Method of operating a drilling system

Abstract

A method of operating a drilling system for drilling a subterranean bore hole. The drilling system includes a drill string which rotates during a drilling, and a sealing device which provides a substantially fluid tight seal around the drill string while the drill string is rotating during the drilling. The method includes injecting a fluid into an annular volume around the drill string directly above the sealing device, and controlling a first fluid pressure in the annular volume around the drill string above the sealing device so that the first fluid pressure is greater than a second fluid pressure in the annular volume around the drill string directly below the sealing device.

What is claimed is: 
     
         1 - 35 . (canceled) 
     
     
         36 . A method of operating a drilling system for drilling a subterranean bore hole, the drilling system comprising:
 a drill string configured to rotate during a drilling; and   a first sealing device configured to provide a substantially fluid tight seal around the drill string while the drill string is rotating during the drilling,   the method comprising:   injecting a fluid into an annular volume around the drill string directly above the first sealing device; and   controlling a first fluid pressure in the annular volume around the drill string above the first sealing device so that the first fluid pressure is greater than a second fluid pressure in the annular volume around the drill string directly below the first sealing device.   
     
     
         37 . The method as recited in  claim 36 , wherein,
 the drilling system further comprises a second sealing device arranged below the first sealing device, the second sealing device being configured to provide a substantially fluid tight seal around the drill string while the drill string is rotating during the drilling,   the injecting step includes injecting the fluid into the annular volume around the drill string between the first sealing device and the second sealing device, and   the controlling step includes controlling a third fluid pressure in the annular volume around the drill string between the first sealing device and the second sealing device so that the third fluid pressure is greater than the second fluid pressure in the annular volume around the drill string directly below the second sealing device.   
     
     
         38 . The method as recited in  claim 37 , wherein the controlling step includes controlling the third fluid pressure in the annular volume around the drill string between the first sealing device and the second sealing device so that the third fluid pressure is greater than the first fluid pressure in the annular volume around the drill string directly above the first sealing device. 
     
     
         39 . The method as recited in  claim 37 , wherein, the drilling system further comprises:
 a fluid reservoir;   an injection pump configured to pump the fluid from the fluid reservoir into the annular volume around the drill string directly above the first sealing device, or, where the first sealing device and the second sealing device are provided, into the annular volume around the drill string between the first sealing device and the second sealing device; and   an injection line configured to connect the annular volume around the drill string directly above the first sealing device, or, where the first sealing device and the second sealing device are provided, the annular volume around the drill string between the first sealing device and the second sealing device, with the injection pump.   
     
     
         40 . The method as recited in  claim 39 , wherein the drilling system further comprises:
 a return line configured to connect the annular volume around the drill string directly above the first sealing device, or, where the first sealing device and the second sealing device are provided, the annular volume around the drill string between the first sealing device and the second sealing device, with the fluid reservoir; and   a back pressure valve arranged in the return line, the back pressure valve being configured to substantially restrict a flow of the fluid along the return line,   the method further comprising:   controlling the first fluid pressure in the annular volume around the drill string directly above the first sealing device, or, where the first sealing device and the second sealing device are provided, the annular volume around the drill string between the first sealing device and the second sealing device, by controlling the back pressure valve to vary an extent to which the back pressure valve restricts the flow of the fluid along the return line.   
     
     
         41 . The method as recited in  claim 40 , wherein the drilling system further comprises:
 a return pressure sensor configured to measure a return line fluid pressure in the return line, the return pressure sensor being arranged upstream of the back pressure valve.   
     
     
         42 . The method as recited in  claim 40 , wherein the drilling system further comprises:
 a back pressure valve arranged in the return line, the back pressure valve being configured to substantially restrict a flow of the fluid along the return line.   
     
     
         43 . The method as recited in  claim 42 , wherein,
 the drilling system further comprises a pressure sensor configured to measure a pressure, the pressure sensor being arranged in at least one of the injection line and the return line, and   the method further comprises:   using the pressure measured by the pressure sensor to control the first fluid pressure in the annular volume around the drill string directly above the first sealing device, or, where the first sealing device and the second sealing device are provided, using the pressure measured by the pressure sensor to control the annular volume around the drill string between the first sealing device and the second sealing device.   
     
     
         44 . The method as recited in  claim 40 , wherein the drilling system further comprises:
 an injection pressure sensor configured to measure an injection line fluid pressure in the injection line.   
     
