An evaluation of the coal bed methane potential of the Mid-Zambezi and North Eastern Kalahari Karoo basins

[摘要] With the growing energy demand worldwide it is very important to identify any newfossil fuel resources for future use. Coal remains the most widely used fossil fuel forelectricity generation in Southern Africa but over the past two decades gas has beenseen as a possible supplement and ultimate replacement for the coal. A lack ofworld class conventional gas accumulations in Southern Africa, unconventional gasdeposits, hosted in the Karoo Supergroup, have been investigated as an alternativegas source. The primary unconventional resource focused on in north-easternBotswana and north-western Zimbabwe to date has been coal bed methane (CBM),a natural gas generated during the coalification process and stored within internalcoal structures. A major limiting factor for a regional investigation into the CBMresource potential is the lack of exploration information specifically focused on gasrather than coal. The gas saturation state of coal has a notable impact on themeasureable gas content value as well as the production potential within an area.One of the assumptions of previous semi-regional assessments was that the coal isfully saturated, which has not been the case from dedicated gas explorationcampaigns in the region. As part of this evaluation the coal ranks, obtained fromhistoric borehole data over the study area, were compared to the laboratorymeasured maximum sorptive capacities to determine the theoretical gas content ofthe coal. Investigations of two regional analogous coal fields showed that the coalsare unlikely to be fully saturated and for a resource evaluation based on coal rank itis imperative to use a range of saturations for the final data inputs. Schlumberger'sGeoX software was used for a probabilistic resource calculation using Monte Carlosimulations with ten thousand iterations. The resource estimation results showed awide distribution of probable values. Even with a resource value of 22Tcf, the majorbasins in Canada and the US have significantly higher resource densities than thatof the Study Area indicating a lower prospectivity for CBM.

[发布机构] University of the Free State