a jacking leg. 
     
    
    
     DETAILED DESCRIPTION 
     An example mobile offshore drilling unit is shown in  FIG. 1  at  10 . The drilling unit  10  in the present example is called a “jackup” drilling unit, as explained in the Background section herein. Such drilling units are supported at the water bottom  20  by jacking legs  12  that can be moved along their longitudinal direction with respect to a hull  14 C of the drilling unit  10  by operating jacking motors  12 B. the jacking legs  12  in the embodiment shown in  FIG. 1  may be cylindrically shaped. 
     The jacking motors  12 B may each turn a respective gear unit (not shown) the output of which is in contact with a rack  12 A or similar linear gear-toothed structure disposed on the jacking leg  12  and extending along a substantial portion of its length. Other types of jackup drilling rigs may use a pinhole/hydraulic jacking system to move the legs, for example. An example of such jacking system will be further explained with reference to  FIG. 3 . The jacking legs  12  may include a “spud can”  12 C at a bottom end thereof for contacting the water bottom  20  and supporting the weight of the drilling unit  10 . During set up of the drilling unit  10  on a well location, the hull  14 C floats and may be moved to the selected location by tug boats or similar towing vessels as the legs  12  are maintained substantially in their uppermost position with respect to the hull  14 C. The jacking legs  12  are positioned within and move within corresponding openings  14 D in the hull  14 C. Such openings  14 D provide a path through the hull  14 C for the jacking legs  12 , but are sealed on their interior surface so that water is excluded from entering the interior of the hull  14 C. 
     When the unit  10  is positioned at the selected location, the hull  14  is positioned both geodetically and with the hull  14 C in a preferred geodetic orientation. The jacking legs  12  are moved longitudinally (called “jacking”) using the jacking motors  12 B (or hydraulic motors in hydraulically jacked leg examples as shown in  FIG. 3 ). Downward movement of the jacking legs  12  with respect to the hull  14 C eventually causes the spud cans  12 C to contact the water bottom  20 . When the spud cans  12 C contact the water bottom  20 , continued movement of the jacking legs  12  with respect to the hull  14 C causes the hull  14 C to move upwardly out of the water. The jacking continues until the hull  14 C is positioned at a selected height (“air gap”)  22  above the mean water surface  18 . 
     When the selected air gap  22  is obtained, a cantilever structure (“cantilever”)  14  may be laterally displaced from its transport position generally over the hull  14 C. Such lateral displacement, called “skidding out” the cantilever  14 , may be performed by a cantilever skid motor  14 B that rotates a gear (not shown) in contact with a cantilever skid rack  14 A. Other examples of a cantilever may use a pinhole/hydraulic skidding unit in contact with the cantilever skid rack  14 A. The skid out continues until a drilling rig  29 , supported generally near the outward end of the cantilever  14 , is positioned over a proposed well location  31  on the water bottom  20 . The drilling rig  29  may include pipe lifting, supporting and rotating devices familiar to those skilled in the art, for example, a derrick  24  in which is included a tubular or pipe rack  32  to vertically support assembled “stands” of tubulars  34  used in wellbore drilling, testing and completion operations. The drilling rig  29  may include a winch called a drawworks  26  that spools and unspools wire rope or cable, called “drill line”  27 , for raising and lowering a traveling block and hook  28 . The hook  28  may support a top drive  30  or similar device for applying rotational energy to the pipe for various drilling and well completion operations. 
     In the present example, sensors may be associated with some of the foregoing drilling unit components to measure one or more parameters used in some types of data recording systems. The parameters measured by the various sensors described herein may be characterized as being related to the beginning and the end of one or more “auxiliary operations.” As used in the present description, the term “auxiliary operations” is intended to mean any function or operation on the drilling unit  10  that is not related to equipment or devices being inserted into or removed from a wellbore (including the active drilling of such wellbore), but is nonetheless essential to enabling the drilling unit  10  to perform intended drilling operations. The above examples of jacking the legs  12  until the selected air gap  22  is obtained, as well as skidding the cantilever  14  are two of such auxiliary operations. 
