Apparatus, System, and Method for Controlling the Flow of Drilling Fluid in a Wellbore

Abstract

A drilling system includes a drill string extending through a BOP and a drilling fluid discharge coupling mounted to the BOP. In addition, the drilling system includes a drilling fluid control system configured to control a pressure or flow rate of a drilling fluid flowing through the discharge coupling. The drilling fluid control system includes a flow rate and pressure regulating device, a feedback controller system configured to operate the regulating device, and a first sensor configured to measure an actual pressure or flow rate of the drilling fluid flowing through the discharge coupling.

What is claimed is: 
     
         1 . A drilling system for forming a borehole in an earthen formation, the drilling system comprising:
 a drill string extending through a blowout preventer;   a drilling fluid discharge coupling mounted to the blowout preventer;   a drilling fluid control system configured to control a pressure or flow rate of a drilling fluid flowing through the discharge coupling;   wherein the drilling fluid control system includes a flow rate and pressure regulating device, a feedback controller system configured to operate the regulating device, and a first sensor configured to measure an actual pressure or flow rate of the drilling fluid flowing through the discharge coupling;   wherein the regulating device includes a drilling fluid inlet in fluid communication with the discharge coupling, a drilling fluid outlet, an annular cage positioned between the inlet and the outlet, a valve plug slidingly disposed within the cage, an actuator, and a second sensor;   wherein the actuator is configured to adjust an axial position of the valve plug relative to the cage to selectively control the flow of drilling fluid through the cage from the inlet to the outlet, and the second sensor is configured to measure an actual axial position of the valve plug relative to the cage,   wherein the feedback controller system is configured to receive a desired pressure or flow rate and includes a process control engine configured to adjust the axial position of the valve plug relative to the cage based on a comparison of the actual pressure or flow rate measured by the first sensor and the desired pressure or flow rate and based on a comparison of the actual change in the axial position of the valve plug relative to the cage measured by the second sensor and a desired change in the axial position.   
     
     
         2 . The drilling system of  claim 1 , wherein the process control engine is configured to:
 determine a desired change in the axial position of the valve plug relative to the cage based on a comparison of the desired pressure or flow rate and the measured pressure or flow rate from the first sensor;   adjust the axial position of the valve plug relative to the cage with the actuator based on the desired change in the axial position of the valve plug;   determine an actual change in the axial position of the valve plug relative to the cage based on the measured axial positions from the second sensor; and   compare the desired change in the axial position of the valve plug relative to the cage to the actual change in the axial position valve plug relative to the cage while adjusting the axial position of the valve plug relative to the cage with the actuator.   
     
     
         3 . The drilling system of  claim 2 , wherein the actuator includes a threaded shaft, a sleeve threaded onto the threaded shaft and coupled to the valve plug, and a motor configured to rotate the threaded shaft relative to the sleeve. 
     
     
         4 . The drilling system of  claim 3 , wherein the second sensor is a rotary resolver. 
     
     
         5 . The drilling system of  claim 1 , wherein the process control engine is configured to determine a gain based on the comparison of the desired pressure or flow rate and the measured pressure or flow rate, and adjust a speed of the change in the axial position of the valve plug relative to the cage based on the gain. 
     
     
         6 . The drilling system of  claim 2 , wherein the feedback controller system further includes a user interface configured for inputting the desired pressure or flow rate and configured to display the actual pressure or flow rate of the drilling fluid disposed within the discharge coupling measured with the first sensor. 
     
     
         7 . The drilling system of  claim 2 , wherein the cage includes a plurality of circumferentially spaced apertures in fluid communication with the drilling fluid inlet, wherein the valve plug is configured to control the flow of drilling fluid through the apertures. 
     
     
         8 . A method for controlling the pressure or flow rate of drilling fluid flowing from a borehole through a valve, the method comprising:
 (a) measuring the pressure or flow rate of the drilling fluid;   (b) obtaining a desired pressure or flow rate for the drilling fluid;   (c) comparing the measured pressure or flow rate with the desired pressure or flow rate;   (d) determining a desired change in an axial position of a valve plug within the valve based on the comparison in (c);   (e) adjusting the axial position of the valve plug based on the desired change in the axial position of the valve plug in (d);   (f) determining an actual change in the axial position of the valve plug during (e); and   (g) comparing the actual change in the axial position of the valve plug with the desired change in the axial position of the valve plug during (e).   
     
     
         9 . The method of  claim 8 , further comprising:
 (h) adjusting the axial position of the valve plug based on the comparison of the desire change in the axial position and the actual change in the axial position in (g).   
     
     
         10 . The method of  claim 8 , wherein (a) comprises measuring the pressure or flow rate of the drilling fluid with a first sensor disposed upstream of the valve; and
 wherein (f) comprises measuring the axial position of the valve plug with a position sensor coupled to the valve plug.   
     
     
         11 . The method of  claim 8 , further comprising:
 adjusting a speed of the change in the axial position in (e) based on the comparison the measured pressure or flow rate and the desired pressure or flow rate in (c).   
     
     
         12 . The method of  claim 11 , wherein adjusting the speed of the change in the axial position comprises selecting a gain based on the comparison the measured pressure or flow rate and the desired pressure or flow rate in (c). 
     
     
         13 . The method of  claim 8 , wherein (b) comprises inputting the desired pressure or flow rate at a user interface. 
     
     
         14 . The method of  claim 8 , wherein (e) comprises:
 sending an actuator control signal to an actuator of the valve; and   rotating a threaded shaft in the valve with the actuator.   
     
     
         15 . The method of  claim 8 , wherein the desired change in the axial position of the valve plug is a function of the difference between the measured pressure or flow rate and the desired pressure or flow rate. 
     
     
         16 . A method for controlling the pressure or flow rate of drilling fluid flowing from a borehole through a flow rate and pressure regulating device, the method comprising:
 utilizing a first control loop to determine a desired change in a position of a valve plug within the regulating device to achieve a desired pressure or flow rate of the drilling fluid; and   utilizing a second control loop to adjust the actual position of the valve plug within the regulating device based on the desired change in the position of the valve plug from the first control loop.   
     
     
         17 . The method of  claim 16 , further comprising:
 communicating the desire pressure or flow rate of the drilling fluid from a user interface to the first control loop.   
     
     
         18 . The method of  claim 16 , further comprising utilizing the first control loop to determine a gain that influences a speed for the desired change in position of the valve plug. 
     
     
         19 . The method of claim C 3 , wherein the second control loop adjusts the speed of the change in the actual position of the valve plug based on the gain determined by the first control loop. 
     
     
         20 . The method of  claim 16  wherein first control loop comprises a first sensor configured to provide feed-back about the pressure or flow rate of drilling fluid, a first controller, and a first actuator;
 wherein the second control loop comprises a second sensor, a second controller, and a second actuator. 
 wherein the first actuator comprises the second control loop.