Publications

Analysis of hydrocarbons extracted from drilling mud is now a routine procedure during drilling operations, mainly because of safety reasons. It is an integral part of the services provided by mudlogging contractors. The aim of gas analysis in the earliest days of mudlogging was mainly for recognition of formation fluids, but improvements in electric logs combined with the uncertainty of gas measurements led to more emphasis on safety aspects. The introduction of efficient gas extraction systems and capillary gas chromatograms resulted in revival of using mud gas data for early recognition of hydrocarbon-bearing formations. Modern systems with a flame ionization detector can analyze gas samples for C1 to C5 hydrocarbons in less than 6 minutes. Enthusiasm for this application, however, has been tempered by advancements in logging while drilling (LWD) devices together with remaining uncertainties of gas measurements. Moreover, the limited vertical resolution of one analysis every 6minutes poses an additional problem as drilling rates of penetration progressively increase and exploration objectives commonly focus on thin-layered, stacked reservoirs. Analyzing only C1 to C3, gases overcomes part of the problem, although some information is lost. Alternatively, this paper presents the first results of a newly developed gas analyzer with a cycle time less than 45 seconds for the analysis of C1 to C5 hydrocarbons. Examples from the Gulf of Thailand and the Andaman Sea show that, despite the uncertainties inherent to the analysis of mudlogging gas data, important information can be retrieved regarding formation fluids as well as the recognition of overpressured zones.