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Journal of Australian Energy Producers
RESEARCH ARTICLE (Non peer reviewed)

Applying Rate Transient Analysis (RTA) to integrate geological and engineering data

Nicholas Kwok A and Eamonn Montague A
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Santos Ltd.

The APPEA Journal 53(2) 473-473 https://doi.org/10.1071/AJ12084
Published: 2013

Abstract

The Blasingame typecurve in Fekete’s Rate Transient Analysis (RTA) software has been used at Santos to increase the understanding and integration of well and reservoir data; however, the authors have discovered that in some cases the tool produced anomalous results, such as permeability being too low. The potential consequence of this was incorrectly writing off reserves or making projects (in particular compression projects) fail economic tests.

After testing various hypotheses, a simple yet unorthodox solution was only discovered in a field where the anomaly was more profound, and required integrating geology and geophysics to explain it. This solution has since been applied in RTA models across numerous other fields, and it has improved the quality and confidence of these models.

The solution was the realisation that in many cases the accessed gas in place (GIP) increased over time, but the underlying model in RTA assumes a single tank, linear P/z. Matching the RTA model with the initial reservoir pressure and final accessed GIP results in over-predicting the reservoir pressures, resulting in an artificially low permeability. The authors discovered that the appropriate well and reservoir parameters could be obtained by matching the late time data using a lower initial reservoir pressure value corresponding to when the well had accessed the final GIP volume but not the initial reservoir pressure. This step was initially regarded to be counter-intuitive as the initial pressure is a measured property. Numerous reviews have endorsed this methodology, which is now being used as a standard at Santos.

Nicholas Kwok graduated from the University of Adelaide in 2010 with degrees in chemical engineering and finance. In 2011, he joined Santos in gas development as a graduate reservoir engineer. He was the compression focal point for the department, who provided reservoir engineering support for various compression projects across the Cooper Basin. He also has experience in various reservoir engineering analytical techniques, such as decline curve/rate transient analysis, pressure transient analysis, and GAP modelling. He is now working as a graduate-process control engineer as part of the Santos graduate program rotations.

Eamonn Montague graduated with a BSc (hons) (petroleum geology) in 1989. Afterwards, he became a graduate reservoir engineering at Santos. Since then, he has worked for 22 years as a reservoir/petroleum engineer in numerous countries, including four years as a lecturer/researcher at Australia’s Curtin University. He is now an asset lead in the gas development department at Santos, Adelaide.


References

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