Method and system for identifying a self-sustained influx of formation fluids into a wellbore

Abstract

A method of identifying a self-sustained influx of formation fluids into a wellbore includes the steps of closing an annular shut-off device and diverting an annular return flow from the wellbore through a first flow rate measurement device, measuring a flow rate of said annular return flow, measuring an inlet flow rate of fluids entering the well through a second flow rate measurement device in a fluid injection line, and identifying a self-sustained influx of formation fluids if a non-decreasing measured annular return flow rate is greater than said measured inlet flow rate.

1 . A method of identifying a self-sustained influx of formation fluids into a wellbore ( 12 ) being drilled in a formation ( 14 ), the method comprising the steps of:
 closing an annular shut-off device ( 31 ) and diverting an annular return flow from the wellbore through a first flow rate measurement device ( 50 ,  58 );   measuring a flow rate of said annular return flow;   measuring an inlet flow rate of fluids entering the wellbore through a second flow rate measurement device ( 52 ) in a fluid injection line ( 48 ); and   upon determining that the measured annular return flow rate is greater than the measured inlet flow rate, identifying the presence of a self-sustained influx of formation fluids based upon a non-decreasing measured annular return flow rate.   
     
     
         2 . The method of  claim 1 , further comprising reducing said inlet flow rate, and, upon determining that the measured annular return flow rate is greater than the measured inlet flow rate, identifying the presence of a self-sustained influx of formation fluids based upon a non-decreasing measured annular return flow rate. 
     
     
         3 . The method of  claim 2 , further comprising the steps of:
 fully reducing said inlet flow rate to substantially zero, and, upon determining that the measured annular return flow rate is greater than the measured inlet flow rate, identifying the presence of a self-sustained influx of formation fluids based upon a non-decreasing measured annular return flow rate.   
     
     
         4 . The method of  claim 3 , further comprising the step of:
 ruling out the presence of a self-sustained influx of formation fluids at existing flow rates based upon a decreasing measured annular return flow rate.   
     
     
         5 . The method of  claim 1 , further comprising:
 generating a signal F out (t) representative of said annular return flow rate;   generating a signal F in (t) representative of said inlet flow rate; and   transmitting said signals F in (t) and F out (t) to a central control unit, which receives said signals F in (t) and F out (t) and computes a delta between said signals F in (t) and F out (t).   
     
     
         6 . The method of  claim 5 , further comprising the step of increasing back pressure on said annular return flow using a flow control device when a self-sustained influx is identified. 
     
     
         7 . The method of  claim 6 , further comprising the step of increasing back pressure on said annular return flow by an amount required to decrease said annular return flow indicated by signal F out (t) to substantially the same as said inlet flow rate indicated by signal F in (t). 
     
     
         8 . The method of  claim 7 , further comprising the step of automatically increasing back pressure on said annular return flow by said central control unit. 
     
     
         9 . The method of  claim 4 , further comprising the step of reopening the annular shut-off device after ruling out the presence of a self-sustained influx of formation fluids into the wellbore. 
     
     
         10 . The method of  claim 1 , further comprising the step of stopping rotation of a drillstring ( 20 ) or lifting said drillstring off a well bottom. 
     
     
         11 . A method of identifying or ruling out a self-sustained influx of formation fluids into a wellbore ( 12 ) being drilled in a formation ( 14 ), the method comprising the steps of:
 closing an annular shut-off device ( 31 ) and diverting an annular return flow from the wellbore through a first flow rate measurement device ( 50 ,  58 );   measuring a flow rate of said annular return flow;   measuring an inlet flow rate of fluids entering the wellbore through a second flow rate measurement device ( 52 ) in a fluid injection line ( 48 ); and   upon determining that the measured annular return flow rate is greater than the measured inlet flow rate, ruling out the presence of a self-sustained influx of formation fluids at existing flow rates based upon a decreasing measured annular return flow rate.   
     
     
         12 . The method of  claim 11 , further comprising ruling out the presence of a self-sustained influx of formation fluids based upon the measured annular return flow rate decreasing to substantially zero.