Method of monitoring gas influx into a well bore when drilling an oil and gas well, and apparatus constructed in accordance with the method

Abstract

A method of monitoring gas influx into a well bore when drilling an oil and gas well. A first step involves positioning a pressure sensor in a well bore at a lower end of a well casing string. A second step involves connecting the pressure sensor to a pressure reader and monitoring the pressure reader for pressure changes indicative of gas influx.

1 . A method of monitoring gas influx into a well bore when drilling an oil and gas well, comprising the steps of: 
 positioning a pressure sensor in a well bore at a lower end of a well casing string; and    connecting the pressure sensor to a pressure reader and monitoring the pressure reader for pressure changes indicative of gas influx.    
   
   
       2 . The method as defined in  claim 1 , the pressure sensor being positioned in the well bore by incorporating the pressure sensor into a cavity in tubular members making up the lower end of the well casing string.  
   
   
       3 . The method as defined in  claim 2 , the pressure sensor being positioned within a float collar at the lower end of the well casing string.  
   
   
       4 . The method as defined in  claim 3 , a fluid communication port being provided through the float collar to the cavity to allow fluids in the well bore to communicate with the cavity in which the pressure sensor is positioned.  
   
   
       5 . The method as defined in  claim 4 , the fluid communication port having a protective closure which closes the fluid communication during cementing, the protective closure being removed after cementing.  
   
   
       6 . (canceled)  
   
   
       6 . (canceled)  
   
   
       7 . An apparatus for monitoring gas influx into a well bore, comprising: 
 a tubular body having defining side walls with an interior surface and an exterior surface,    a pressure sensor being positioned within a cavity formed in the side walls;    a passage extending from the interior surface into the body to provide fluid communication with the cavity; and    means for communicating pressure sensor readings from the pressure sensor to a pressure reader positioned on surface.    
   
   
       8 . The apparatus as defined in  claim 7 , wherein the tubular body is a float collar.