CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of co-pending U.S. Provisional Application Serial No. 61/791,258, filed March 15 ^th , 2013, the full disclosure of which is hereby incorporated by reference herein for all purposes.

BACKGROUND OF THE INVENTION

Field of Invention

[0002] The present disclosure relates in general to a system and method for maintaining volume in a bladder pump at the end of each pump stroke.

Description of Prior Art

[0003] Subsea drilling systems typically employ a vessel at the sea surface, a riser connecting the vessel with a wellhead housing on the seafloor, and a drill string. A drill bit is attached on a lower end of the drill string, and used for excavating a borehole through the formation below the seafloor. The drill string is suspended subsea from the vessel into the riser, and is protected from seawater while inside of the riser. Past the lower end of the riser, the drill string inserts through the wellhead housing just above where it contacts the formation. Generally, a rotary table or top drive is provided on the vessel for rotating the string and bit. Drilling mud is usually pumped under pressure into the drill string, and is discharged from nozzles in the drill bit. The drilling mud, through its density and pressure, controls pressure in the well and cools the bit. The mud also removes formation cuttings from the well as it is circulated back to the vessel. Traditionally, the mud exiting the well is routed through an annulus between the drill string and riser. However, as well control depends at least in part on the column of fluid in the riser, the effects of corrective action in response to a well kick or other anomaly can be delayed.

[0004] Fluid lift systems have been deployed subsea for pressurizing the drilling mud exiting the wellbore. Piping systems outside of the riser carry the mud pressurized by the subsea lift systems. The lift systems include pumps disposed proximate the wellhead, which reduce the time for well control actions to take effect.

SUMMARY OF THE INVENTION

[0005] A method and system for lifting drilling mud from subsea to a drilling vessel. Drilling mud exiting a wellbore is directed to a subsea pump that includes a body, a chamber in the body, and a bladder in the chamber. An outer periphery of the bladder sealingly attaches to the body, and defines a water side and a mud side in the chamber. A mud inlet valve selectively opens to allow mud to flow into the mud side of the chamber. As mud enters the chamber, the bladder is moved into the water side, and urges water in the water side from the chamber and through a selectively opened water exit valve. Pressurized water enters the chamber through a selectively opened water inlet valve, which in turn exerts a force against the bladder that urges the mud from the chamber through a selectively opened mud exit valve. The bladder maintains a barrier between the mud and water as it reciprocates in the chamber. The travel of the bladder in the chamber is controlled to prevent damage from contact with the chamber.

BRIEF DESCRIPTION OF DRAWINGS

[0006] Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: [0007] FIG. 1 is a side sectional view of an example of a subsea drilling system in accordance with the present invention.

[0008] FIGS. 2 and 3 are partial side sectional views of an example of a subsea pump for use with the drilling system of FIG. 1 in different pumping modes and in accordance with the present invention.

[0009] FIG. 4 is a side view of an embodiment of a subsea drilling system with a riser and pump kit, and in accordance with an embodiment of the invention.

[0010] While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF INVENTION

[0011] The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout.

[0012] It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation.

[0013] Shown in Figure 1 is a side partial sectional view of an example embodiment of a drilling system 10 for forming a wellbore 12 subsea. The wellbore 12 intersects a formation 14 that lies beneath the sea floor 16. The wellbore 12 is formed by a rotating bit 18 coupled on an end of a drill string 20 shown extending subsea from a vessel 22 floating on the sea surface 24. The drill string 20 is isolated from seawater by an annular riser 26; whose upper end connects to the vessel 22 and lower end attaches onto a blowout preventer (BOP) 28. The BOP 28 mounts onto a wellhead housing 30 that is set into the sea floor 16 over the wellbore 12. A mud return line 32 is shown having an end connected to the riser 26 above BOP 28, which routes drilling mud exiting the wellbore 12 to a lift pump assembly 34 schematically illustrated subsea. Within the lift pump assembly 34, drilling mud is pressurized for delivery back to the vessel 22 via mud return line 36.

[0014] Figure 2 includes a side sectional view of an example of a pump 38 for use with lift pump assembly 34 (Figure 1). Pump 38 includes a generally hollow and elliptically shaped pump housing 40. Other shapes for the housing 40 include circular and rectangular, to name a few. An embodiment of a flexible bladder 42 is shown within the housing 40; which partitions the space within the housing 40 to define a mud space 44 on one side of the bladder 42, and a water space 46 on an opposing side of bladder 42. As will be described in more detail below, bladder 42 provides a sealing barrier between mud space 44 and water space 46. In the example of Figure 2, bladder 42 has a generally elliptical shape and an upper open space 48 formed through a side wall. Upper open space 48 is shown coaxially registered with an opening 50 formed through a side wall of pump housing 40. A disk-like cap 52 bolts onto opening 50, where cap 52 has an axially downward depending lip 53 that coaxially inserts within opening 50 and upper open space 48. A portion of the bladder 42 adjacent its upper open space 48 is wedged between lip 53 and opening 50 to form a sealing surface between bladder 42 and pump housing 40.

