The capture and storage of carbon dioxide (CCS) has been identified as one of the fundamental approaches to mitigating global climate change. The Council for Geoscience has been at the forefront of CCS innovation since 2010, and has produced an atlas on the geological storage of CO2 in South Africa.
This atlas identified possible onshore and offshore repositories within South Africa conforming to the prerequisites for CCS. Since the publication of this atlas, work has focused on three potential storage basins within South Africa, namely the onshore Zululand and Algoa Basins and the offshore Durban Basin. A new project is set to begin, focusing on the potential for site monitoring at the Bongwana natural CO2 gas release near Harding in KwaZulu-Natal.
Bongwana Research Scoping Workshop
In September, the South African Centre for Carbon Capture and Storage (SACCCS) hosted a Research Scoping Workshop for the Bongwana natural CO2 release in KwaZulu-Natal, with the presentations and a field excursion led by Nigel Hicks and Greg Botha of the Council for Geoscience. The three day workshop was attended by fourteen local and international experts, including three experts from the USA and two from the UK.
The first day included a series of presentations about the workshop objective, an overview of SACCCS work and geological presentations by CGS representatives. The second day was a field/site visit which included stops at areas where CO2 is naturally issuing from fault fractures in the region, as well as stops to view basement lithologies which may represent analogues to the CO2 sources. Talks on natural release studies and CO2 monitoring techniques were presented upon returning from the field. The last day of the workshop focused on discussions in order to define the scope for future work at Bongwana and a process for meeting research objectives.
A field excursion was arranged to visit the Bongwana and Umtamvuna River natural CO2 releases occurring along the Bongwan gas fault south of Harding in KwaZulu-Natal. The Bongwan site is located at a bridge over the Umzimkulwana River, where CO2 gas issues from a ~20 m wide fault gouge along the banks of the river. The area is underlain by Dwyka Group tillite which is offset vertically by the fault zone and it is presumed that Marble Delta Formation (Natal Metamorphic Province) carbonate lithologies are present at depth, forming the source of the CO2 gas. It is at this site that a gas bottling factory was erected around 1922 to bottle CO2 for commercial use. No infrastructure except for an old drill pipe remains, however. CO2 samples obtained in 1922 returned carbon dioxide percentages of 98.3 % and 97.6 % for two samples, each with an O2 content of 0.2 %, and nitrogen (by difference) of 1.5 % and 2.2 % respectively.
CO2 springs also occur near Mbizana, where travertine cones are developed on the banks of the Umtamvuna River, which separates KwaZulu-Natal from the Eastern Cape Province. The springs issue from fractures along the Bongwana CO2 fault with a combination of CO2 gas and groundwater being emitted. Studies at this site conducted by researchers in 1997 suggest that the CO2 is likely a reaction taking place at depth at temperatures less than 50 °C, with CO2 equilibrating with groundwater on its way to the surface.
12th International Conference on Greenhouse Gas Technologies
In October, subsequent to the Bongwana workshop, Nigel Hicks attended the GHGT12 conference in Austin, Texas, USA, to present a presentation on work completed in three separate CCS projects in South Africa, as well as to attend a follow-up meeting from the Bongwana workshop. The biannual Greenhouse Gas Control Technologies (GHGT) conference is organised by the International Energy Agency Greenhouse Gas (IEAGHG) R&D Programme. The conference was attended by delegates representing 36 countries, all with an interest in the development of CCS, making the conference a prime opportunity to meet friends and make new contacts. Eleven technical sessions and six panel discussion sessions were held, ranging from geological storage, CO2 capture, transportation, monitoring tools, risk assessments, environmental impacts, legal and regulatory issues to public participation, to name a few.
Nigel Hicks presented three posters on the investigation of storage potential in three of South Africa’s Cretaceous basins, the onshore Zululand Basin in northern KwaZulu-Natal, the onshore Algoa Basin near Port Elizabeth in the Eastern Cape and the offshore Durban Basin in KwaZulu-Natal.
With the use of existing data and information, the geological development and CO2 storage suitability of the basins were assessed through a collaboration of scientists from the Council for Geoscience, Petroleum Agency SA and SACCCS. The basins are structurally complex, hosting a number of horst and graben basement structures which define each of their geometries. Although they have been assigned separate formation nomenclature in specific basins, the basin-fill successions are late Jurassic to Cenozoic in age, with synrift and drift phase sedimentation identified in the basins. A reanalysis of existing legacy 2D seismic and exploration borehole data has been undertaken in the context of CCS to assess the CO2 prospectivity, geological evolution and depositional architecture of the basins identifying potential reservoir-seal pairs that may be suitable for CO2 storage in the deep subsurface.
All three posters were received with great enthusiasm by international delegates in regard to the progression of work coming from South Africa in the CCS industry. With the continuation of work in the Durban Basin as well as potential work on the horizon relating to the Bongwana natural CO2 release, the CCS future in South Africa looks bright.