Recent investigations of the shale gas potential in the main Karoo Basin have concentrated on the Whitehill Formation within the Ecca Group. This study focuses on the shale gas potential of the underlying Prince Albert Formation using the parameters of volume porosity, permeability, total organic carbon (TOC), vitrinite reflectance and Rock-Eval data. Shale samples were retrieved from three surface localities in the southern part of the main Karoo Basin and from core of three boreholes drilled through the Prince Albert Formation near Ceres, Mervewille and Willowvale. The sampling localities occur near the borders of the prospective shale gas areas (“sweet spots”) identified for the Whitehill Formation. Kerogen was found to be Type IV with hydrogen indices less than 65 mg/g. Shale porosities are between 0.08 and 5.6% and permeabilities between 0 and 2.79 micro-Darcy, as determined by mercury porosimetry. TOC varies between 0.2 and 4.9 weight % and vitrinite reflectance values range from 3.8 to 4.9%. Although the porosity and TOC values of the Prince Albert Formation shales are comparable with, but at the lower limits of, those of the gas-producing Marcellus shale in the United States (porosities between 1 and 6% and TOC between 1 and 10 weight %), the high vitrinite reflectance values indicate that the shales are overmature with questionable potential for generating dry gas. This overmaturity is probably a result of an excess depth of burial, tectonic effects of the Cape Orogeny and dolerite intrusions. However, viable conditions for shale gas might exist within the “sweet spot” areas, which were defined for the Whitehill Formation.
The Prince Albert Formation is a mudstone-dominated unit, which is located in the central and southwestern part of the Main Karoo Basin and the southernmost part of the Kalahari Basin in South Africa. It is Early Permian (Artinskian to early Kungurian) in age and is stratigraphically located between the underlying Dwyka Group and the overlying Whitehill Formation. In the Main Karoo Basin, its regional extent is limited to the cut-off boundary of the Whitehill Formation along a line from Hertzogville in the Free State to Coffee Bay in the Eastern Cape. Northeast of this boundary, it correlates with the lower part of the undifferentiated Ecca Group known as “Ecca Shales” and in the northern part of the basin, north of a line from Bloemfontein (Free State) to Harding (KwaZulu-Natal), with the Vryheid and Pietermaritzburg formations. The Prince Albert Formation is generally between 50 and 200 m thick, including the type area around Prince Albert, where a thickness of about 145 m was measured. It is thicker (230 to 497 m) in the region between Brandvlei and Jansenville and thins northeastwards to between about 30 and 60 m in the area between Kimberley and East London. In the Kalahari Basin, the formation is only 25 to 50 m thick, due to post-Karoo erosion of its upper part. The Prince Albert Formation contains fossils of marine invertebrates, palaeoniscoid fish, sharks, sponge spicules, foraminiferans, radiolarians, acritarchs, fragments of wood and leaves, together with ichnofossils in the form of fish trails, arthropod trackways and invertebrate burrows. High Rb/K ratios in the mudstones also indicate a marine shelf environment with suspension settling of mud being the predominant depositional process. Sedimentation was initiated during a major transgressive event following final melting of Dwyka Group associated ice sheets in southern Gondwana in the Late Palaeozoic. Water depths in the basin were probably about 400 m, but shallowed northeastward. In the proximal part of the basin northeast of Kimberley, sandstones in coarsening-upward successions represent prograding deltaic deposits derived from an adjacent source area to the north.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.