Patent ID: 8794062

Claim:
An apparatus configured to detect a gas influx in a borehole fluid during drilling operations, the apparatus comprising: a bottomhole assembly (BHA) configured to be conveyed in the borehole filled with the borehole fluid; a transducer assembly on the outside of the BHA including a transducer configured to be in contact with the borehole fluid in an annulus between the BHA and a wall of the borehole while the BHA is submerged in the borehole fluid and configured to generate an acoustic pulse in the borehole fluid; a stepped reflector on the transducer assembly configured to be positioned in the annulus in contact with the borehole fluid while the BHA is submerged in the borehole fluid and configured to produce at least two reflections of the acoustic pulse; and a processor configured to use a response of the transducer to the at least two reflections to provide an indication of the gas influx; wherein the response of the transducer comprises a signal including a first signal arrival and a second signal arrival corresponding to the at least two reflections, and wherein the processor is further configured to: (i) estimate from the signal an acoustic velocity of borehole fluid, and (ii) use the estimated acoustic velocity to provide an indication of the gas influx.