Browsing by Author "Martin, Jonathan William"
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- ItemExploration into the potential for a low-enthalpy geothermal power plant in the Cape Fold Belt(Stellenbosch : Stellenbosch University, 2020-03) Martin, Jonathan William; Croukamp, Leon; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: South Africa has long been dependent on coal and other fossil fuels for cheap electricity generation. While there has been an increase in utilising renewable energy over the last two decades, the main focus has been on solar and wind, while geothermal energy is not considered by the main power producer Eskom or private energy producers and only limited research has been done by academics. With advances in technology that harness geothermal energy from a wider range of temperatures, geothermal resources as low as 85oC have been reported attainable when using low-enthalpy technologies as such binary systems. This makes geothermal energy a reality for regions in South Africa where moderately high geothermal gradients exist; making sure the geothermal gradient is high enough to obtain necessary heat energy from 3-4km depth. The initial high level assessment of the geothermal potential of the Cape Fold Belt region was done through accessing seven hot springs found to have the highest temperature from previous studies. Temperature measurements, amongst other parameters, were taken as close to the source as possible as well as collection of water samples for ICP-AES analysis for major cations. The cation concentrations from the ICP-AES analysis allowed for geothermometry calculations to be conducted which gave the minimum temperature estimates of the reservoirs of each hot spring. Both the surface temperature measurements and the estimates of the reservoir temperature resulted in two locations that were in the top three for both measurements. These two locations were Calitzdorp and Caledon, having surface measurements of 47oC and 45oC and estimates of the reservoir temperatures of 117oC ±13oC and 108oC ±21oC respectively. The analysis of the Oudtshoorn region, where the Calitzdorp hot spring is located, was conducted using published geophysical data in the form of a magneto-telluric (MT) survey that was carried out in 2005 by the Agulhas-Karoo Geoscience Transect project. The MT data was presented in a paper by Weckmann et al. (2012) as a cross sectional profile from Mossel Bay to Prince Albert to a depth of 30km, where a large region of low resistivity was found below the Oudtshoorn basin. The Calitzdorp hot spring is positioned at the surface above this region. The geological cross sections and regional interpretation presented in this study infers that a major syncline of the Cape Supergroup exists below the basin, potentially as deep as 10km, and covers the low resistivity area from the MT profile. This led to the inference that the large region of low resistivity is most probably due to a large water reservoir. This potential reservoir is about 40km in length with a depth of 2.5km to 7km at its thickest, tapering out towards the edges. The depth to the top of the potential reservoir and the estimated reservoir temperature from the geothermometry results in a geothermal gradient of 39oC/km ±4.3oC/km. Thus Calitzdorp was identified as a promising location for further exploration, ideally deep boreholes or more geophysical surveys, to validate the existence of a reservoir and take down-hole temperature measurements. The depth and size of this potential reservoir would make it a favourable candidate for a pilot low-enthalpy geothermal power plant within the Cape Fold Belt and South Africa.