Using mud gas components to quantify hydrocarbon liquid yields for gas zones in the Patchawarra Formation of the Western Flank, Cooper Basin

The Patchawarra Formation is a Permian age fluvial sand and coal measure system deposited in the Cooper Basin of Central Australia. Fluvial sand channels up to 20 m thick form conventional gas reservoirs and are inter-bedded with seal and hydrocarbon source play components of overbank silts, clays and coal seams. This stacked play system presents a challenge to completion optimization and efficiency, which are critical components for achieving an economic well. A key driver to the success and economics of a well is the presence of liquid hydrocarbons (LPG; Propane and Butane and condensate; Pentane plus). As the liquid yields composition varies significantly throughout the Cooper Basin, estimating the liquid yield in new gas zones is vital to valuations of any potentially commercial development in this area. This paper will present a new quantifiable method to forecast the liquid yields of specific gas zones utilizing mud gas logs. The method uses simple formulas applied to mud gas ratios to provide estimates of liquid yield per individual gas zone. Examples demonstrate the application of the method, calibration of fluid estimates to real PVT samples from corresponding gas zones and how the results have successfully optimized completion strategies in the Beach Energy operated Western Flank gas area. It is anticipated that with continued application, this simple method will become a useful tool in assessing the commerciality of gas wells and assist in identifying future exploration/appraisal and development targets.