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.
Highlights
Within the global scenario of renewable energy exploitation, geothermal energy has undergone an enormous increase in recent years
Campbell et al (2016a) provided a first estimation of the geothermal power generation potential of the Karoo Basin based on petro- and thermophysical data from an outcrop study of Permian sandstones in the Eastern Cape Province, and evaluation of groundwater temperature data and heat flow values from literature
The studied borehole KWV-1 was drilled in an abandoned quarry 10 km E of the town Willowvale (Fig. 1) in the Eastern Cape Province, South Africa (32°14′43.10′′ S, 28°35′08.10′′ E; 263 m a.s.l.) within the framework of the research programme KARIN (Karoo Research Initiative) and represents the first deep Karoo borehole since the SOEKOR exploration drilling program undertaken in the 1960s and 1970s
Summary
Within the global scenario of renewable energy exploitation, geothermal energy has undergone an enormous increase in recent years. Besides high-enthalpy volcanic settings (e.g., Chambefort and Bignall 2016), deep sedimentary basins are currently being assessed globally with respect to their geothermal energy resources (e.g., Eggeling et al 2011; Zafar and Cutright 2014; Horváth et al 2015; Lenhardt and Götz 2015; Zhu et al 2015). The utilization of deep geothermal energy has not been addressed or included in any renewable energy scheme of South Africa. Campbell et al (2016a) provided a first estimation of the geothermal power generation potential of the Karoo Basin based on petro- and thermophysical data from an outcrop study of Permian sandstones in the Eastern Cape Province, and evaluation of groundwater temperature data and heat flow values from literature. A volumetric approach of the sandstones’ reservoir potential led to a first estimation of 2240 TWh (8.0 EJ) of power generation potential within the central and southern parts of the basin
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