[0015] A lower open space 54 is formed on a lower end of bladder 42 distal from upper open space 48, which in the example of Figure 2 is coaxial with upper open space 48. An elliptical bumper 56 is shown coaxially set in the lower open space 54. The bumper 56 includes upper and lower segments 58, 60 coupled together in a clamshell like arrangement, and that respectively seal against upper and lower radial surfaces on the lower open space 54. The combination of sealing engagement of cap 52 and bumper 56 with upper and lower open spaces 42, 54 of bladder 42, effectively define a flow barrier across the opposing surfaces of bladder 42. Further shown in the example of Figure 2 is an axial rod 62 that attaches coaxially to upper segment 56 and extends axially away from lower segment 58 and through opening 50.

[0016] Still referring to Figure 2, a mud line 64 is shown having an inlet end connected to mud return line 32, and an exit end connected with mud return line 36. A mud inlet valve 66 in mud line 64 provides selective fluid communication from mud return line 32 to a mud lead line 68 shown branching from mud line 64. Lead line 68 attaches to an annular connector 70, which in the illustrated example is bolted onto housing 40. Connector 70 mounts coaxially over an opening 72 shown formed through a sidewall of housing 40 and allows communication between mud space 44 and mud line 64 through lead line 68. A mud exit valve 74 is shown in mud line 64 and provides selective communication between mud line 64 and mud return line 36. [0017] Water may be selectively delivered into water space 46 via a water supply line 76 (Figure 1) shown depending from vessel 22 and connecting to lift pump assembly 34. Referring back to Figure 2, a water inlet lead line 78 has an end coupled with water supply line 76 and an opposing end attached with a manifold assembly 80 that mounts onto cap 52. The embodiment of the manifold assembly 80 of Figure 2 includes a connector 82, mounted onto a free end of a tubular manifold inlet 84, an annular body 86, and a tubular manifold outlet 88, where the inlet and outlet 84, 88 mount on opposing lateral sides of the body 86 and are in fluid communication with body 86. Connector 82 provides a connection point for an end of water inlet lead line 78 to manifold inlet 84 so that lead line 78 is in communication with body 86. A lower end of manifold body 86 couples onto cap 52; the annulus of the manifold body 86 is in fluid communication with water space 46 through a hole in the cap 52 that registers with opening 50. An outlet connector 90 is provided on an end of manifold outlet 88 distal from manifold body 86, which has an end opposite its connection to manifold outlet 88 that is attached to a water outlet lead line 92. On an end opposite from connector 90, water outlet lead line 92 attaches to a water discharge line 94; that as shown in Figure 1, may optionally provide a flow path directly subsea.

[0018] A water inlet valve 96 shown in water inlet lead line 78 provides selective water communication from vessel 22 (Figure 1) to water space 46 via water inlet lead line 78 and manifold assembly 80. A water outlet valve 98 shown in water outlet lead line 92 selectively provides communication between water space 46 and water discharge line 94 through manifold assembly 80 and water outlet lead line 92.

[0019] In one example of operation of pump 38 of Figure 2, mud inlet valve 66 is in an open configuration, so that mud in mud return line 32 communicates into mud line 64 and mud lead line 68 as indicated by arrow A _M I. Further in this example, mud exit valve 74 is in a closed position thereby diverting mud flow into connector 70, through opening 72, and into mud space 44. As illustrated by arrow Au, bladder 42 is urged in a direction away from opening 72 by the influx of mud, thereby imparting a force against water within water space 46. In the example, water outlet valve 98 is in an open position, so that water forced from water space 46 by bladder 42 can flow through manifold body 86 and manifold outlet 88 as illustrated by arrow Α _% ¾· After exiting manifold outlet 88, water is routed through water outlet lead line 92 and into water discharge line 94.

[0020] An example of pressurizing mud within mud space 44 is illustrated in Figure 3, wherein valves 66, 98 are in a closed position and valves 96, 74 are in an open position. In this example, pressurized water from water supply line 76 is free to enter manifold assembly 80 where as illustrated by arrow A _W i, the water is diverted through opening 50 and into water space 46. Introducing pressurized water into water space 46 urges bladder 42 in a direction shown by arrow A _D . Pressurized water in the water space 46 urges bladder 42 against the mud, which pressurizes mud in mud space 44 and directs it through opening 72. After exiting opening 72, the pressurized mud flows into lead 68, where it is diverted to mud return line 36 through open mud exit valve 74 as illustrated by arrow A _Mo . Thus, providing water at a designated pressure into water supply line 76 can sufficiently pressurize mud within mud return line 36 to force mud to flow back to vessel 22 (Figure 1).

