Deflating the shale gas potential of South Africa’s Main Karoo basin
The Main Karoo basin has been identified as a potential source of shale gas (i.e. natural gas that can be extracted via the process of hydraulic stimulation or ‘fracking’). Current resource estimates of 0.4–11x109 m3 (13–390 Tcf) are speculatively based on carbonaceous shale thickness, area, depth,...
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| Format: | Article |
| Language: | English |
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Academy of Science of South Africa
2017-09-01
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| Series: | South African Journal of Science |
| Subjects: | |
| Online Access: | https://www.sajs.co.za/article/view/4125 |
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| author | Michiel O. de Kock Nicolas J. Beukes Elijah O. Adeniyi Doug Cole Annette E. Götz Claire Geel Frantz-Gerard Ossa |
| author_facet | Michiel O. de Kock Nicolas J. Beukes Elijah O. Adeniyi Doug Cole Annette E. Götz Claire Geel Frantz-Gerard Ossa |
| author_sort | Michiel O. de Kock |
| collection | DOAJ |
| description | The Main Karoo basin has been identified as a potential source of shale gas (i.e. natural gas that can be extracted via the process of hydraulic stimulation or ‘fracking’). Current resource estimates of 0.4–11x109 m3 (13–390 Tcf) are speculatively based on carbonaceous shale thickness, area, depth, thermal maturity and, most of all, the total organic carbon content of specifically the Ecca Group’s Whitehill Formation with a thickness of more than 30 m. These estimates were made without any measurements on the actual available gas content of the shale. Such measurements were recently conducted on samples from two boreholes and are reported here. These measurements indicate that there is little to no desorbed and residual gas, despite high total organic carbon values. In addition, vitrinite reflectance and illite crystallinity of unweathered shale material reveal the Ecca Group to be metamorphosed and overmature. Organic carbon in the shale is largely unbound to hydrogen, and little hydrocarbon generation potential remains. These findings led to the conclusion that the lowest of the existing resource estimates, namely 0.4x109 m3 (13 Tcf), may be the most realistic. However, such low estimates still represent a large resource with developmental potential for the South African petroleum industry. To be economically viable, the resource would be required to be confined to a small, well-delineated ‘sweet spot’ area in the vast southern area of the basin. It is acknowledged that the drill cores we investigated fall outside of currently identified sweet spots and these areas should be targets for further scientific drilling projects.
Significance:
• This is the first report of direct measurements of the actual gas contents of southern Karoo basin shales.
• The findings reveal carbon content of shales to be dominated by overmature organic matter.
• The results demonstrate a much reduced potential shale gas resource presented by the Whitehill Formation. |
| first_indexed | 2024-12-10T11:17:53Z |
| format | Article |
| id | doaj.art-38bce20dcd1a4d8c812004c7688045da |
| institution | Directory Open Access Journal |
| issn | 1996-7489 |
| language | English |
| last_indexed | 2024-12-10T11:17:53Z |
| publishDate | 2017-09-01 |
| publisher | Academy of Science of South Africa |
| record_format | Article |
| series | South African Journal of Science |
| spelling | doaj.art-38bce20dcd1a4d8c812004c7688045da2022-12-22T01:51:05ZengAcademy of Science of South AfricaSouth African Journal of Science1996-74892017-09-011139/10121210.17159/sajs.2017/201603314125Deflating the shale gas potential of South Africa’s Main Karoo basinMichiel O. de Kock0Nicolas J. Beukes1Elijah O. Adeniyi2Doug Cole3Annette E. Götz4Claire Geel5Frantz-Gerard Ossa6DST-NRF CIMERA, Department of Geology, University of Johannesburg, Johannesburg, South AfricaDST-NRF CIMERA, Department of Geology, University of Johannesburg, Johannesburg, South AfricaDST-NRF CIMERA, Department of Geology, University of Johannesburg, Johannesburg, South AfricaCouncil for Geoscience, Pretoria, South AfricaSchool of Earth and Environmental Sciences, University of Portsmouth, Portsmouth, United KingdomDepartment of Geological Sciences, University of Cape Town, Cape Town, South AfricaDST-NRF CIMERA, Department of Geology, University of Johannesburg, Johannesburg, South AfricaThe Main Karoo basin has been identified as a potential source of shale gas (i.e. natural gas that can be extracted via the process of hydraulic stimulation or ‘fracking’). Current resource estimates of 0.4–11x109 m3 (13–390 Tcf) are speculatively based on carbonaceous shale thickness, area, depth, thermal maturity and, most of all, the total organic carbon content of specifically the Ecca Group’s Whitehill Formation with a thickness of more than 30 m. These estimates were made without any measurements on the actual available gas content of the shale. Such measurements were recently conducted on samples from two boreholes and are reported here. These measurements indicate that there is little to no desorbed and residual gas, despite high total organic carbon values. In addition, vitrinite reflectance and illite crystallinity of unweathered shale material reveal the Ecca Group to be metamorphosed and overmature. Organic carbon in the shale is largely unbound to hydrogen, and little hydrocarbon generation potential remains. These findings led to the conclusion that the lowest of the existing resource estimates, namely 0.4x109 m3 (13 Tcf), may be the most realistic. However, such low estimates still represent a large resource with developmental potential for the South African petroleum industry. To be economically viable, the resource would be required to be confined to a small, well-delineated ‘sweet spot’ area in the vast southern area of the basin. It is acknowledged that the drill cores we investigated fall outside of currently identified sweet spots and these areas should be targets for further scientific drilling projects. Significance: • This is the first report of direct measurements of the actual gas contents of southern Karoo basin shales. • The findings reveal carbon content of shales to be dominated by overmature organic matter. • The results demonstrate a much reduced potential shale gas resource presented by the Whitehill Formation.https://www.sajs.co.za/article/view/4125Ecca GroupWhitehill Formationhydrocarbonthermal maturityenergy resource |
| spellingShingle | Michiel O. de Kock Nicolas J. Beukes Elijah O. Adeniyi Doug Cole Annette E. Götz Claire Geel Frantz-Gerard Ossa Deflating the shale gas potential of South Africa’s Main Karoo basin South African Journal of Science Ecca Group Whitehill Formation hydrocarbon thermal maturity energy resource |
| title | Deflating the shale gas potential of South Africa’s Main Karoo basin |
| title_full | Deflating the shale gas potential of South Africa’s Main Karoo basin |
| title_fullStr | Deflating the shale gas potential of South Africa’s Main Karoo basin |
| title_full_unstemmed | Deflating the shale gas potential of South Africa’s Main Karoo basin |
| title_short | Deflating the shale gas potential of South Africa’s Main Karoo basin |
| title_sort | deflating the shale gas potential of south africa s main karoo basin |
| topic | Ecca Group Whitehill Formation hydrocarbon thermal maturity energy resource |
| url | https://www.sajs.co.za/article/view/4125 |
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