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2018 AAPG International Conference and Exhibition

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Assessing the Shale Gas Potential of the Southern Main Karoo Basin, South Africa

Abstract

In South Africa, the Whitehill Formation is considered the most prospective target for shale gas exploration, owing to its favourable maturities, total organic content (TOC), mineralogical content, lateral expanse and depth. This study focuses on the assessment of the shale gas potential of South Africa and addresses the limitations in the evaluation of the Karoo Basin shales. The resource was evaluated using 1D basin modelling, interpretation of 2D seismic, well data, remote sensing and published literature. These analyses were then combined to produce common risk segment maps to evaluate the resource potential of the shales within the main Karoo basin of South Africa. 1D basin modelling was performed on four wells specifically; KL1/65, KW1/67, SA1/66 and SP1/69. Three basal heat flows (transient, steady state and rifting) were used to simulate the models for each well. The aim of the basin modelling exercise was to ascertain the generative ability of the Karoo rocks to generate hydrocarbons. Interpretation of the 2D seismic data revealed southward-dipping faults and deformation along the southern margin of the Karoo basin and Cape Fold belt. In addition, no deformation was observed within the Namaqua-Natal basement. The four reflectors (Bokkeveld Group, Table Mountain Group, Whitehill Formation and Namaqua-Natal basement) were stratigraphically mapped and gridded. Finally, the gridded Whitehill reflector was depth converted to create the top of the Whitehill Formation depth map. The 2D seismic, 1D basin modelling and relevant literature were incorporated into the development of common risk segment maps that were used to delineate the prospective area for shale gas. Evaluation of Karoo shales within South Africa are still within the resource phase, in that the existence of significant movable hydrocarbons need to be established. This will require a well to be drilled to test the commercial viability of the shales. Until this has been done the resource estimates are speculative, nonetheless geological considerations and the available data can be used to inform decisions and guide future research.