A case study of sandstone reservoir characterization of wells in the Orange Basin, offshore South Africa

Abstract

This study used seismic and petrophysics data to identify potential subsurface facies that are viable hydrocarbon productive areas in the southern part of the Orange basin of South Africa. Two target areas were identified as target areas 1 and 2. In Target Area 1, three facies were identified: sand, silt and shale. The sand facies has the best reservoir quality (volume of shale between 20 to 30%; porosity from 9 to 17%; permeability from 5 to 15 mD, and water saturation from 40 to 60%), while the shale facies present the lowest reservoir quality rock (volume of shale greater than 40%; porosity from 0 to 5%; permeability from 0 to 0.5 mD, and water saturation from 80 to 100%). Target Area 1 mainly consisted of silty shale and shaly silt. However, Target Area 2 had the same facies as Target Area 1, except with additional basement facies comprising well-sorted fine to medium-grain sands. Target Area 2 had considerably thicker sand layers; thus, the petrophysical properties are slightly better, with the basement facies having a volume of shale less than 20%, porosity between 20 and 23%, permeability greater than 15mD, and water saturation between 30 and 45%. The overall reservoir rock quality in the triangulated area is generally poor because of a high concentration of clay in the matrix in sandstone layers. Regarding economic potential, Target Area 2 was identified as the most productive area with better reservoir qualities due to the basement facies. The recoverable gas in Target Area 1 is 95 057 cubic metres, while area 2 has a volume of 151 923 cubic metres. This study has shown for the first time that the southern part of the Orange Basin is not economically viable.

Keywords:

• Orange basin
• reservoir characterization
• target areas
• petrophysical properties
• seismic

Acknowledgements

The authors thank the Petroleum Company of South Africa (PetroSA) and the Petroleum Agency of South Africa (PASA) for providing the data sets used in this study and the permission to publish the results. We also acknowledge Schlumberger’s support for using the Petrel Software package. Additionally, our thanks also go to Synergy Company for the provision of the Interactive Petrophysics package.

Disclosure statement

No potential conflict of interest was reported by the authors.

Ethical clearance

The research does not require any ethical clearance issues.