Pressure and flow control in continuous flow drilling operations

Abstract

A method of providing substantially continuous circulation of fluid through a drill string and an annulus can include sealing off the annulus from atmosphere, regulating flow of the fluid from the annulus, thereby controlling pressure in the wellbore, and diverting flow of the fluid from a pump to an uppermost connector of the drill string and an inlet extending in a sidewall of the drill string, the regulating and the diverting being performed concurrently. A pressure and flow control system can include one or more flow control devices which divert flow from a pump to a valve which selectively permits and prevents communication between an uppermost connector of the drill string and a flow passage extending longitudinally through the drill string, and to a valve which selectively permits and prevents communication between the flow passage and an inlet extending in a sidewall of the drill string.

What is claimed is: 
     
         1 . A method of providing substantially continuous circulation of fluid through a drill string and an annulus between the drill string and a wellbore, the method comprising:
 operating a hydraulics model; and   in response to an output from the hydraulics model, diverting flow of the fluid from a pump to:
 a) an uppermost connector of the drill string, and 
 b) an inlet extending in a sidewall of the drill string, 
   wherein each of the uppermost connector and the inlet is communicable with a flow passage extending longitudinally through the drill string.   
     
     
         2 . The method of  claim 1 , wherein the diverting further comprises gradually decreasing the flow of the fluid from the pump to the uppermost connector while gradually increasing the flow of the fluid from the pump to the inlet. 
     
     
         3 . The method of  claim 1 , wherein the diverting further comprises gradually increasing the flow of the fluid from the pump to the uppermost connector while gradually decreasing the flow of the fluid from the pump to the inlet. 
     
     
         4 . The method of  claim 1 , wherein the pressure in the wellbore is maintained substantially constant throughout the diverting. 
     
     
         5 . The method of  claim 1 , wherein the diverting further comprises automatically operating at least one flow control device which controls flow to the uppermost connector, and which controls flow to the inlet. 
     
     
         6 . The method of  claim 1 , wherein a substantially constant flow of the fluid through the drill string and the annulus is maintained throughout the diverting. 
     
     
         7 . The method of  claim 1 , wherein the diverting further comprises diverting the flow of the fluid from the pump to an outlet line via which the fluid flows from the annulus. 
     
     
         8 . A pressure and flow control system for providing substantially continuous circulation of fluid from a pump through a drill string and an annulus between the drill string and a wellbore, the system comprising:
 at least one flow control device which diverts flow from the pump to:
 a) a first valve which selectively permits and prevents communication between an uppermost connector of the drill string and a flow passage extending longitudinally through the drill string, and 
 b) a second valve which selectively permits and prevents communication between the flow passage and an inlet extending in a sidewall of the drill string; and 
   an annular seal device which seals off the annulus while the at least one flow control device diverts flow between the first and second valves.   
     
     
         9 . The system of  claim 8 , wherein the at least one flow control device comprises first and second chokes, wherein the first choke variably regulates flow from the pump to the first valve, and wherein the second choke variably regulates flow from the pump to the second valve. 
     
     
         10 . The system of  claim 9 , wherein the first and second chokes are operated in response to sensor inputs to a hydraulics model. 
     
     
         11 . The system of  claim 9 , wherein the first and second chokes are operated simultaneously, whereby flow is gradually diverted between the first and second valves. 
     
     
         12 . The system of  claim 8 , wherein the first and second valves are operated in response to sensor inputs to a hydraulics model. 
     
     
         13 . The system of  claim 8 , wherein the at least one flow control device is automatically operated and maintains a substantially constant flow of the fluid through the drill string and the annulus while flow is diverted between the first and second valves. 
     
     
         14 . The system of  claim 8 , wherein the at least one flow control device further diverts the flow of the fluid from the pump to an outlet line via which the fluid flows from the annular seal device. 
     
     
         15 . A method of providing substantially continuous circulation of fluid through a drill string and an annulus between the drill string and a wellbore, the method comprising:
 inputting sensor measurements to a hydraulics model; and   in response to an output of the hydraulics model, automatically operating at least one flow control device, thereby diverting flow of the fluid from a pump to:
 a) a first valve which selectively permits and prevents communication between an uppermost connector of the drill string and a flow passage extending longitudinally through the drill string, and 
 b) a second valve which selectively permits and prevents communication between the flow passage and an inlet extending in a sidewall of the drill string. 
   
     
     
         16 . The method of  claim 15 , wherein the diverting further comprises gradually decreasing the flow of the fluid from the pump to the first valve while gradually increasing the flow of the fluid from the pump to the second valve. 
     
     
         17 . The method of  claim 15 , wherein the diverting further comprises gradually increasing the flow of the fluid from the pump to the first valve while gradually decreasing the flow of the fluid from the pump to the second valve. 
     
     
         18 . The method of  claim 15 , wherein the pressure in the wellbore is maintained substantially constant throughout the diverting. 
     
     
         19 . The method of  claim 15 , wherein a substantially constant flow of the fluid through the drill string and the annulus is maintained throughout the diverting. 
     
     
         20 . The method of  claim 15 , wherein the diverting further comprises diverting the flow of the fluid from the pump to an outlet line via which the fluid flows from the annulus.