--> --> Shale Gas Assessement of the Southern Main Karoo Basin in South Africa

2018 AAPG International Conference and Exhibition

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Shale Gas Assessement of the Southern Main Karoo Basin in South Africa

Abstract

The Petroleum Agency of South Africa assessed the potential technical recoverable shale gas resources with in the Karoo Basin, a ~700 000 km2 geologically complex region commonly described as a retro-arc foreland basin containing marine to continental sediment and that was capped and intruded by the continental flood basalts of the Drakensberg Group. In South Africa the shale gas development is still in its infancy. There is currently no active exploration or production activity, and despite this, the assessment of the potential shale gas resource is required to drive and facilitate policy formulation, decision making and guide future research and exploration. The Petroleum Agency identified the organic rich shale of the Lower Ecca Group as prospective for shale gas and the shale gas play was limited to the Collingham-, Whitehill- and Prince Albert Formations. The shale gas play, for each target formation, was defined and mapped using the 2D seismic data, geochemical data, petrophysical data, public and proprietary literature and recent scientific publications on the Karoo geology. Further to the aforementioned, 1D basin modelling analysis was performed on various swell with the southern region of the Karoo Basin. The 1D basin models were simulated using three basal heat flow models (i.e., Steady State, Transient and Rifting Heat Flow) and varying rates of denudation. The aim of this basin analysis was to evaluate the onset of hydrocarbon generations and the retention capacity of the target formations, for shale gas. The 1D basin modelling analysis indicated that all modelled basal heat flow scenarios yielded generation and retention of gaseous hydrocarbons, but higher yield was achieved with the rifting heat flow model. Both a deterministic and probabilistic volumetric resource assessment was performed for all target formations in the Karoo Basin. The cumulative mean deterministic technically recoverable resources in place is an estimated at 205 trillion cubic feet and the cumulative mean probabilistic technically recoverable resources in place is an estimated 195 trillion. The major sources of geologic risk in the Karoo Basin is associated with free and absorbed gas retention capacities, the thicknesses and extend and the impact of the dolerite intrusions on the hydrocarbon generative and storage capacities of the target formations.