Geothermal energy from the Main Karoo Basin? New insights from borehole KWV-1 (Eastern Cape, South Africa)

Abstract

Deep sedimentary basins are currently being assessed globally with respect to their geothermal energy resources. So far, the utilization of deep geothermal energy has not been addressed or included in any renewable energy scheme of South Africa. However, the Main Karoo Basin, with an area of 700,000 km2 and a basin fill of more than 5000 m of siliciclastic rocks, is a promising target for future enhanced geothermal system (EGS) resource exploration, development and production. Here, we present petro- and thermophysical data from a deep borehole (KWV-1), drilled in 2015 within the framework of the research programme KARIN (Karoo Research Initiative) near the town Willowvale in the Eastern Cape Province. The borehole intersected a 1375 m thick siliciclastic succession of the Permian Ripon Formation up to 2276 m depth. Dolerite sills are characteristic features of the succession, dividing the sedimentary series. The clastic rocks show low matrix permeabilities and high thermal conductivities ranging from 3.17 to 3.71 W/(m·K). Specific heat capacity is highest in siltstones and fine-grained sandstones. Reservoir permeability may be enhanced by joint and fracture systems and dolerite sills with potential for fluid-flow channelling along the intrusion-host rock interfaces. Temperatures of 80 °C at 2200 m depth indicate a moderately elevated geothermal gradient. Sandstones of the Ripon Formation occurring at >3000 m depths in the southern Eastern Cape region are promising EGS reservoirs with temperatures >100 °C suitable for electricity production in a binary geothermal power plant.