     
         45 . The method as recited in  claim 40 , wherein the first sealing device, or, where the first sealing device and the second sealing device are provided, each of the first sealing device and the second sealing device, is configured to exert a sealing pressure which is variable on the drill string when operated to seal against the drill string. 
     
     
         46 . The method as recited in  claim 45 , wherein the method further comprises:
 varying the sealing pressure exerted by the first sealing device, or, where the first sealing device and the second sealing device are provided, varying the sealing pressure exerted by the first sealing device and the second sealing device, on the drill string to provide a leakage of an injected fluid between the respective sealing device and the drill string at a desired rate.   
     
     
         47 . The method as recited in  claim 46 , wherein the method further comprises:
 controlling the first fluid pressure in the annular volume around the drill string directly above the first sealing device by controlling the sealing pressure of the first sealing device, or, where the first sealing device and the second sealing device are provided, controlling the annular volume around the drill string between the first sealing device and the second sealing device by controlling the sealing pressure of each of the first sealing device and the second sealing device.   
     
     
         48 . The method as recited in  claim 40 , wherein the drilling system further comprises:
 a return line flow meter arranged in the return line upstream of the back pressure valve; and   an injection flow meter arranged in the injection line, and   the method further comprises:   monitoring an inflow rate of flow of the fluid into the annular volume around the drill string directly above the first sealing device, or, where the first sealing device and the second sealing device is provided, the annular volume around the drill string between the first sealing device and the second sealing device,   monitoring an outflow rate of flow of the fluid out of the annular volume around the drill string directly above the first sealing device, or, where the first sealing device and the second sealing device is provided, the annular volume around the drill string between the first sealing devices and the second sealing device;   comparing the inflow rate of flow and the outflow rate of flow, and   using the comparison to detect a loss of sealing integrity of the first sealing device, or, where the first sealing device and the second sealing device is provided, in at least one of the first sealing device and the second sealing device.   
     
     
         49 . The method as recited in  claim 48 , wherein the drilling system further comprises:
 a return pressure sensor configured to measure the fluid pressure in the return line,   wherein,   the injection flow meter and the return line flow meter are each a mass flow meter, and   the method further comprises:   comparing the inflow rate of flow and the outflow rate of flow, and   using the comparison to detect an influx of gas in the injected fluid.   
     
     
         50 . The method as recited in  claim 49 , wherein the drilling system further comprises:
 a mud gas separator, and   the method further comprises:   directing fluid from the return line to the mud gas separator if the influx of gas is detected in the injected fluid; and   returning a degasified liquid from the mud gas separator to the fluid reservoir.   
     
     
         51 . The method as recited in  claim 49 , wherein,
 the return line includes a main returns flow line which extends directly to the fluid reservoir, an emergency returns flow line which extends to the mud gas separator, and a valve assembly configured to control a flow of fluid along the main returns flow line and the emergency returns flow line, and   the method further comprises:   operating the valve assembly to close the main returns flow line and to open the emergency returns flow line if the influx of gas is detected in the injected fluid.   
     
     
         52 . The method as recited in  claim 39 , wherein,
 the drilling system is configured to automatically switch off the injection pump if the first fluid pressure in the annular volume around the drill string directly above the first sealing device, or, where the first sealing device and the second sealing device is provided, the annular volume around the drill string between the first sealing device and the second sealing device, exceeds a predetermined level.   
     
     
         53 . The method as recited in  claim 52 , wherein the method further comprises:
 adjusting the sealing pressure of the first sealing device to reduce the first fluid pressure in the annular volume around the drill string directly above the first sealing device, or, where the first sealing device and the second sealing device is provided, the annular volume around the drill string between the first sealing device and the second sealing device, to below the predetermined level.   
     
     
         54 . A tangible computer readable medium comprising instructions installed thereon which, when executed by a processing device, cause the processing device to perform a method of operating a drilling system for drilling a subterranean bore hole, the drilling system comprising:
 a drill string configured to rotate during a drilling; and   a sealing device configured to provide a substantially fluid tight seal around the drill string while the drill string is rotating during drilling,   the method comprising:   injecting a fluid into an annular volume around the drill string directly above the sealing device; and   controlling a first fluid pressure in the annular volume around the drill string above the first sealing device so that the first pressure is greater than a second fluid pressure in the annular volume around the drill string directly below the first sealing device.   
     
     
         55 . The tangible computer readable medium as recited in claim  33 , wherein the method further comprises:
 varying a sealing pressure exerted by the sealing device on the drill string to establish a leakage of the fluid between the sealing device and the drill string at a desired rate.