Unconventional and Renewable Energy Resources

Shale Gas Potential of the Karoo Basin

In response to the so-called Shale Gas Revolution in the USA, that has turned the country from a net importer to exporter of fossil fuels in under 10 years, worldwide interest has been shown in other deeply-buried sedimentary rocks that have the right age, that were deposited in the right environments to possibly have contained significant organic material and that underwent the necessary burial history. A study on world shale reserves conducted by the Energy Information Agency (EIA) in 2013 concluded that there could be as much as 390 Tcf (trillion cubic feet) recoverable reserves of shale gas in the southern and southwestern parts of the South African Karoo Basin. This would make it the 5th-largest shale gas resource in the world.

However, South Africa’s geoscientists know very little about the possibility of shale gas deposits in the Karoo Basin and much of the existing data is of insufficient quality to address the current questions. Some of the particular unique geological features of the basin are:

  1. The southern parts of the basin, which would be the most prospective according to the EIA Report, lie in close proximity to the Cape Fold Belt, a major mountain chain that formed between 280 and 230 Million years ago and that would have significantly disturbed the deep structure and thermal history of the rocks, with possible significant implications for any volatile hydrocarbon deposits that may have been ‘cooked off’ and escaped through microstructural cleavage and larger faults. The rock strata in this area are also not horizontal, which may have assisted further in escape of any volatiles. Also, this southern area coincides with the deepest part of the basin and some shales could be overmature for gas generation owing to excessively deep burial.
  2. Much of the basin has been invaded by dolerite sills and dykes associated with the 183 million year old breakup of Gondwana. The Karoo Igneous Province represents one of the largest magmatic events in Earth’s history and could have substantially raised the geothermal gradient within the Karoo sedimentary rocks at the time when they were most deeply buried, with further consequences for volatile hydrocarbons. The sills and dykes have also created a compartmentalised structure in the basin, a feature that is well known from shallow groundwater reservoir studies, with the impermeable dolerites often preventing vertical and horizontal migration of water over significant distances.
  3. Although not unique, a further point of note is the role of the topographic relief generated by the Cape Fold Mountains along the southern margin of the basin, which influences deep-level artesian water circulation through the rocks.

From this background, geoscientists from six of South Africa’s leading universities (University of Pretoria, University of the Witwatersrand, University of Johannesburg, University of the Free State, University of Cape Town, Stellenbosch University) and the Council for Geoscience have undertaken to focus their joint research efforts in a coordinated, multi-disciplinary project called the Karoo Research Initiative (KARIN) led by Prof. Annette E. Götz, University of Pretoria. KARIN is incorporated under the newly-established NRF-DST Centre of Excellence for Integrated Mineral and Energy Resource Analysis (CIMERA) that is co-hosted by the University of Johannesburg and University of the Witwatersrand.

Geothermal Energy from Deep Sedimentary Basins

Worldwide growth in renewable energy sources makes research in the field of geothermal energy a challenging task for geoscientists. Whilst high enthalpy, volcanic settings have been the focus in the past, geothermal reservoir characterization of low and mid enthalpy systems linked to deep sedimentary basins, as well as the development of analytical and numerical tools for identification, operation, stimulation and sustainable utilization of such geothermal reservoirs are key points to address in the future.

Geothermal power projects drill wells to extract heat by producing hot water or steam from a permeable reservoir through the wells and pipelines into turbines on the surface, where thermal energy is converted to electricity. The cooled water and condensed steam are then injected back into the reservoir for reheating. Worldwide deep sedimentary basins may contain 70 to 80% of technically extractable geothermal resources and sustainability of fluid flow and temperature must be assessed so as to explain the economic potential of a specific resource.

Furthermore, the assessment of the potential of deep sedimentary basins with respect to geothermal power generation in conjunction with carbon capture and storage (CCS) may substantially contribute to global-warming mitigation.

Recent research at UP focuses on geothermal resources of sedimentary basins in Central Europe, China and Mexico.


- Author AE Götz

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