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

AbstractAs 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 ∼1680 km2. 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 ∼30 m of laterally extensive, clean, gritty, quartz sandstone. The succession occurs at depths ranging from 900 m to