For the first time, the technique of gas chromatography - mass spectrometry (GCMS) has been adapted for and tested at the well site. Product of a GEOSERVICES research program, this equipment is designed to record the measurement of hydrocarbon gases and vapors from C1 to C8, including BTX (Benzene-Toluene-Xylenes), non-hydrocarbon and sour gases. The GCMS tool on its own would not have been sufficient to record all these parameters; another major technical difficulty concemed the extraction of all these components from the mud, and their transport to the mud logging unit for analysis. This was solved using a new generation, heated gas trap and associated specific gas line, resulting from research carried out by GEOSERVICES and IFP (French Institute of Petroleum). The GCMS tool was tested for basic functioning on a well in Indonesia in 2000. The complete system was installed for a full test on a deep offshore well in late 2001. The project had two main objectives: To provide the detection of new components (C6 to C8), previously unmeasured at the well site, while also enabling the precise identification of non-hydrocarbon and sour gases (e.g. CO2). To provide high quality, high resolution gas data with better heavy component detection in low temperature muds (deep offshore), greater component detection sensitivity and higher vertical resolution due to faster gas component identification. The principal impact of the project concems gas data interpretation such as the accurate location of transition zones, fluid differentiation, reservoir quality layering etc. The availability of these new data will permit: - An early evaluation of the formation and fluids encountered, with better quality thanks to the identification of the heavier components. - Efficient real-time decisions concerning the optimization of the subsequent well program (well trajectory, coting, data acquisition, formation testing) and its cost.

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