Advances in Chromatographic Analysis of Hydrocarbon Gases in Drilling Fluids ? The Application of Semi-Permeable Membrane Technology to High Speed TCD Gas Chromatography

The rapid analysis of hydrocarbon gases present in drilling fluids has the potential to bring about significant benefits in terms of drilling efficiencies, whether through reliable determination of fluid contacts or as a geo-steering tool. However, it is only with recent advances in gas detection technology that the true worth of such analysis can be fully utilised. The application of mud gas analysis to reservoir characterisation and formation evaluation has long been hampered by poor gas extraction techniques and Chromatographs providing limited temporal and spectral resolution. In order to improve detection capabilities, researchers have looked to developing rather than avoiding the weak link in the gas extraction/analysis chain ? the gas trap. Yet it?s use still precludes the evaluation of actual gas in mud, due to the recurring problems of gas trap loading, the variability in efficiency according to mud type and the sampling of ambient gases, providing analysis of gas in air rather than gas in mud. Where such issues have been minimised, the divorcing of the point of extraction from the point of analysis and the subsequent lag times which are incurred, create further problems in terms of real-time capabilities. This paper details the combination of two techniques, which have been developed to enhance the accuracy, repeatability and resolution of gas detection at wellsite. The result of this development is a tool, which provides a full chromatographic breakdown of free and dissolved Hydrocarbon gases from Methane (C1 to Octane (C8, along with aromatics (Benzene & Toluene, sour gases (H2S & CO2 and Nitrogen. The system provides a direct gas in mud analysis at the point of extraction, by utilising a semi-permeable membrane probe, coupled with the latest in high-speed TCD Chromatography. The extraction of hydrocarbon gases through a gas permeable membrane was first developed by Brumboiu et al, 2000. Whilst it?s application at the time was limited to total gas detection, it has proven that the principle is both reliable and rugged enough for wellsite deployment. Experimental and field data show the potential of the tool in fast, heavy gas spectrum analysis with the accompanying benefits of improved fluid contact determination, reservoir characterisation and geo-steering. With excellent separation of all component peaks and elution times, which bring full analysis, incorporating C1-C8, aromatics and non-hydrocarbon gases, within 50seconds. This combination of membrane technology and TCD chromatography presents a significant advance in the real-time characterisation of hydrocarbon bearing zones.