The investigation of CO2 storage potential in the Zululand Basin in South Africa

As an emerging country, South Africa is heavily reliant on fossil fuels, resulting in significant CO2 emissions. As with all countries, South Africa will require a portfolio of technologies to reduce its CO2 emissions, with carbon capture and storage (CCS) likely to be a particularly important part of this portfolio. There is however, significant uncertainty around the technical potential of CCS in South Africa, as very little data are available for this technology, particularly with respect to CO2 storage. South Africa has no oil production and very little terrestrial gas production, and as a result there has been no substantial oil/gas exploration onshore since the 1970's. To better understand the technical potential of CCS in South Africa, as well as addressing the uncertainty around CO2 storage, the South African government, with the assistance from international governments and local and international industry, established the South African Centre of Carbon Capture and Storage (SACCCS). An Atlas on Geological Storage of Carbon Dioxide in South Africa (Atlas) was published in 2010, concluding that South Africa has 150 Gt of theoretical CO2 storage capacity, 98% of which is offshore. The onshore storage capacity is split between the Algoa and Zululand sedimentary basins, with some additional storage potential in conjunction with enhanced coal bed methane. The Zululand basin forms a potential onshore target for CCS in South Africa, located on the east coast of South Africa in the northern KwaZulu-Natal Province. The basin represents an onshore extension of the southern Mozambique Basin, with basin-fill sediments of late Barremian to late Maastrichtian age. Basin-fill lithologies are subdivided into three formations, the Makatini, Mzinene and St Lucia Formations. Two sandstone packages of specific interest for CO2 storage have been identified with the lowermost Aptian-aged sandstone forming part of the Makatini Formation, and the upper Cenomanian to Turonian-aged sandstone occurring along the contact between the Mzinene and St Lucia Formations. The Aptian-age sandstone succession is identified at depths between 1200-1800 m extending over an area of similar to 1680 km(2). It occurs as a 100-250 m thick, interbedded succession of sandstone and siltstone, with subordinate claystone. Sandstone porosities range from 8-18% but permeabilities are extremely low. The stratigraphically higher Cenomanian to Turonian-age sandstone succession is developed as a 20 to 200 m thick package of interbedded sandstone and siltstone, with similar to 30 m of laterally extensive, clean, gritty, quartz sandstone. The succession occurs at depths ranging from 900 m to <50 m with a consistent south-westward up-dip profile. Porosities range of 15-25% with an average permeability of 229 mD. In 2013, SACCCS assembled the PCSP Advisory Committee (PAC) to provide external technical input and review to the development of the PCSP. For the first meeting of the PAC, they were asked, based on the basin-scale assessments of the Zululand and Algoa basins, to advise on the likelihood that SACCCS will be able to identify a site for the storage of 10-50,000t CO2. The PAC in their review report, complemented the depth of work done on the Zululand however recommended that more information could yet be extracted from the existing data prior to deciding whether or not to progress to the acquisition of new geological data, especially given the costs associated with such data acquisition. SACCCS is now working to address these recommendations and will make use of support committed from the World Bank for their completion. (C) 2014 The Authors. Published by Elsevier Ltd.