Abstract:
The method of releasing a drilling riser depending from a surface vessel from a subsea installation, comprising unlatching a connector on the primary conduit of the drilling riser, allowing the tension in the drilling riser to cause a separation between the portion of the primary conduit above the connector and the portion of the primary conduit below the connector, and the separation causing one or more control lines to be cut into an upper portion and a lower portion.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to the general subject of a releasing connection on a subsea drilling riser which will allow the escape of a drilling rig from a blowout situation when the primary control systems have failed. 
       CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0002]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0003]    Not applicable 
       REFERENCE TO A “MICROFICHE APPENDIX” 
       [0004]    Not applicable 
       BACKGROUND OF THE INVENTION 
       [0005]    The field of this invention is that operating blowout preventers in deep water operations to seal the well bore and protect the environment in emergency situations when an obstruction is in the well bore. A surface rig is connected to the seafloor equipment by a drilling riser. When blowout conditions (the uncontrolled release of oil or gas) occur, the drilling riser becomes the conduit to deliver the oil and gas as fuel to a burning rig and can additionally anchor the rig to the seafloor. Assurance of release from the seafloor equipment can be extremely important. 
         [0006]    Blowout preventer systems are major pieces of capital equipment landed on the ocean floor in order to provide a conduit for the drill pipe and drilling mud while also providing pressure protection while drilling holes deep into the earth for the production of oil and gas. The typical blowout preventer stacks have an 18¾ inch bore and are usually of 10,000 psi working pressure. The blowout preventer stack assembly weighs in the range of five hundred to eight hundred thousand pounds. It is typically divided into a lower blowout preventer stack and a lower marine riser package. 
         [0007]    The lower blowout preventer stack includes a connector for connecting to the wellhead at the bottom on the seafloor and contains several individual ram type blowout preventer assemblies, which will close on various pipe sizes and in some cases, will close on an open hole with what are called blind rams. Characteristically there is an annular preventer at the top, which will close on any pipe size or close on the open hole. 
         [0008]    The lower marine riser package typically includes a connector at its base for connecting to the top of the lower blowout preventer stack, it contains a single annular preventer for closing off on any piece of pipe or the open hole, a flex joint, and a connection to a riser pipe which extends to the drilling vessel at the surface. 
         [0009]    The purpose of the separation between the lower blowout preventer stack and the lower marine riser package is that the annular blowout preventer on the lower marine riser package is the preferred and most often used pressure control assembly. When it is used and either has a failure or is worn out, it can be released and retrieved to the surface for servicing while the lower blowout preventer stack maintains pressure competency and remains at the wellhead on the ocean floor. 
         [0010]    The riser pipe extending to the surface is typically a 21 inch O.D. pipe with a bore larger than the bore of the blowout preventer stack. It is a low pressure pipe and will control the mud flow which is coming from the well up to the rig floor, but will not contain the 10,000-15,000 psi that the typical blowout preventer stack will contain. Whenever high pressures must be communicated back to the surface for well control procedures, smaller pipes on the outside of the drilling riser, called the choke line and the kill line, provide this function. These will typically have the same working pressure as the blowout preventer stack and rather than have an 18¾-20 inch bore, they will have a 3-4 inch bore. There may be additional lines outside the primary pipe for delivering hydraulic fluid for control of the blowout preventer stack or boosting the flow of drilling mud back up through the drilling riser. 
         [0011]    The blowout preventers are operated or closed in response to an electric signal from the surface to an electro-hydraulic control valve which directs fluid stored under pressure in accumulator bottles to the operating cylinders on the blowout preventer. Any number of events can prevent this sequence from occurring such as failure in the surface controls to send the signal, failure in the connecting lines from the surface to depth as great as 12,000′, failure of the electro-hydraulic valve to close, and absence of fluid stored under pressure. 
         [0012]    All subsea blowout preventers have 100% redundant control systems to minimize the risk of non-operation. They are very characteristically called the yellow system and blue system and represent primary and secondary means to operate any function on the blowout preventer stack. 
         [0013]    When all else fails, it is not necessary to have emergency operation of multiple components in the subsea blowout preventer stack. A single component—the blind shear rams can immediately secure an uncontrolled flow of oil or gas from the well. A flat faced gate from each side will meet at the middle to seal off the bore. If a pipe of any sort is in the bore at the time, it will simply shear the pipe in half and then seal. The blind shear ram is the ultimate safety device, but it must operate. 
         [0014]    Ultimately, if all fails, there can be an uncontrolled release of oil and gas up the bore of the drilling riser with disastrous results on the surface vessel. 
       BRIEF SUMMARY OF THE INVENTION 
       [0015]    The object of this invention is to provide a method of emergency release of the vessel from a subsea blowout preventer stack when the well is blowing out. 
         [0016]    A second object of this invention is to close off the bottom of the released riser to prevent the release of the drilling mud to the environment. 
         [0017]    A third object of this invention is to close off the bottom of the released riser to prevent the release of heavy drilling mud which can cause a collapse of the riser near the surface. 
