Abstract
Host rock alterations related to high heat flow associated with igneous intrusions play an important role in changing the reservoir characteristics of oil and gas bearing shales. Such effects are common in the Permian black shale formations of the Karoo Basin that were intruded by basin-wide dolerites in the Early Jurassic (~182 Ma). Distinct changes in mineralogy and cracking of organic matter associated with high heat and fluid flow affect the porosity and permeability of host rocks. Analysis of drill core samples of the Karoo black shales close to upper and lower contacts of the dolerite sills indicates increased quartz content, decrease in hydrous minerals, and formation of metamorphic chiastolite. Most importantly, a notable decrease in the porosity is also observed in these samples.
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Acknowledgments
The authors would like to thank AEON and the Iphakade programme (DST/NRF) for financial support. We also thank Emese Bordy (University of Cape Town) for carefully reviewing this chapter. This is AEON contribution number 158.
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Nengovhela, V., de Wit, M.J., Butcher, A.R., Honse, E. (2016). High-Resolution Petrographical and Chemical Scanning of Karoo Sedimentary Rocks Near Dolerite Sill Contacts Reveals Metamorphic Effects on Shale Porosity. In: Linol, B., de Wit, M. (eds) Origin and Evolution of the Cape Mountains and Karoo Basin. Regional Geology Reviews. Springer, Cham. https://doi.org/10.1007/978-3-319-40859-0_7
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