[0021] As illustrated in Figures 2 and 3, bumper 56 travels axially within housing 40, and has end strokes proximate to the inner surface of housing 40. An optional controller 100 (Figure 1) may be provided for limiting travel of bladder 42 and bumper 56 to avoid collisions of bladder 42 or bumper 56 with the inner surface of housing 40. In an embodiment, controller 100 includes an information handling system, and receives or contains instructions to selectively operate valves 66, 74, 78, 98. Optionally, valves 66, 74, 78, 98 can include actuators (not shown) in communication with and/or controlled by controller 100, that manipulate the valves 66, 74, 78, 98 to limit travel of the bumper 56. The controller 100 can be set based upon an increase or decrease in fill volume that alters velocity of flow in one of the chambers 44, 46. User defined set points can be input to the controller 100 for establishing limits of travel of the bladder 42. This can be manifested via control of the valves 66, 74, 96, 98 so that they open and close at designated times and sequences so that travel of bladder 42 and/or bumper 56 prevents or avoids collision with housing 40. Moreover, a set bias may be included with commands in the controller so that the control system automatically adjusts the set points to a higher or lower value to bring bladder travel within a safe range and thereby avoid any damaging contact. Examples exist wherein volume in one of the chambers 44, 46 at a maximum stroke ranges from about 15 gallons to about 55 gallons. By setting the set points with an included bias, the set points are adjusted during use so that in a subsequent cycle of pumping, the extent of bladder travel is decreased to avoid any overshoot from a designated position.

[0022] Referring now to Figure 4, an alternate embodiment of drilling system 10A is shown in side partial sectional view and wherein lift pump assembly 34A includes a mud pump kit 102 mounted integral onto riser 26A. In this example, mud pump kit 102 includes a subsea module 104 shown circumscribing riser 26A and that includes mud distribution manifold (not shown) and other flow control devices for selectively diverting flow to desired destinations. A riser module 106 is illustrated mounted on an upper surface of subsea module 104, which also circumscribes riser 26A. Riser module 106 of Figure 4 includes hydraulic power units for pressurizing hydraulic fluid that in an example is used for actuating devices subsea. Riser module 106 also includes hydraulic control systems connection hardware for mounting mud pump kit 102 to riser 26A. Pumps 38 (Figure 2) are housed in pump modules 108, 110 shown set on riser module 106. In an embodiment, pump modules 108, 110 each include three pumps 38. A solids recovery unit (SRU) 112 is shown above the pump modules 108, 110, and a subsea rotating device (SRD) 114 attaches to an upper end of SRU 112. An upper end of SRD 114 flangedly attaches to a riser joint 116, where in one example a substantial portion of the riser 26 A between SRD 114 and vessel 22 (Figure 1) is made up of stacked riser joints 116.

[0023] In the example of Figure 4, mud exiting drill string 20 flows upward in an annulus 118 defined between drill string 20 and wellbore 12, and which extends further upward between drill string 20 and riser 26 A. The mud flows past mud pump kit 102 and SRU 112 within annulus 118 and into SRD 114 where a packer (not shown) blocks the mud. In an embodiment, the annulus 118 above packer is filled with sea water or other fluid. Mud within annulus 118 below packer is diverted to SRU 112 where cuttings or other solids are removed or particulated. After being processed in the SRU 112, the mud is directed to the pump modules 108, 110 where it is pressurized so it can flow back to vessel 22. Processing the mud in the SRU 112 can prevent damage to the pumps 38 (Figure 2) in the modules 108, 110.

[0024] In an example, modules 104, 106, 108, 110 are modular elements that can be transported separately to the vessel 22 (Figure 1) on site, where the pump kit 102 is assembled. A significant time savings is one advantage of the modularity of modules 104, 106, 108, 110. Because loading a fully assembled pump kit 102 onto a vessel 102 causes such an asymmetric weight distribution that requires anchoring and stabilization, which is unachievable on site. Whereas the vessel 22 can accommodate individual modules 104, 106, 108, 110 on site and without becoming unstable. Pump modules 108, 110 are individually detachable from the pump kit 102, and thus further enhancing modularity of the pumping system. Dedicated piping (not shown) is routed from SRU 112 and separately to each module 108, 110 so that one of the modules 108, 110 can remain operational while the other is removed or otherwise out of service. Further, spare modules can be kept on site for one or both modules 108, 110, and can installed in place of a one of the modules 108, 110 with little or no stoppage of operation of pumping mud to the vessel 22.

[0025] In an alternate embodiment, BOP 28A is a BOP stack, whose upper portion includes an annular blowout preventer and is part of a lower marine riser package (LMRP). Addtionally, LMRP can include controls, a multiplexer unit, and pods. In an embodiment, modules 104, 106, 108, 110, SRU 112, SRD 114, BOP 28A, and riser joints 116 are delivered to the vessel 22 (Figure 1) while on site and disposed above wellbore 12. While on the vessel 22, modules 104, 106, 108, 110 are attached together to form mud pump kit 102 which is coupled with BOP 28A. SRU 112 and SRD 114 are attached onto mud pump kit 102; while suspended from riser joints 116 the assembled unit is lowered subsea onto wellhead housing 30.

[0026] The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.