Pressure control in drilling operations with offset applied in response to predetermined conditions

Abstract

A method of controlling pressure in a wellbore can include determining a desired well pressure setpoint, adding an offset to the setpoint in response to an actual well pressure deviating from the setpoint by a predetermined amount, and adjusting a flow control device, thereby influencing the actual well pressure toward the setpoint plus the offset. A well system can include a flow control device which variably restricts flow from a wellbore, and a control system which determines a desired well pressure setpoint, compares the setpoint to an actual well pressure, and adds an offset to the setpoint in response to a predetermined amount of deviation between the setpoint and the actual well pressure, whereby the control system adjusts the flow control device, and thereby influences the actual well pressure toward the setpoint plus the offset.

What is claimed is: 
     
         1 . A method of controlling pressure in a wellbore in a well drilling operation, the method comprising:
 determining a desired well pressure setpoint;   adding an offset to the well pressure setpoint in response to an actual well pressure deviating from the well pressure setpoint by a predetermined amount; and   adjusting a flow control device, thereby influencing the actual well pressure toward the well pressure setpoint plus the offset.   
     
     
         2 . The method of  claim 1 , wherein the desired well pressure setpoint is output by a hydraulics model. 
     
     
         3 . The method of  claim 1 , wherein the adding is performed further in response to a predetermined level of change in flow. 
     
     
         4 . The method of  claim 3 , wherein the predetermined level of change in flow comprises a decrease in flow through the flow control device. 
     
     
         5 . The method of  claim 1 , further comprising removing the offset in response to the actual well pressure deviating from the well pressure setpoint by less than the predetermined amount. 
     
     
         6 . The method of  claim 1 , wherein the flow control device comprises a choke which restricts flow of fluid from the wellbore. 
     
     
         7 . The method of  claim 1 , further comprising controlling the flow control device, thereby influencing the actual well pressure toward the well pressure setpoint without the offset, prior to the adding. 
     
     
         8 . A well system, comprising:
 a flow control device which variably restricts flow from a wellbore; and   a control system which determines a desired well pressure setpoint, compares the well pressure setpoint to an actual well pressure, and adds an offset to the desired well pressure setpoint in response to a predetermined amount of deviation between the well pressure setpoint and the actual well pressure, whereby the control system adjusts the flow control device, and thereby influences the actual well pressure toward the well pressure setpoint plus the offset.   
     
     
         9 . The system of  claim 8 , wherein the control system comprises a hydraulics model, and wherein the well pressure setpoint is output by the hydraulics model. 
     
     
         10 . The system of  claim 8 , wherein the control system adds the offset to the well pressure setpoint further in response to a predetermined level of change in flow. 
     
     
         11 . The system of  claim 10 , wherein the predetermined level of change in flow comprises a decrease in flow through the flow control device. 
     
     
         12 . The system of  claim 8 , wherein the control system removes the offset in response to the deviation between the actual well pressure and the well pressure setpoint being less than the predetermined amount. 
     
     
         13 . The system of  claim 8 , wherein the flow control device comprises an automatically adjustable choke. 
     
     
         14 . The system of  claim 8 , wherein the control system controls the flow control device, and thereby influences the actual well pressure toward the well pressure setpoint without the offset, when the deviation between the well pressure setpoint and the actual well pressure is less than the predetermined amount. 
     
     
         15 . A method of controlling pressure in a wellbore in a well drilling operation, the method comprising:
 operating a flow control device, thereby influencing an actual well pressure toward a desired well pressure setpoint;   then adding an offset to the well pressure setpoint in response to an actual well pressure deviating from the well pressure setpoint by a predetermined amount; and   then adjusting the flow control device, thereby influencing the actual well pressure toward the well pressure setpoint plus the offset.   
     
     
         16 . The method of  claim 15 , wherein the desired well pressure setpoint is output by a hydraulics model. 
     
     
         17 . The method of  claim 15 , wherein the adding is performed further in response to a predetermined level of change in flow. 
     
     
         18 . The method of  claim 17 , wherein the predetermined level of change in flow comprises a decrease in flow through the flow control device. 
     
     
         19 . The method of  claim 15 , further comprising, after the adjusting, removing the offset in response to the actual well pressure deviating from the well pressure setpoint by less than the predetermined amount. 
     
     
         20 . The method of  claim 15 , wherein the flow control device comprises a choke which restricts flow of fluid from the wellbore.