         [0018]    Another object of this invention is to provide for cutting of any pipe within the drilling riser to facilitate movement away from the cut riser portion, 
         [0019]    Another object of this invention is to provide for cutting of control lines which are tying the vessel to the subsea blowout preventer stack. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a view of a deepwater drilling system such as would use this invention 
           [0021]      FIG. 2  is a view of the deepwater drilling system separated at the connection of the present invention. 
           [0022]      FIG. 3  is a close-up view of the connection of the present invention in the normal drilling mode. 
           [0023]      FIG. 4  is a close-up view of the connection of the present invention after being released. 
           [0024]      FIG. 5  is a half section of the connection of the present invention in the normal drilling mode as was seen in  FIGS. 1 and 3 . 
           [0025]      FIG. 6  is a half section of the connection of the present invention after being released as was seen in  FIGS. 2 and 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    Referring now to  FIG. 1 , a view of a complete system for drilling subsea wells  20  is shown in order to illustrate the utility of the present invention. The drilling riser  22  is shown with a central pipe  24 , outside fluid lines  26 , and control lines  28 . 
         [0027]    Below the drilling riser  22  is a flex joint  30 , lower marine riser package  32 , lower blowout preventer stack  34  and wellhead  36  landed on the seafloor  38 . 
         [0028]    Below the wellhead  36 , it can be seen that a hole was drilled for a first casing string, that string  40  was landed and cemented in place, a hole drilled through the first string for a second string, the second casing string  42  cemented in place, and a hole is being drilled for a third casing string by drill bit  44  on drill string  46 . 
         [0029]    The lower blowout preventer stack  22  generally comprises a lower hydraulic connector for connecting to the subsea wellhead system  36 , usually 4 or 5 ram style blowout preventers, an annular preventer, and an upper mandrel for connection by the connector on the lower marine riser package  32 . 
         [0030]    Below outside fluid line  26  is a choke and kill (C&amp;K) connector  50  and a pipe  52  which is generally illustrative of a choke or kill line. Pipe  52  goes down to valves  54  and  56  which provide flow to or from the central bore of the blowout preventer stack as may be appropriate from time to time. Typically a kill line will enter the bore of the Blowout Preventers below the lowest ram and has the general function of pumping heavy fluid to the well to overburden the pressure in the bore or to “kill” the pressure. The general implication of this is that the heavier mud will not be circulated, but rather forced into the formations. A choke line will typically enter the well bore above the lowest ram and is generally intended to allow circulation to circulate heavier mud into the well to regain pressure control of the well. 
         [0031]    Normal drilling circulation is the mud pumps  60  taking drilling mud  62  from tank  64 . The drilling mud will be pumped up a standpipe  66  and down the upper end  68  of the drill string  46 . It will be pumped down the drill string  46 , out the drill bit  44 , and return up the annular area  70  between the outside of the drill string  46  and the bore of the hole being drilled, up the bore of the casing  42 , through the subsea wellhead system  36 , the lower blowout preventer stack  34 , the lower marine riser package  32 , up the drilling riser  24 , out a bell nipple  72  and back into the mud tank  64 . 
         [0032]    During situations in which an abnormally high pressure from the formation has entered the well bore, the thin walled drilling riser  24  is typically not able to withstand the pressures involved. Rather than making the wall thickness of the relatively large bore drilling riser thick enough to withstand the pressure, the flow is diverted to a choke line  26 . It is more economic to have a relatively thick wall in a small pipe to withstand the higher pressures than to have the proportionately thick wall in the larger riser pipe. 
         [0033]    When higher pressures are to be contained, one of the annular or ram blowout preventers are closed around the drill pipe and the flow coming up the annular area around the drill pipe is diverted out through choke valve  54  into the pipe  52 . The flow passes up through C&amp;K connector  50 , up pipe  26  which is attached to the outer diameter of the riser  24 , through choking means illustrated at  74 , and back into the mud tanks  64 . 
         [0034]    On the opposite side of the drilling riser  24  is shown a cable or hose  28  coming across a sheave  80  from a reel  82  on the vessel  84 . The cable  28  is shown characteristically entering the top of the lower marine riser package. These cables typically carry hydraulic, electrical, multiplex electrical, or fiber optic signals. Typically there are at least two of these systems, which are characteristically painted yellow and blue. As the cables or hoses  28  enter the top of the lower marine riser package  32 , they typically enter the top of control pod to deliver their supply or signals. When hydraulic supply is delivered, a series of accumulators are located on the lower marine riser package  32  or the lower blowout preventer stack  34  to store hydraulic fluid under pressure until needed. 
         [0035]    Release joint  90  has release joint upper portion  92  and release joint lower portion  94  are shown above flex joint  30  and contain components necessary to release the drilling riser  22  and vessel  84  from the subsea well  20  in emergency conditions. 
