An evaluation of the coal bed methane potential of the Mid-Zambezi and North Eastern Kalahari Karoo basins
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Date
2017
Authors
Potgieter, Johannes Hermanus Jacobus
Journal Title
Journal ISSN
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Publisher
University of the Free State
Abstract
With the growing energy demand worldwide it is very important to identify any new
fossil fuel resources for future use. Coal remains the most widely used fossil fuel for
electricity generation in Southern Africa but over the past two decades gas has been
seen as a possible supplement and ultimate replacement for the coal. A lack of
world class conventional gas accumulations in Southern Africa, unconventional gas
deposits, hosted in the Karoo Supergroup, have been investigated as an alternative
gas source. The primary unconventional resource focused on in north-eastern
Botswana and north-western Zimbabwe to date has been coal bed methane (CBM),
a natural gas generated during the coalification process and stored within internal
coal structures. A major limiting factor for a regional investigation into the CBM
resource potential is the lack of exploration information specifically focused on gas
rather than coal. The gas saturation state of coal has a notable impact on the
measureable 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 is
fully saturated, which has not been the case from dedicated gas exploration
campaigns in the region. As part of this evaluation the coal ranks, obtained from
historic borehole data over the study area, were compared to the laboratory
measured maximum sorptive capacities to determine the theoretical gas content of
the coal. Investigations of two regional analogous coal fields showed that the coals
are unlikely to be fully saturated and for a resource evaluation based on coal rank it
is imperative to use a range of saturations for the final data inputs. Schlumberger’s
GeoX software was used for a probabilistic resource calculation using Monte Carlo
simulations with ten thousand iterations. The resource estimation results showed a
wide distribution of probable values. Even with a resource value of 22Tcf, the major
basins in Canada and the US have significantly higher resource densities than that
of the Study Area indicating a lower prospectivity for CBM.
Description
Keywords
Coal bed methane, Coal, Saturation Kalahari Karoo Basin, Mid-Zambezi Basin, Karoo Supergroup, Wankie, Nata, Power resources, Dissertation (M.Sc. (Geology))--University of the Free State, 2017