Gas-Influx Detection With MWD Technology

Abstract

This paper describes a new gas-influx detection technique that monitors the acoustic responses of annular measurementwhile-drilling (MWD) pulses to provide a rapid, early warning of the development of potential gas-kick situations. The technique has been evaluated in both water-and oil-based muds during about 40 gas-kick simulations at two full-scale testing facilities. Free gas is identified by amplitude attenuation and phase delay of MWD fundamentals and their harmonic frequencies. Detection is independent of influx location because the entire length of the annulus between the bit nozzles and a surface-pressure transducer is sampled. Detection of potential gas-kick situations generally occurred within minutes of influx initiation, before any significant gas expansion.Some tests also evaluated a downhole MWD mud-resistivity sensor. Results indicated that both these techniques, and particularly the pulse acoustics, can provide unequivocal confirmation of gas and an earlier warning of gas-kick situations than conventional kickdetection techniques.

Kick Detection at the Bit: Early Detection via Low Cost Monitoring

“…Based on those rules, a model of the expected signal response was built with respect to depth, for influx and non-influx conditions, taking into consideration the various physical parameters that affect the resistivity log so that a difference in response would indicate influx. Bryant et al (1991) tested a formation fluid influx detection technique which monitors electrical resistivity and acoustic responses of annular MWD measurements. Gas was the primary formation fluid tested in the experiments, but both freshwater and salt water were also tested.…”

Improve Drilling Safety and Efficiency With MWD Sensors

“…The mud resistivity sensor simply employs a small resistivity probe on the drill collar to detect any change of mud resistivity due to migration of hydrocarbons or water [15]. The annular acoustic response technique analyzes the changes of pressure wave characteristics in the annulus to determine the presence of gas in the well bore [15].…”

“…The most recent paper by Bryant, Grasso, and Wallace [15] presents detail test results of a mud resistivity sensor and the annular acoustic response technique. The two techniques reported to have detection sensitivity in the order of 0.5 to 1.0 bbl/min.…”

“…Figure 6 shows detection time at various influx rates for three detection methods [15,20]. All three methods can signal an alarm within 1.5 minutes ifthe influx rate is more than 1.0 bbl/min.…”

Acoustic Gas Kick Detection With Wellhead Sonar

“…The response time of these measurements may be too long under certain situations. In contrast, acoustic kick detection systems have the potential of detecting the gas downhoIe, and in the earliest stages of a kick [3,4,5]. A common feature of the present day acoustic systems is that they rely on pressure generated during mud circulation.…”