Abstract:
Systems and methods contain fluids discharged from a subsea well or at the surface by capping the well blowout with a pre-positioned capping device. The capping device includes at least one blind shear ram and is separate from a blowout preventer. The blowout preventer may operate to control well events up to a certain pressure, above which the capping device is employed since the capping device has a higher pressure rating than the blowout preventer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a non-provisional application which claims benefit under 35 USC §119(e) of and priority to U.S. Provisional Application Ser. No. 61/847,895 filed 18 Jul. 2013, entitled “PRE-POSITIONED CAPPING DEVICE FOR SOURCE CONTROL WITH INDEPENDENT MANAGEMENT SYSTEM,” which is incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    Embodiments of the invention relate generally to systems and methods for containing fluids discharged from a subsea well or at the surface. 
       BACKGROUND OF THE INVENTION 
       [0003]    In offshore floating drilling operations, a blowout preventer (BOP) can be installed on a wellhead at the sea floor and a lower marine riser package (LMRP) mounted to the BOP. In addition, a drilling riser extends from a flex joint at the upper end of LMRP to a drilling vessel or rig at the sea surface. A drill string is then suspended from the rig through the drilling riser, LMRP, and the BOP into the wellbore. A choke line and a kill line also suspend from the rig and couple to the BOP, usually as part of the drilling riser assembly. 
         [0004]    Another type of offshore drilling unit is a jack-up unit, which may include a BOP at the surface located on the unit. The jack-up unit can drill with a subsea wellhead on the seabed, a high pressure riser up to the jack-up unit, and the surface BOP connected to the high pressure riser. Offshore drilling can also be done from an offshore platform, a piled structure, a gravity based structure, or other permanent type structure. These drilling operations may use a surface BOP. 
         [0005]    During drilling operations, drilling fluid, or mud, is delivered through the drill string and returned up an annulus between the drill string and casing that lines the well bore. In the event of a rapid influx of formation fluid into the annulus, commonly known as a “kick,” the BOP may be actuated to seal the annulus and control the well. In particular, BOP&#39;s include closure members capable of sealing and closing the well in order to prevent release of high-pressure gas or liquids from the well. Thus, the BOP&#39;s are used as safety devices to close, isolate, and seal the wellbore. Heavier drilling mud may be delivered through the drill string, forcing fluid from the annulus through the choke line or kill line to protect the well equipment disposed above the BOP from the high pressures associated with the formation fluid. Assuming the structural integrity of the well has not been compromised, drilling operations may resume. However, if drilling operations cannot be resumed, cement or heavier drilling mud is delivered into the well bore to kill the well. 
         [0006]    In the event the BOP fails to actuate, or insufficiently actuates, in response to a surge of formation fluid pressure in the annulus, a blowout may occur. Containing and capping the blowout may present challenges since the wellhead may be hundreds or thousands of feet below the sea surface and, with surface BOP&#39;s, the flow presents a great danger of fire or explosion. Personnel are forced to evacuate the drilling unit if a well blows out as it is very dangerous. 
         [0007]    Accordingly, there remains a need in the art for systems and methods to cap a well quickly to stop flow. Such systems and methods would be particularly well-received if they offered the potential to cap a well discharging hydrocarbon fluids almost immediately. This would reduce potential environmental damage and danger to personnel and the drilling unit. 
         [0008]    Well capping subsea is an involved process. The floating drilling unit may have been damaged, even sunk, on location. Debris from the drilling unit has to be cleared from the wellsite. Preparations involve injecting dispersants subsea into the blowout to disperse oil and gas in the water column. This dispersion then allows vessels with debris removal equipment to clear the area around the BOP. Once this area is cleared, another vessel can install the capping stack and shut in the well. This process can take 10 to 21 days with uncontrolled well flow to the environment. Complexness of this operation may require five or more large vessels. 
         [0009]    Well capping with a surface BOP offshore, jack-up or platform takes a similar time period. During the capping operation the danger of fire and explosion is always present. If fire or explosion does occur, the platform or jack-up can be a complete loss. If the platform has multiple wells, all the wells can blowout. To ensure fire or explosion does not occur, the drilling unit must be deluged with water from several vessels at a high rate. Once deemed safe, personnel inspect the surface BOP and determine how the well can be capped. Debris is cleared by personnel, and BOP equipment is examined. During this period, the deluge from vessels continues and the well flows to the environment. A plan is determined, and the well is capped. 
