The probe’s performance is unaffected by mud type, temperature, or flow rate.

Weatherford’s GC-TRACER surface gas detector lends increased relevance to the role of formation gas analysis in reservoir evaluation during drilling operations. While such analysis has been used as a reservoir evaluation tool for decades, traditional extraction techniques have limited its applicability. Leveraging a patented membrane-based extraction method, the GC-TRACER surface gas detector delivers more accurate, timely results. Ratio analysis of gas extracted directly from drilling fluid enables operators to evaluate hydrocarbon reservoirs with unprecedented precision and, as a result, to make more cost-effective drilling and completion decisions.

The GC-TRACER surface gas detector uses an innovative extraction method to minimize sampling errors. Housing a semi-permeable membrane, its slim probe is inserted into the flowline to extract gases. The probe’s performance is unaffected by mud type, temperature, or flow rate. Furthermore, its lack of moving parts eliminates risk of mechanical failure, another drawback of the gas trap. Exploiting differences in the individual partial pressure of gases between the probe and the drilling fluid, the membrane allows permeation of hydrocarbon and non-hydrocarbon gases, free or dissolved.

A helium carrier gas transports extracted hydrocarbons to a micro-gas chromatograph (GC) while helping maintain partial pressure differential. Heated sample lines prevent condensation, ensuring more representative samples and improved system response. The closed-flow system prevents air dilution of samples, likewise contributing to more accurate results.

A North Sea operator used the gas detector to evaluate a reservoir associated with a discovery well and to select coring points for the well’s three sidetracks. The gas detector proved instrumental in evaluating the reservoir and in helping to confirm well-to-well correlations.

When the discovery well was drilled mid-2007, the GC-TRACER surface gas detector provided a gas character/fingerprint of the reservoir, upon which future sidetracks could be optimized. It provided a detailed picture of the vertical character of the reservoir, which helped to identify comparatively thin beds with the highest potential for production.

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