An integrated approach of fluid contact determination of the Albian age sandstone reservoirs of the Orange Basin Offshore South Africa

Abstract

The Orange Basin situated offshore South Africa has been subject to various studies as it is gas prone, but limited literature exists on the determination of fluid contacts. The availability of well logs, repeat formation tests (RFT), and drill stem test (DST) results make the Orange Basin an ideal example to carry out studies on the integration of these data to understand the fluid contacts in the Albian age gas bearing sandstone reservoirs. This paper compared pressure gradient results from repeat formation test, drill stem analysis, and well logs in the Orange Basin Offshore in South Africa, for the identification of fluid types and contacts in the Albian age sandstone reservoirs. In most of the wells, the interpreted water pressure gradient ranges from 0.42 to 0.45 psi/ft (0.98 to 1.04 g/cm³ equivalent). Results reveal the field water pressure gradient of 0.43 psi/ft (1.01 g/cm³). The combination of pressure data helps to improve the interpretation of conventional log data and provide useful information on the prediction of fluid contacts, as demonstrated in this study. Findings from this study provide insights during the phases of petroleum exploration and development to understand pressures that would improve drilling safety. Additionally, previously unclear fluid contacts from well logs are revealed and easily predicted with a better understanding of connectivity and isolation of reservoirs.

Keywords:

• Repeat formation tester
• fluid contact
• sandstone reservoir
• pressure gradient
• Orange Basin

Acknowledgements

The author wishes to thank the Petroleum Oil and Gas Company of South Africa (PetroSA) for funding the research work and the Petroleum Agency of South Africa (PASA) for the provision of the dataset. Thanks go to LR Senergy for the provision of the Interactive Petrophysics™ (IP) log interpretation software. Appreciation to these mentors of this study, Mrs Florangel Poquioma, Professor Paul Carey, and Mr Jeff Aldrich, for their valuable support. Thanks to the editor and reviewer of this work.

Disclosure statement

The author declares that no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.