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This work is protected by copyright and other intellectual property rights and duplication or sale of all or part is not permitted, except that material may be duplicated by you for research, private study, criticism/review or educational purposes. Electronic or print copies are for your own personal, non- commercial use and shall not be passed to any other individual. No quotation may be published without proper acknowledgement. For any other use, or to quote extensively from the work, permission must be obtained from the copyright holder/s. Energy potential of the Ecca Group from the southern Main Karoo Basin, South Africa Stuart Alexander Campbell Doctor of Philosophy December 2018 Dedication To my mother and brother for their unwavering support Familia Ante Omnia i Abstract Energy shortages and sporadic, controlled blackouts have been a defining feature of South Africa’s aging national energy grid for more than a decade. To investigate local energy sources from shale gas, two boreholes were drilled in the southern Main Karoo Basin into the Permian- aged Ecca Group by the Karoo Research Initiative. Borehole KZF-1 (Western Cape) intersected thick shale successions of the lower Ecca Group and revealed the stratigraphic duplication of the Whitehill (shale gas target) and Prince Albert Formations. This structural deformation was most likely as a result of the organic-rich formations, acting as a decollement for thrust faults related to the north-south directed compression of the Cape Orogeny. Reservoir compartmentalisation and gas escape along porous fault zones hinder hydrocarbon exploration in the area. Borehole KWV-1 (Eastern Cape) revealed thick successions of turbiditic sandstones and a moderately elevated geothermal gradient. The clastic rocks have low permeabilities and high thermal conductivities. Analysis of the petro- and thermophysical data from the Ripon Formation sandstones, from both the core and nearby Ecca Pass outcrop location, show the potential of the formation as an Enhanced Geothermal Reservoir, with temperatures exceeding 100°C being suitable for energy production from a binary geothermal power plant. The comparison of combined gamma-ray logs, geothermal potential of samples (specific heat capacity, thermal diffusivity, and thermal conductivity) and lithological logs show a correlation between lithological composition and geothermal reservoir potential that can be identified in gamma-ray log patterns. These correlations can be extrapolated for purposes of geothermal exploration in non-cored nearby boreholes. The numerous pre-existing faults, decreasing from the basin’s southern margin towards the basin interior, elevate the risk of inducing seismic events from the use of reservoir stimulation techniques associated with energy exploration, as well as wastewater management associated with future extraction activities. ii Table of Contents 1. Introduction ......................................................................................................................... 1 1.1. Aims and Objectives .................................................................................................... 4 1.2. Methodology Overview ............................................................................................... 5 1.3. Summary of remaining chapters .................................................................................. 6 2. Geological Setting ............................................................................................................... 7 2.1. Overview ...................................................................................................................... 7 2.2. Regional Tectonic Framework ..................................................................................... 8 2.3. Cape Fold Belt............................................................................................................ 11 2.3.1. Age Constraints ................................................................................................... 13 2.4. Stratigraphy of the Karoo Supergroup ....................................................................... 15 2.4.1. Lithostratigraphy ................................................................................................. 17 2.4.2. Biostratigraphy .................................................................................................... 20 2.4.3. Age Constraints ................................................................................................... 20 2.5. The Ecca Group .......................................................................................................... 23 2.5.1. Overview ............................................................................................................. 23 2.5.2. Prince Albert Formation ..................................................................................... 26 2.5.3. Whitehill Formation ............................................................................................ 27 2.5.4. Collingham Formation ........................................................................................ 31 2.5.5. Ripon Formation ................................................................................................. 33 2.5.6. Tierberg Formation ............................................................................................. 36 2.5.7. Marine versus non-marine .................................................................................. 37 iii 2.5.8. Dolerite Intrusions .............................................................................................. 39 2.5.9. Energy Potential .................................................................................................. 41 2.6. Conclusions ................................................................................................................ 46 3. Permian black shales of the Karoo Basin: Structural controls and implications for shale gas resource potential ............................................................................................................... 48 3.1. Introduction ................................................................................................................ 48 3.2. Black Shales ............................................................................................................... 49 3.2.1. Composition ........................................................................................................ 50 3.2.2. Depositional Environments ................................................................................ 50 3.2.3. Hydrocarbon Potential ........................................................................................ 52 3.2.4. Age Constraints .................................................................................................. 52 3.3. Preservation and Depositional Mechanisms .............................................................. 54 3.4. Structural Controls on Hydrocarbon Permeability ..................................................... 56 3.4.1. Reservoir Compartmentalisation ........................................................................ 56 3.4.2. Stratigraphic Compartmentalisation ................................................................... 57 3.4.3. Structural Compartmentalisation ........................................................................ 57 3.5. Borehole KZF-1 ......................................................................................................... 59 3.5.1. Location .............................................................................................................. 59 3.5.2. Lithological and petrophysical data .................................................................... 60 3.5.3. Stratigraphic Duplication .................................................................................... 69 3.5.4. Downhole Geophysical Data .............................................................................. 74 3.6. Discussion .................................................................................................................. 80 iv 3.6.1. Syn-sedimentary vs. tectonic deformation .......................................................... 80 3.6.2. Effects on Shale Gas Potential ............................................................................ 86 3.6.3. Structural Controls .............................................................................................. 89 3.7. Conclusions ................................................................................................................ 90 4. Geothermal Energy from the Main Karoo Basin: A Study of Permian Sandstone Reservoir Formations ................................................................................................................................ 92 4.1. Introduction ................................................................................................................ 92 4.2. The Hydrological Properties of the Main Karoo Basin ............................................. 94 4.3. Geothermal Energy .................................................................................................... 96 4.3.1. Porosity and Permeability ................................................................................... 97 4.3.2. Thermophysical Rock Properties ........................................................................ 98 4.3.3. Thermofacies Concept .......................................................................................
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