Method of operating a drilling system

Abstract

A method of operating a drilling system. The drilling system includes a drill string extending into a wellbore, a driver which rotates the drill string, a pump to pump drilling fluid down the drill string, a wellhead mounted at the wellbore, a riser extending up from the wellhead around the drill string, a blowout preventer mounted on the wellhead, a riser closure device mounted in the riser, a first return conduit, and a flow outlet arranged in the riser below the riser closure device. The method includes operating the driver to stop a rotation of the drill string, closing the riser closure device if it is not already closed, operating the pump to stop a pumping of drilling fluid down the drill string, closing the blowout preventer, and increasing a wellbore pressure by controlling a rate of the flow of the fluid along the first return conduit.

What is claimed is: 
     
         1 - 33 . (canceled) 
     
     
         34 . A method of operating a drilling system,
 the drilling system comprising:
 a drill string which extends into a wellbore; 
 a driver configured to rotate the drill string; 
 a pump configured to pump drilling fluid down the drill string; 
 a wellhead mounted at a top of the wellbore; 
 a riser configured to extend up from the wellhead around the drill string so as to provide a riser annulus between the riser and the drill string; 
 a blowout preventer mounted on the wellhead, the blowout preventer being configured to close around the drill string so as to substantially prevent a flow of a fluid from an annular space around the drill string in the wellbore into the riser annulus, the blowout preventer comprising a sealing element which is configured to engage with the drill string when the blowout preventer is operated to close around the drill string; 
 a riser closure device mounted in the riser, the riser closure device being configured to close around the drill string so as to substantially prevent the flow of the fluid along the riser annulus; 
 a first return conduit; and 
 a flow outlet arranged in the riser below the riser closure device, the flow outlet being configured to connect the riser annulus to the first return conduit, 
   wherein, after determining that there is or may be a need to close the blowout preventer, the method of operating the drilling system implements a control procedure comprising the steps:   a) operating the driver to stop a rotation of the drill string;   b) closing the riser closure device if the riser closure device is not already closed;   c) operating the pump to stop a pumping of drilling fluid down the drill string;   d) closing the blowout preventer; and   e) increasing a wellbore pressure by controlling a rate of the flow of the fluid along the first return conduit.   
     
     
         35 . The method as recited in  claim 34 , wherein step e) comprises increasing the wellbore pressure to bring the wellbore pressure up towards, to, or above a pore pressure of a formation causing an influx into the wellbore. 
     
     
         36 . The method as recited in  claim 34 , wherein step e) comprises increasing the wellbore pressure to compensate for a reduction in the wellbore pressure resulting from at least one of step a) and step c). 
     
     
         37 . The method as recited in  claim 34 , wherein the drilling system further comprises:
 a flow restriction device mounted in the first return conduit, the flow restriction device being configured to vary an extent to which the flow of the fluid along the first return conduit is restricted.   
     
     
         38 . The method as recited in  claim 37 , wherein step e) comprises increasing a back pressure on the riser annulus by operating the flow restriction device to increase the extent to which the flow of fluid along the first return conduit is restricted. 
     
     
         39 . The method as recited in  claim 34 , wherein step e) is performed before performing step d). 
     
     
         40 . The method as recited in  claim 34 , wherein,
 step e) is performed before performing step a), or   step e) is performed at the same time as performing step a), or   step e) is performed after performing step a).   
     
     
         41 . The method as recited in  claim 34 , wherein step e) is performed at the same time as performing step c). 
     
     
         42 . The method as recited in  claim 34 , wherein,
 step a) is performed before performing step b), and   step b) is performed before performing step c).   
     
     
         43 . The method as recited in  claim 34 , wherein step d) is performed after performing step a), step b), and step c). 
     
     
         44 . The method as recited in  claim 34 , wherein the method further comprises the step of:
 f) lifting the drill string off a bottom of the wellbore.   
     
     
         45 . The method as recited in  claim 44 , wherein step f) is performed before performing step a). 
     
     
         46 . The method as recited in  claim 44 , wherein the method further comprises the step of:
 g) performing a flow check.   
     
     
         47 . The method as recited in  claim 46 , wherein step g) is performed after performing step c). 
     
     
         48 . The method as recited in  claim 46 , wherein step g) is performed after performing step a). 
     
     
         49 . The method as recited in  claim 46 , wherein,
 the drilling system further comprises:
 a BOP to riser conduit which connects a lower annular space around the drill string below the sealing element of the blowout preventer with an upper annular space around the drill string above the sealing element of the blowout preventer, the BOP to riser conduit comprising a valve which is movable between an open position in which a flow of the fluid along the BOP to riser conduit from the lower annular space to the upper annular space is permitted, and a closed position in which the flow of the fluid along the BOP to riser conduit is prevented, and 
   the method further comprising the steps of:
 h) opening the valve in the BOP to riser conduit; and 
 i) closing the valve in the BOP to riser conduit. 
   
     
     
         50 . The method as recited in  claim 49 , wherein step h) is performed before performing step d). 
     
     
         51 . The method as recited in  claim 50 , wherein step h) is performed before performing step a). 
     
     
         52 . The method as recited in  claim 50 , wherein step h) is performed after performing step a) and step b), and before performing step d). 
     
     
         53 . The method as recited in  claim 49 , wherein step d) is performed before performing step c). 
     
     
         54 . The method as recited in  claim 49 , wherein step i) is performed after performing step c). 
     
     
         55 . The method as recited in  claim 49 , wherein step e) comprises increasing a rate of operation of the pump. 
     
     
         56 . The method as recited in  claim 49 , wherein,
 the drilling system further includes:
 a second return conduit configured to extend from an outlet arranged at the lower annular space around the drill string below the sealing element of the blow out preventer, and 
 a valve arranged in the second return conduit, the valve normally being closed so as to prevent a flow of the fluid along the second return conduit, but which is configured to allow or to prevent the flow of the fluid along the second return conduit, and 
   the method further comprises the step of:
 j) opening the valve in the second return conduit. 
   
     
     
         57 . The method as recited in  claim 56 , wherein step j) is performed after each of step a), step b), step c), step d), step e), step f), step g), step h), and step i). 
     
     
         58 . The method as recited in  claim 56 , wherein,
 each of the first return conduit and the second return conduit comprise an isolation valve which is configured to be movable between a closed position in which the flow of the fluid along the respective first return conduit and second return conduit is substantially prevented, and an open position which the flow of the fluid along the respective first return conduit and second return conduit is permitted, and   the method further comprises the step of:
 k) moving each isolation valve from the closed position to the open position immediately prior to performing step b). 
   
     
     
         59 . The method as recited in  claim 58 , wherein the drilling system further comprises:
 a riser booster pump arranged at a lower end of the riser; and   a riser booster conduit which is configured to extend from the riser booster pump,   wherein,   the riser booster pump is operated at all times while performing the method to pump drilling fluid into the lower end of the riser.   
     
     
         60 . The method as recited in  claim 34 , wherein,
 the drilling system further comprises a flow spool, and   the flow outlet is arranged in the flow spool.   
     
     
         61 . The method as recited in  claim 60 , wherein,
 the drilling system further comprises a slip joint via which the riser is suspendable from a drilling rig.   
     
     
         62 . The method as recited in  claim 61 , wherein the riser closure device is located between the flow outlet and the slip joint. 
     
     
         63 . The method as recited in  claim 61 , wherein,
 the drilling system further comprises a diverter mounted in an upper portion of the riser above the slip joint, and   the flow outlet is arranged in the flow spool between the slip joint and the diverter.