         [0036]    Referring now to  FIG. 2  release joint upper portion  92  is shown released from the release joint lower portion  94  and the vessel is shown as moving towards the right on the page. Drill string  46  is shown as cut, with a portion of the drill string  96  remaining inside the release joint lower portion  94 . It can be noted that the remaining portion of the drill string  46  within the upper part of the drilling riser  22  has naturally moved upwardly because it was in tension. 
         [0037]    Referring now to  FIG. 3 , release joint  90  is shown with an upper flange  100  engaging the lower flange  102  of a riser joint and lower flange  104  engaging the upper flange  106  of a riser joint  24  or the flex joint  30 . A central connector  110  is shown and supports a cutter blade  112 . A mating cutter blade  114  is mounted on an upper body  116 . Control cable  120  is positioned between the cutter blades  112  and  114  by brackets at  122  and  124 . An auxiliary line connection  130  is shown which illustrates what a choke line, a kill line, or a booster line might look like. Explosive or chemical cutter  132  is shown mounted on a pivot at  134 . 
         [0038]    Referring now to  FIG. 4 , release joint upper portion  92  is shown released from the release joint lower portion  94 . Upper body  116  is raised above central connector  110  and valve restraining sleeve  140  is shown. Drill string  46  has been cut into upper portion  142  and lower portion  144  by explosive or chemical cutter  132  as it was released and pivoted down about pivot  134 . Backstop  146  is seen opposite the bore from explosive or chemical cutter  132  as a safety precaution in case it is accidentally activated on the surface and personnel are in the area. Auxiliary connection  130  (illustrated in  FIG. 3 ) is separated into a box member  150  and pin member  152 . This is preferably a straight stab with seal which pulls out when the upper body  116  is raised. Control cable  120  is cut into upper portion  154  and lower portion  156 . As a result of these separations and cuttings, the release joint upper portion  92  is released from the released joint lower portion  94  and therefore the vessel  84  (illustrated in  FIG. 2 ) is free to move away from danger. 
         [0039]    Referring now to  FIG. 5 , auxiliary line connection  130  is shown with a flapper valve  160  which is held open by the pin member  152 . Upper body  116  is shown to house a finger valve  162  which is held in the open position by restraining sleeve  140 . Explosive or chemical cutter  132  is held in a first position by the outer surface  164  of central connector  110 . Firing mechanism  166  is a push button which is designed to not activate when explosive or chemical cutter  132  is engaged by outer surface  164 . However, when firing mechanism engages a diameter smaller diameter than outer surface  164 , it will cause the explosive or chemical cutter  132  to activate and cut the smaller diameter pipe. Central connector  110  pistons  170  and locking dogs  172  as are discussed in U.S. Pat. No. 6,609,734. 
         [0040]    Referring now to  FIG. 6 , the central connector  110  has been released and release joint upper portion  92  is shown released from the release joint lower portion  94 . Drill string upper portion  142  is shown as being moved higher within the release joint upper portion  92  as would be expected with the normal tension of the drill pipe. The absence of drill pipe from within the lower portion of the release joint upper portion  92  allows the finger valve  162  to close and trap the mud within the riser. Finger valve  162  is shown with 8 pie shaped finger sections  170  which have a metal core  172  for strength and area coated with rubber  174  for sealing. Each adjacent finger section  170  is engaged by a square profile  176  similar to a common wobble extension for a ratchet tool set to cause all sections to close together. Similarly, as the pin member  152  is removed from the box member  150 , the flapper valve  160  will be allowed to close and trap the drilling mud within the auxiliary pipe. 
         [0041]    At this time all connections between the upper portion of the drilling riser and the lower portion of the drilling riser have been released or severed, allowing the vessel to be moved to safety. 
         [0042]    Line  180  brings hydraulic fluid from control valve  182  to unlatch central connector  110  and line  184  sends hydraulic fluid from control valve  182  to latch central connector  110 . Hydraulic supply is preferably from one or more dedicated accumulators  186  so that their capacity cannot be depleted by other operations. Control valve  182  is moved to the unlatching position as shown by a spring  188  upon the loss of an electric signal to solenoid  190 . 
         [0043]    The signal can come along wire  192  from a control module  194  which is battery  196  powered so that it can be functional after all other control signals are lost. The control module  194  can be armed by the concurrent receipt of a signal from blue control system  196  along wire  198  and yellow control system  200  along wire  202 . Blue control system  196  and yellow control system  200  are iconic of the control systems on every subsea blowout preventer system. When the arming signal is lost from both of the control systems, the control module  194  can go into a firing sequence. A typical sequence might be to send an alarming signal back through both control systems and back to the surface to notify that if it does not receive a disarm signal within 3 minutes, it will actuate control valve  182  and send fluid pressure from accumulators  186  to unlatch the central connector  110  as described above. 
         [0044]    The non-obviousness of this invention is clearly demonstrated by the need for enhanced safety in emergency situations, the extended period over which the need has been known, and the lack of recognition of this solution to the problem. 
         [0045]    The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.