Kick detection during drilling

Abstract

Gas influx into a wellbore, called A 'kick', is detected by two different, yet complementary methods during active drilling of the borehole. The first method is based upon the existence of standing wave patterns generated by pressure oscillations of the drilling rig mud pumps. Such standing wave patterns form time sequences of maximum and minima as a gas slug moves upwardly in the annulus. The time between such peaks of such oscillations is measured and forms the basis for generation of one first kick signal. A continuous increase in the phase between annulus and drill string standing waves forms the basis for another standing wave kick signal. The second method uses acoustic signals from a downhole source near the bottom of the borehole which are transmitted at different speeds in the annulus mud and in the interior drill string mud, where the annulus mud may be gas cut. A difference in arrival time between the signals is determined, and if large enough, causes a second kick signal to be generated. A third method may be used where at least two drilling pumps are used in the drilling system. Such method determines the total travel time, from standpipe to drill string and up the annulus, of a beat frequency pressure wave caused by slightly different frequencies of the two pumps. An alarm signal is generated if the total travel time is greater than a computed threshold.