Method for Gas Zone Detection Using Sonic Wave Attributes

Abstract

A method for determining on a real time logging while drilling (LWD) basis gas within earth formations traversed by a borehole. Continuous LWD acoustic measurements are recorded and processed including coherent energy and attenuation attributes to detect downhole gas zones and kick during drilling operations.

What is claimed is: 
     
         1 . A method for determining the presence of a formation gas kick on a real time basis by a logging while drilling process comprising:
 emitting periodic sonic wave energy toward a borehole formation by a logging while drilling tool;   receiving Stoneley waveform signals transmitted within the borehole;   determining the lithology of formations as drilling progresses;   determining the Stoneley wave slowness (DTst) within the well bore; and   for an essentially uniform formation lithology determining the presence of gas kick within the borehole by a sudden change at different depths in Stoneley slowness (DTst) over formations with essentially similar lithology.   
     
     
         2 . A method for determining the presence of a formation gas kick on a real time basis by a logging while drilling process as defined in  claim 1  and further comprising:
 determining the Stoneley wave attenuation (ATTst) within the well bore; and 
 for an essentially uniform formation lithology confirming the presence of a gas kick within the borehole by a sudden increase in Stoneley attenuation (ATTst). 
 
     
     
         3 . A method for determining the presence of formation gas kick on a real time basis by a logging while drilling process as defined in  claim 1  and further setting as gas kick flag comprising:
 detecting a change in the Stoneley slowness (DTst); and 
 setting a kick flag to warn a driller of the drilling operation encountering a formation gas kick in the event the detected change in (DTst) exceeds a set value. 
 
     
     
         4 . A method for determining the presence of a formation gas kick on a real time basis by a logging while drilling process as defined in  claim 1  and further comprising:
 determining the Stoneley wave coherent energy (CEst) within the well bore; and 
 for an essentially uniform formation lithology confirming the presence of a gas kick within the borehole by a sudden decrease in Stoneley coherent energy (CEst). 
 
     
     
         5 . A method for determining the presence of a formation gas kick on a real time basis by a logging while drilling process as defined in  claim 4  and further comprising:
 detecting a change in one or more Stoneley attributes of (DTst, ATTst and CEst) and prior to setting a kick detection flag assigning a weighting factor to one or more of the Stoneley attributes (DTst, ATTst and CEst). 
 
     
     
         6 . A method for determining the presence of a formation gas kick on a real time basis by a logging while drilling process comprising:
 emitting periodic sonic wave energy toward a borehole formation by a logging while drilling tool;   receiving Stoneley waveform signals transmitted within the borehole;   determining the lithology of formations as drilling progresses;   determining the Stoneley wave attenuation (ATTst) within the well bore from the attributes of received coherent Stoneley waveform signal peaks; and   for an essentially uniform formation lithology determining the presence of gas kick within the borehole by a sudden change at different depths in Stoneley wave attenuation (ATTst) over formations with essentially similar lithology.   
     
     
         7 . A method for determining the presence of a formation gas kick on a real time basis by a logging while drilling process as defined in  claim 6  and further comprising:
 determining the Stoneley wave coherent energy (CEst) within the well bore; and 
 for an essentially uniform formation lithology confirming the presence of a gas kick within the borehole by a sudden decrease in Stoneley coherent energy (CEst). 
 
     
     
         8 . A method for determining the presence of formation gas kick on a real time basis by a logging while drilling process as defined in  claim 6  and further setting as gas kick flag comprising:
 detecting a change in the Stoneley attenuation (ATTst); and 
 setting a kick flag to warn a driller of the drilling operation encountering a formation gas kick in the event the detected change in (ATTst) exceeds a set value. 
 
     
     
         9 . A method for determining the presence of a formation gas kick on a real time basis by a logging while drilling process comprising:
 emitting periodic sonic wave energy toward a borehole formation by a logging while drilling tool;   receiving Stoneley waveform signals transmitted within the borehole;   determining the lithology of formations as drilling progresses;   determining the Stoneley wave coherent energy (CEst) within the well bore; and   for an essentially uniform formation lithology determining the presence of gas kick within the borehole by a sudden change in Stoneley coherent energy (CEst) over formations with essentially similar lithology.   
     
     
         10 . A method for determining the presence of formation gas kick on a real time basis by a logging while drilling process as defined in  claim 9  and further setting as gas kick flag comprising:
 detecting a change in the Stoneley coherent energy (CEst); and 
 setting a kick flag to warn a driller of the drilling operation encountering a formation gas kick in the event the detected change in (CEst) exceeds a set value.