       SUMMARY OF THE INVENTION 
       [0010]    In an embodiment, a staged pressure control system attached to a wellhead of a well includes a blowout preventer stack having a first pressure rating. A pre-positioned capping device includes a blind shear ram disposed between the wellhead and the blowout preventer stack to close the well. A second pressure rating of the capping device exceeds the first pressure rating of the blowout preventer stack. 
         [0011]    For another embodiment, a method of controlling a well includes disposing a pre-positioned capping device between a wellhead of the well and a blowout preventer stack having a first pressure rating. The method further includes drilling the well through the capping device and blowout preventer stack and operating the blowout preventer stack to control well events up to a pressure limit. In addition, the method includes controlling a blind shear ram of the pre-positioned capping device having a second pressure rating higher than the first pressure rating in order to close the well if the well event is greater than the pressure limit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The invention, together with further advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which: 
           [0013]      FIG. 1  is a schematic diagram illustrating a jack-up drilling rig unit in accordance with an embodiment of the present invention. 
           [0014]      FIG. 2  is a schematic diagram illustrating a pre-positioned capping device attached to a wellhead in accordance with an embodiment of the present invention. 
           [0015]      FIG. 3  is a schematic diagram illustrating control of the pre-positioned capping device in accordance with an embodiment of the present invention. 
           [0016]      FIG. 4  is a schematic diagram illustrating use of a pre-positioned capping device with a blowout preventer stack having a lower pressure rating than the capping device in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Reference will now be made in detail to embodiments of the present invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the invention, not as a limitation of the invention. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used in another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations that come within the scope of the appended claims and their equivalents. 
         [0018]    By way of explanation and not by way of limitation, the following description focuses on subsea pre-positioned capping device (PCD) used with a jack-up drilling unit. However, it is to be clearly understood that the principles of the present invention are not limited to environments as described herein. Thus, the use of the PCD on a jack-up drilling unit is described herein as merely an example of the wide variety of uses for the principles of the present invention. The PCD can be used with a subsea BOP or any surface BOP with location being subsea, on a lower level below the BOP, or positioned immediately below the BOP. 
         [0019]      FIG. 1  illustrates a jack-up drilling rig unit  10  depicted with a jack-up rig  100  resting on the sea-bed  20 . The jack-up rig  100  is a type of mobile platform including a buoyant hull  160  fitted with a number of movable legs  140 , capable of raising the hull  160  over the surface of the sea. The buoyant hull  160  enables transportation of the unit  10  and all attached machinery to a desired location. Once on location, the hull  160  raises to the required elevation above the sea-bed  20  surface on its legs  140  supported by the sea-bed  20 . 
         [0020]    The legs  140  of such units may be designed to penetrate the sea-bed  20 , may be fitted with enlarged sections or footings, or may be attached to a bottom mat. Footings or spudcans  180  spread the load so the rig  100  does not sink into the sea-bed  20 . The base of each leg  140  is fitted with a spudcan  180 , which may include a plate or dish designed to spread the load and prevent over penetration of the leg  140  into the sea-bed  20 . The spudcans  180  may be circular, square or polygonal. 
         [0021]    A high pressure riser  220  leads to the wellhead  200  in the sea-bed  20 . The high pressure riser  220  may be a thick walled, high strength riser and can contain full well pressure. A surface blowout preventer (BOP) stack  240  is located on the jack-up rig  100 . The PCD  300  is pre-installed on the wellhead  200 . 
         [0022]    The PCD  300  functions as an independent safety and containment device for well leakage and/or blowout. The PCD  300  is installed on the well when the BOP stack  240  is installed and is a safety device to be used if the drilling unit&#39;s BOP stack  240  fails to control a well blowout. When necessary, the PCD  300  is activated immediately to regain control of the well leak or blowout providing a secondary level of environmental and personnel protection. The PCD  300  can additionally function to secure the well by closure of the PCD  300  if the rig must be moved. 