     As an example, each jacking motor  12 B may include a sensor and an associated wireless data transceiver (shown at  11  collectively) for measuring electric current drawn by the respective jacking motor  12 B. A similar wireless transceiver/sensor combination  11  may be associated with the cantilever skid motor  14 B. A transponder, such as an acoustic or laser range finder, or a global positioning system receiver, shown at  36 , may be disposed proximate a bottom surface of the hull  14 C in order to measure the air gap  22 . Such sensor  36  may also include an associated wireless transceiver  11 . A data acquisition system (“DAQ”)  33  may be disposed at a convenient position on the drilling unit  10  and include a wireless transceiver  11 A for receiving data from the various sensors, such as those described above. Although in the present example the various sensors include wireless transceivers  11  to communicate with the DAQ  33 , it should be clearly understood that “wired” sensors may also be used in accordance with the invention. 
     The drilling rig  29  may also include sensors for measuring various parameters related to operation of the drilling rig  29 . An example of such sensors and methods for validating and interpreting the measurements made by the rig sensors to automatically determine what drilling operation is underway at any time are described in U.S. Pat. No. 6,892,812 issued to Niedermayr et al. and incorporated herein by reference. As shown in  FIG. 1 , one such sensor is can be a load cell  27 A arranged to determine the total axial force (weight) supported by the drilling unit  29 . The load cell  27 A may be coupled wirelessly through a transceiver  11  to the DAQ  33 . Such load cell is generally known in the art as a “weight indicator.” Another sensor may be a pressure/volume sensor  126  associated with pumps (not shown) configured to move fluid through appropriate rotary seals in the top drive  30  and into any pipe coupled to the top drive, such as a drill string or casing. The pressure/volume sensor  126  may include a pressure transducer (not shown separately) and a device known in the art as a “stroke counter” or similar device that measures a parameter related to the volume displacement of pistons within cylinders in a “mud pump.” The pressure volume sensor  126  may also be wirelessly coupled to the DAQ  33 . The weight indicator (load cell  27 A) and the pressure/volume sensor  126  may be used to make measurements related to the start and stop times of various operations. The foregoing sensors may be used in some examples to identify and record start and stop times of auxiliary operations as more fully set forth in U.S. Pat. No. 7,886,845 issued to King et al. It should be understood that the foregoing sensors and DAQ  33  in the present example are not intended to limit the scope of the present invention but are described only to illustrate one example embodiment of a jackup drilling unit. In the present example embodiment, an elevation sensor  124  may be affixed proximate the top of one or more of the jacking legs  12  to communicate a signal to the DAQ  33  indicative of the jacking position with respect to the hull  14 C of the associated jacking leg  12 . Use of the measurements from such sensor  124  will be further explained with reference to  FIGS. 2 and 4 . The elevation sensor  124  may be an acoustic sensor, a capacitance proximity sensor, magnetic proximity sensor or any other sensor that enables determination of the longitudinal position of the jacking leg  12  with respect to the hull  14 C. 
       FIG. 2  shows an example of one of the jacking legs  12  according to the present disclosure in more detail. The jacking leg  12  may be formed substantially as a hollow cylinder. The previously described spud can  12 A may be disposed at the bottom of the jacking leg  12 . A storage tank  25  may be disposed in the interior of the jacking leg  12 . The interior of the jacking leg  12  and the exterior surface of the storage tank  25  may be suitably shaped to enable the storage tank  25  to move longitudinally within the interior of the jacking leg  12 . One or more cable sheaves  17 B may be affixed to a top end of the storage tank  25 . A like number of cable sheaves  17 B may be affixed proximate an upper end of the jacking leg  12 . A cable  17 , for example, made from wire rope or the like, may extend from a winch  21  affixed in a suitable location on the hull  14 , through a first sheave  17 A, through the one or more sheaves  17 B both at the upper end of the jacking leg  12  and on the top of the storage tank  25 , to a fixed end which may be on the storage tank  25 , the hull  14 C or the jacking leg  12 . The winch  21  may include a sensor  21 A such as a rotary encoder or other sensor for measuring rotation of the winch, and consequently, an amount of the cable  17  that is extended from the winch at any time. Signals from the sensor  21 A may be used to determine the elevation of the storage tank  25  inside the jacking leg. 
