Choke system

Abstract

A method and apparatus for controlling pressure in a drilling system that includes a drilling fluid return flow path. Steps include providing a choke system comprising a first flowline having an inlet and an outlet each connected to the drilling fluid return flow path, wherein the outlet connects to the return flow path downstream of the inlet connection, a first choke positioned on the flowline, a second choke positioned on the flowline downstream of the first choke, and a control module for controlling the first and second chokes; flowing drilling fluid through the first flowline while at least one of the first and second choke is partially closed so as to cause a pressure drop; in response to an input, opening the partially closed choke and partially closing the other choke so as to substantially maintain the pressure drop; returning the chokes to the original flow status.

What is claimed is: 
     
         1 . A choke system for controlling pressure in drilling system that includes a drilling fluid return flow path, the choke system comprising:
 a first flowline having an inlet and an outlet that are each connected to the drilling fluid return flow path, wherein the outlet connects to the drilling fluid return flow path at a point that is downstream in the drilling fluid return flow path of the inlet connection;   a first choke positioned on the flowline;   a second choke positioned on the flowline downstream of the first choke; and   a system for controlling the first and second chokes.   
     
     
         2 . The choke system of  claim 1 , further including a second flowline connected to the drilling fluid return flow path in parallel with the first flowline, the second flowline including at least two additional chokes arranged in series. 
     
     
         3 . The choke system of  claim 1  wherein the first flowline includes at least three chokes arranged in series. 
     
     
         4 . The choke system of  claim 1 , further including a rotating control device (RCD) or pressure control device (PCD) comprising at least one rotating sealing element and a housing defining a flow path that forms part of the drilling fluid return flow path, wherein the first flowline inlet is in fluid communication with the flow path at a point upstream of the rotating sealing element and the first flowline outlet is in fluid communication with the flow path at a point downstream of the rotating sealing element. 
     
     
         5 . The choke system of  claim 4 , further including a second flowline connected to the RCD flow path in parallel with the first flowline, the second flow line including at least two additional chokes arranged in series. 
     
     
         6 . A drilling riser including the choke system of  claim 1  incorporated as part of the riser. 
     
     
         7 . The choke system of  claim 1 , wherein the choke system is incorporated into a hydrocarbon production drilling system or geothermal drilling system. 
     
     
         8 . A drilling system for a rig having mud handling system, comprising:
 a riser;   a rotating control device (RCD) installed in the riser; and   a choke system according to  claim 1  in fluid communication with the RCD so that fluid flow through the riser can bypass the RCD via the choke system;   wherein the fluid flow from the choke system is adapted to be routed back into the riser and the mud handling system.   
     
     
         9 . A method for controlling pressure in a drilling production system that includes a drilling fluid return flow path, the method comprising:
 a) providing a choke system comprising:
 a first flowline having an inlet and an outlet each connected to the drilling fluid return flow path, wherein the outlet connects to the drilling fluid return flow path at a point that is downstream in the drilling fluid return flow path of the inlet connection; 
 a first choke positioned on the flowline; 
 a second choke positioned on the flowline downstream of the first choke; and 
 a control module for controlling the first and second chokes; 
   b) flowing drilling fluid through the first flowline while at least one of the first and second choke is partially closed so as to cause a predetermined pressure drop between the inlet and the outlet;   c) in response to a predetermined input, flowing drilling fluid through the first flowline while fully opening the partially closed choke of step b) and partially closing the other choke so as to substantially maintain the predetermined pressure drop;   d) flowing drilling fluid through the first flowline while returning the first and second chokes to the flow status of step b); and   e) repeating steps b)-d).   
     
     
         10 . The method of  claim 9  wherein the predetermined input is a time input. 
     
     
         11 . The method of  claim 9  wherein the predetermined input is a pressure change in the drilling fluid return flow path. 
     
     
         12 . The method of  claim 9  wherein the predetermined input is a pressure change in the first flowline. 
     
     
         13 . The method of  claim 9  wherein the choke system further includes a second flowline connected to the drilling fluid return flow path in parallel with the first flowline, the second flowline including at least two additional chokes arranged in series, and further including flowing drilling fluid through the second flowline and opening and closing the additional chokes while maintaining the predetermined pressure drop. 
     
     
         14 . The method of  claim 13  wherein at least one flowline includes at least three chokes arranged in series and wherein at least one of the at least three chokes is partially closed at each step. 
     
     
         15 . The method of  claim 9  wherein step a) includes providing a rotating control device (RCD) comprising at least one rotating sealing element and a housing defining an RCD flow path that forms part of the drilling fluid return flow path, wherein the first flowline inlet is in fluid communication with the RCD flow path at a point upstream of the sealing element and the first flowline outlet is in fluid communication with the RCD flow path at a point downstream of the sealing element, and wherein step b) includes flowing drilling fluid through the RCD flow path. 
     
     
         16 . The method of  claim 15 , further including a second flowline connected to the RCD flow path in parallel with the first flowline, the second flowline including at least two additional chokes arranged in series. 
     
     
         17 . The method of  claim 15 , further comprising controlling the chokes in steps b)-d) such that the pressure drop between the inlet and the outlet varies from the predetermined pressure drop by less than 10 bar.