         [0023]      FIG. 2  shows the PCD  300  designed for attachment onto substantially any wellbore worldwide and for functioning in subsea and surface operations. The PCD  300  forms a capping stack, which may include a first blind shear ram  301 , a second blind shear ram  302 , a power source  307  for closing the rams  301 ,  302  and that is independent from the rig  100  and an independent control system  303 . The power source  307  (e.g., pressurized tanks with hydraulic fluid) of the PCD  300  provides stored power to the control system  303  and as otherwise necessary for actuation of the PCD  300  without relying on power from the rig  100 . Since the power source  307  may form an integral component of the PCD  300  and be disposed remote from the rig  100 , collocation of the power source  307  with the blind shear rams  301 ,  302  enables operability without relying on hydraulic pressure supplied from the rig  100 . 
         [0024]    The blind shear rams  301 ,  302  (also known as shear seal rams, or sealing shear rams) seal the wellbore, even when the bore is occupied by a drill string, by cutting through the drill string as the rams  301 ,  302  close off the well. The upper portion of the severed drill string is freed from the ram  301 ,  302 , while the lower portion may be crimped and the “fish tail” captured to hang the drill string. For some embodiments, the independent control system  303  for the PCD  300  may not actuate the rams  301 ,  302  during normal drilling or kick occurrences handled by the BOP stack  240  but rather only upon the independent control system  303  being operated for loss of control for which the BOP stack  240  does not or cannot regain control. 
         [0025]    The PCD  300  may further include at least one pressure and/or temperature transducer below each ram  301 ,  302  capable of analogue local display. The PCD  300  may have a number of outlets  304 . Each outlet may be provided with two hydraulically controlled gate valves. Two of the outlets may be equipped with manually controlled chokes to perform soft shut-in of the second blind shear ram  302 . The capping stack may also include an inlet  305  to inject glycol or methanol to mitigate hydrate formation. 
         [0026]    As described in further detail with respect to  FIG. 3 , the independent control system  303  activates the PCD  300  independent from activation of the BOP stack  240  and can be operated by the drilling rig unit  10  or from a vessel or other installation remote from the drilling rig unit  10 . For some embodiments, the control system  303  includes a self-contained electrical supply, such as a battery, for any functions of the control system  303  described herein and utilizing current independent of the drilling rig unit  10 . In some embodiments, the independent control system  303  may form part of a digital acoustic control system. The digital acoustic control system may utilize low frequency sound sent to, or received from, the control system  303  on the PCD  300 . 
         [0027]      FIG. 3  depicts two digital acoustic control systems. The digital acoustic control system on the drilling rig unit  10  includes a rig transducer  315  disposed in the water and coupled to a rig user interface station  320 , which may be operated by the drilling crew or the operator supervisor on the drilling rig unit  10 . The digital acoustic control system on a vessel near the drilling location includes an auxiliary transducer  340  coupled to an auxiliary user interface station  345 , which may be operated by a well control representative. As used herein, an independent management system refers to the auxiliary user interface station  345  with the well control representative not being managed by the drilling crew operating the rig user interface station  320 . For some embodiments, the auxiliary user interface station  345  functions concurrent with the rig user interface station  320  for possible actuation of the PCD  300  if needed. 
         [0028]    The PCD  300  having this independent management system ensures that decisions are made in a timely manner to prevent a major blowout and harm to personnel. Personnel directly involved in the well blowout on the installation, and which perhaps caused it, may not manage the PCD  300 . Independent systems from the drilling rig unit  10  mean that in the event of a large fire/explosion on the drilling rig unit  10  the PCD  300  can still be activated to protect personnel and the environment. As previously mentioned, the PCD  300  may be implemented in numerous cases, including: (1) failure of the well control system on the drilling rig unit  10 ; (2) management system failure on the drilling rig unit  10 ; or (3) fire or explosion on the drilling rig unit  10  that prevents operation or continued operation, i.e., loss of hydraulic pressure on some function, of other well control systems, such as the BOP stack  240 . 
         [0029]    In operation, signals from the rig transducer  315  or the auxiliary transducer  340  to a PCD transducer  310  or a remote transducer  335  provide command signals to the control system  303  for functioning of the PCD  300 . Both the PCD transducer  310  and the remote transducer  335  connect to the control system  303 . The remote transducer  335  may connect to the PCD  300  by a cable  325  of sufficient length (e.g., 150 meters) to enable placement of the remote transducer  335  away from the PCD transducer  310  proximate the PCD  300 . The remote transducer  335  thus may facilitate communicating with PCD  300  should access to the drilling rig unit  10  be restricted. Acoustic data transmission may also be sent from the PCD  300  to the surface via the transducers  310 ,  315 ,  335 ,  340  to monitor the system status and wellbore conditions (e.g., pressure and/or temperature measured by the transducers of the PCD  300 ). 