     One or more fluid transfer hoses  19  may be stored on a constant tension reel  23 , and may extend to the top end of the jacking leg over a hose sheave  19 A configured for the number of fluid transfer hoses used in any particular embodiment. The one or more fluid transfer hoses  19  are in fluid communication with the interior of the storage tank  25 . Fluid may be moved into and out of the storage tank  25  by any known method, for example, air or inert gas pressure displacement, or buoyant liquid displacement. 
     In the present example embodiment, operation of the winch  21  may be synchronized with longitudinal movement of the jacking leg  12  so that the storage tank  25  is maintained at a same elevation with respect to the hull  14 C as the jacking leg  12  is moved from its fully raised position as shown in the figures to its fully lowered position. In the present example embodiment, the storage tank  25  may be maintained at an elevation such that it is entirely disposed between the uppermost deck surface of the hull  14 C, i.e., entirely within the jacking leg opening ( 14 D in  FIG. 1 ), and entirely above the water surface  18 . As will be appreciated by those skilled in the art, by maintaining the elevation of the storage tank  25  above the water surface  18  at all times, the storage tank may store water-immiscible and/or hazardous fluids such as engine fuel without the need to provide the storage tank  25  with a double walled construction. Further, because the weight of the storage tank  25  is transferred to the jacking leg  12  through the cable  17 , the hull  14 C does not support any part of the weight of the storage tank  25 . Thus, the weight of the storage tank  25  may be made available as part of the available variable deck load of the jackup drilling unit ( 10  in  FIG. 1 ). Further, because the storage tank  25  may be maintained at an elevation inside the jacking leg  12  substantially always within the jacking leg opening ( 14 D in  FIG. 1 ) in the hull  14 C, the portion of the jacking leg  16  in which the storage tank  25  is suspended may be further protected from damage by collision with objects in the water. 
     In other embodiments, the storage tank  25  may be moved to any other selected elevation with respect to the hull  14 C or maintained at any other selected elevation with respect to the water surface  18 . 
     In some embodiments, a storage tank and winch structure as shown in  FIG. 4  may be included in any or all of the jacking legs in a jackup mobile offshore drilling unit according to the present disclosure. 
       FIG. 3  shows an example jacking apparatus  12 D that may be disposed a jacking house in each jacking leg opening ( 14 D in  FIG. 1 ). The jacking apparatus may be of a type commercially available from GustoMSC B. V., Karel Doormanweg 25, 3115 J D Schiedam, The Netherlands. Such jacking apparatus may be configured for continuous jacking leg movement during jacking operations. The jacking apparatus  12 D may include a frame  118  onto which are mounted a plurality of double acting hydraulic cylinders  120 . A pair of the hydraulic cylinders  120  moves each of a plurality of jacking pins  122  longitudinally with respect to the frame  118 . The jacking pins  122  may be selectively inserted into and withdrawn from openings  116  in the exterior of the jacking leg  12  to enable the movement of the hydraulic cylinders  120  to effect longitudinally continuous movement of the jacking leg  12  up or down depending on the operation of the hydraulic cylinders  120  and jacking pins  122 . 
       FIG. 4  shows an example embodiment of a jacking controller that may be used in some embodiments to synchronize operation of the winch ( 21  in  FIG. 2 ) with operating of the jacking apparatus  12 D so that the storage tank ( 25  in  FIG. 2 ) is maintained a substantially constant, selected elevation. Signals from the sensor  21 A on the winch ( 21  in  FIG. 2 ) may be communicated to a controller  100 . The controller  100  may be any type of automated process controller, including, without limitation a microprocessor with suitable power device drivers, a programmable logic controller, a field programmable gate array and an application specific integrated circuit. The controller  100  may in some embodiments form part of or be in signal communication with the DAQ ( 33  in  FIG. 1 ) Signals from the jacking leg elevation sensor  124  may also be in signal communication with the controller  100 . Control signals generated by the controller  100  may be used to operate the jacking apparatus, shown schematically at  16 C, and the winch  21  to maintain the elevation of the storage tank ( 25  in  FIG. 2 ) as the jacking leg ( 12  in  FIG. 1 ) is raised or lowered. 
     While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.