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

摘要

The potential shale gas resource of the Karoo Supergroup (Figure 1), and specifically the ~30-m thick WhitehillFormation of the Ecca Group, remains highly speculative. 1-7 An original ~18x10 9 m 3 or 485 trillion cubic feetresource estimate 8 – which would make the Karoo basin the fourth largest resource in the world – is certainly grosslyinflated. Trillion cubic feet or Tcf is the unit in which widely published resource estimates are quoted and are providedthroughout this contribution in brackets wherever resource estimates are listed in SI units. The United States EnergyInformation Administration downgraded this estimate to place the Karoo basin as the sixth largest global resourceat 11x10 9 m 3 (390 Tcf), of which the Whitehill Formation contributed ~6x10 9 m 3 (211 Tcf). 3 Conservative estimatesare much smaller. Preliminary scenarios of 0.9–8x10 9 m 3 (32–287 Tcf) were calculated as alternatives to the USestimate. 1 Subsequent work has resulted in best estimates closer to the smaller conservative value cited above.Deterministic gas estimates of 1–1.2x10 9 m 3 (36–42 Tcf) were calculated for the Whitehill Formation. 4 Comparable tothis amount is the probabilistic estimate of 1.4x10 9 m 3 (49 Tcf), but with a large uncertainty interval of 0.4–4.9x10 9 m 3(14–172 Tcf). 5 A speculated technically recoverable shale gas resource of 0.37x10 9 m 3 (13 Tcf) for the WhitehillFormation and 0.54–0.65x10 9 m 3 (19–23 Tcf) recoverable free gas represent the lower end of estimates.