Deflating the shale gas potential of South Africa’s Main Karoo basin

Abstract

The Main Karoo basin has been identified as a potential source of shale gas (i.e. natural gas that can be extracted via the process of hydraulic stimulation or ‘fracking’). Current resource estimates of 0.4–11x109 m3 (13–390 Tcf) are speculatively based on carbonaceous shale thickness, area, depth, thermal maturity and, most of all, the total organic carbon content of specifically the Ecca Group’s Whitehill Formation with a thickness of more than 30 m. These estimates were made without any measurements on the actual available gas content of the shale. Such measurements were recently conducted on samples from two boreholes and are reported here. These measurements indicate that there is little to no desorbed and residual gas, despite high total organic carbon values. In addition, vitrinite reflectance and illite crystallinity of unweathered shale material reveal the Ecca Group to be metamorphosed and overmature. Organic carbon in the shale is largely unbound to hydrogen, and little hydrocarbon generation potential remains. These findings led to the conclusion that the lowest of the existing resource estimates, namely 0.4x109 m3 (13 Tcf), may be the most realistic. However, such low estimates still represent a large resource with developmental potential for the South African petroleum industry. To be economically viable, the resource would be required to be confined to a small, well-delineated ‘sweet spot’ area in the vast southern area of the basin. It is acknowledged that the drill cores we investigated fall outside of currently identified sweet spots and these areas should be targets for further scientific drilling projects.

Marine flooding surfaces recorded in Permian black shales and coal deposits of the Main Karoo Basin (South Africa): Implications for basin dynamics and cross-basin correlation

“…Palynological data from the Ecca Pass suggest a Roadian age (Götz, 2015) consistent with the radiometric dates of McKay et al (2015). Present-day total organic carbon (TOC) values range from less than 1.0% up to 2.8% (Geel et al, 2015;De Kock et al, 2017;this study, Tab. 2).…”

“…Olive grey to dark-grey silty shale with intercalated fine-grained sandstone layers occur in the northern part of the basin, whereas darkgrey, pyrite-bearing shale with chert and phosphatic nodules and lenses occurs in the south (Cole, 2005). Present-day total organic carbon (TOC) values range from less than 1.0% up to 3.4% (Aarnes et al, 2011;Geel et al, 2015;De Kock et al, 2017; this study, Tab. 2).…”

South Africa After Paris—Fracking Its Way to the NDCs?

“…Other studies observe that non-CO 2 emissions associated with the production of shale gas, most importantly fugitive methane, 1 The nominal price of electricity increased by over 330 % between the financial years 2008/09 and 2015/16 (ESKOM, 2018). 2 The estimates of the technically recoverable shale gas reserves themselves vary drastically between sources: while the EIA (2015) estimates up to 392 EJ of shale gas to be possibly recoverable, de Kock et al (2017) find in their assessment proof for no more than 13 EJ to be exploitable with current technical measures. might increase life-cycle GHG emissions of this fuel to levels above those of coal combustion, offsetting any benefits for the climate (Howarth et al, 2011;Miller et al, 2013;McJeon et al, 2014;Howarth, 2015).…”

Effect of Hydrofracking on Aquifers

“…Petroleum production has played little to no role in the county's economy to date. It has been estimated that the Karoo Basin hold as much as 13 trillion cubic feet of shale gas [21].…”