Patent ID: 8547789

Claim:
A method for determining the presence of a formation gas zone during a well logging operation by monitoring sonic waveform signals for coherent arrivals comprising: emitting periodic sonic wave energy toward a borehole formation by a well logging system in a borehole; receiving compressional wave signals refracted from the formation from said periodically emitted sonic waves; receiving shear wave signals refracted from the formation from said periodically emitted sonic waves; determining compressional slowness (DTc) from attributes of received coherent compression signal peaks; determining shear slowness (DTs) from attributes of received coherent shear signal peaks; determining a compressional wave attenuation attribute (ATTc); determining a shear wave attenuation attribute (ATTs); determining a compressional wave coherent energy attribute (CEc); determining a shear wave coherent energy attribute (CEs); detecting zones of rock formation containing gas in logging while drilling time using combinations of logging while drilling sonic attributes DTc/DTs, ATTc/ATTs, and CEc/CEs to form a gas zone flag; and detecting presence of gas in the borehole in logging while drilling time using combinations of logging while drilling sonic attributes of borehole Stoneley waves DTst, ATTst, and CEst to form a gas kick flag.