         [0030]    While the digital acoustic control system functions as the primary PCD control system, a secondary interface may also be utilized. In an embodiment, a remotely operated vehicle (ROV) may be utilized as a secondary PCD control system with the ROV providing physical input direct to the PCD  300  through an ROV control panel  306 . The ROV control panel  306  may send a signal to the control system  303  of the PCD  300  that operates valves sending hydraulic pressure from the power source  307  to operate the blind shear rams  301 ,  302 . 
         [0031]    PCD systems on the surface have independent controls also. Examples of such independent controls include wireless controls or shielded fiber optics, cable, or piping. Regardless of signal interface techniques employed, the independent controls enable operation of the PCD systems independent from BOP control systems. 
         [0032]    In some embodiments, the PCD facilitates capping a well almost immediately. This quick response time reduces the chance of fire or explosion endangering personnel or even sinking the drilling unit or complete loss of a fixed platform. The blowout oil spill volume is greatly reduced as the flow duration is minutes instead of weeks reducing the potential for environmental damage. 
         [0033]    There are no issues with installing the system since the PCD is preinstalled. A conventional capping stack, which is installed after a blowout, could encounter a situation where debris prevents installation. The PCD also prevents the situation where the drilling unit or platform collapses on a well due to fire and/or explosion. In this case, the blowout could not be capped with a capping stack due to debris or damage to the BOP and/or wellhead. 
         [0034]    The PCD with independent power can be operated even with significant damage to the drilling unit. The drilling unit&#39;s BOP might have failed due to loss of power but this would not impact the PCD. The PCD may include redundant blind shear rams in case one ram fails to shear the drill string and seal the well, but one ram may be sufficient if designed to shear and seal on tubulars used in the well. 
         [0035]      FIG. 4  shows a PCD  430  disposed on a wellhead  420 . The PCD  430  may function and operate as described herein with respect to  FIGS. 1-3 . In some embodiments, a BOP stack  440  couples to a top of the PCD  430  opposite the wellhead  420  and is pressure rated below a pressure rating of the PCD  430 . 
         [0036]    For example, the BOP stack  440  may be pressure rated for no more than 104 megapascals (MPa), which is sufficient for normal drilling operations where wellbore pressures are controlled with weight of mud used but may not be adequate to contain possible pressures anticipated at some wells should a blowout occur. The PCD  430  may enable safe operation even during a blowout situation by being pressure rated at the maximum anticipated pressure, such as at least 137 MPa. In some embodiments, the PCD  430  provides an at least 25 MPa or at least 50 MPa greater pressure rating than the BOP stack  440 . For some embodiments, actuation of the PCD  430  occurs upon sensing a pressure at the PCD  430  greater than a threshold pressure limit, such as the pressure rating of the BOP stack  440 . 
         [0037]    The PCD  430  thereby enables cost efficient use of commercial ready to use versions of the BOP stack  440  with wells that may experience pressures above existing pressure ratings of the BOP stack  440 . In particular, increasing pressure ratings of the BOP stack  440  increases weight of the BOP stack  440  and requires all associated equipment to handle this extra weight and also be pressure rated the same as the BOP stack  440 . The PCD  430  ensures that equipment above the PCD  430  would only be exposed to normal operating pressures and would be isolated from maximum well pressures since the PCD  430  would be operated and capable of closing the well. 
         [0038]    The pressure rating of the PCD  430  and the BOP stack  440  may utilize industry practices for qualification. For example, the PCD  430  and the BOP stack  440  may withstand one and one-half times (1.5×) the pressure for which rated without having a mechanical failure or leaking In some embodiments, the BOP stack  440  may fail or leak at pressures below those at which the PCD  430  may fail or leak or even below the pressure rating of the PCD  430 . 
         [0039]    In closing, it should be noted that the discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. At the same time, each and every claim below is hereby incorporated into this detailed description or specification as an additional embodiment of the present invention. 
         [0040]    Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims while the description, abstract and drawings are not to be used to limit the scope of the invention. The invention is specifically intended to be as broad as the claims below and their equivalents.