Acoustic Gas Kick Detection With Wellhead Sonar

Abstract

Abstract An acoustic gas kick detection system has been successfully tested in full-scale experiments. The principle of operation is similar to that of an echo-sounder system. The method is neither dependent on mud circulation, nor does it require the presence of the drillpipe. It can be applied to both platforms and floating rigs. Furthermore, only surface equipment is required for its operation. In the experiments 150 to 600 l of gas was injected at a depth of 1210 m both in water and in water-based drilling fluid. The results show that the changes caused by the presence of free gas in the well are easily and instantly detected. Introduction The influx of hydrocarbon gas into the borehole while drilling represents a serious hazard. If such a gaskick is not handled properly, a blowout of the well may be the ultimate consequence. With the advent of slimhole and high temperature/high pressure drilling, the detection of potential gaskicks is of increasing importance. Kick detection systems in common use include pit gain or differential flow measurements. 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 downhole, and in the earliest stages of a kick. A common feature of the present day acoustic systems is that they rely on pressure generated during mud circulation. This implies that they do not function during, e.g., tripping, which is a drilling phase in which kicks more easily occur because of the reduced pressure balance and the swabbing effect of the drillstring. Statistics show that as many blowouts occur while tripping out as occur while drilling. Presently, no acoustic system is available that functions irrespective of whether mud is circulated. This paper describes the investigation of a concept to detect gas kicks, termed the "wellhead sonar", that does not require mud circulation. Furthermore, no downhole equipment is needed and the system functions with and without the drill string in the hole. P. 249^