Geochemistry and organic petrology of the permian whitehill formation, Karoo Basin (RSA) and the Devonian/Carboniferous shale of the Appalachian Basin (USA)

Abstract

Globally, there is significant economic interest in shale gas as a hydrocarbon resource. The success of unconventional shale gas exploration in the United State of America (USA) has raised interests for potential shale gas development in the Karoo Basin of South Africa. The Karoo Basin technically recoverable shale gas resource is estimated to be 13 Tcf, with 19–23 Tcf recoverable free gas. Due to the potential importance of the South African resource, this study characterized the Lower Permian Ecca Group shale and compared its geochemical and organic petrology properties with those of Devonian/Carboniferous shales of the Appalachian Basin, USA. The comparison of research data will aid in the understanding of shale gas potential of the Karoo Basin. Horizons from two boreholes (KZF-01 and KWV-01) drilled in the southern and southeastern Karoo Basin were evaluated and compared with samples of the Late Devonian Ohio and Early Carboniferous Sunbury Shales from the central Appalachian Basin, USA. Total organic carbon (TOC), total sulphur (TS), and organic petrology (bitumen and vitrinite reflectance, and maceral analysis) were used to assess organic richness and thermal maturity of the shale samples. In addition, the samples were evaluated for mineralogical content using X-Ray Diffraction (XRD). Data indicates that the Whitehill Formation of the Karoo Basin has good to excellent shale source potential, with an average TOC of 4.35 wt%. However, thermal maturity data of the Whitehill Formation shows the organic matter to be overmature, with vitrinite reflectance equivalent values greater than 3% RoV. Total sulphur data for the Whitehill Formation and the Devonian/Carboniferous shales suggests that both were influenced by marine environments. Both the KWV-01 and Ohio/Sunbury shale samples contain high amounts of quartz, with clay mineral contents greater than 40% being observed in borehole KWV-01 samples. Collectively, this research study provides valuable data for shale gas exploration and development in the Karoo Basin, South Africa.