Early diagenetic signals archived in black shales of the Dwyka and Lower Ecca Groups of the southern Karoo Basin (South Africa): Keys to the deglaciation history of Gondwana during the Early Permian, and its effect on potential shale gas storage

2018 ◽  
Vol 121 (1) ◽  
pp. 69-94 ◽  
Author(s):  
H.-M. Schulz ◽  
B. Linol ◽  
M. de Wit ◽  
B. Schuck ◽  
I. Schaepan ◽  
...  
Keyword(s):  
South Africa ◽  
Shale Gas ◽  
Gas Storage ◽  
Black Shales ◽  
Early Permian ◽  
Karoo Basin ◽  
History Of

Shale gas leakage in lower Ecca shales during contact metamorphism by dolerite sill intrusions in the Karoo Basin, South Africa

2021 ◽  
Author(s):  
V. Nengovhela ◽  
B. Linol ◽  
L. Bezuidenhout ◽  
T. Dhansay ◽  
T Muedi ◽  
...  
Keyword(s):  
South Africa ◽  
Grain Boundaries ◽  
Shale Gas ◽  
Elevated Temperatures ◽  
Contact Metamorphism ◽  
Microscopy Imaging ◽  
Gas Leakage ◽  
Karoo Basin ◽  
Maximum Temperatures ◽  
Host Rocks

Abstract Contact metamorphism along widespread dolerite sills and dykes, emplaced at 182 to 183 Ma through the sedimentary host rocks of the Karoo Basin, triggered devolatilization of carbon-rich shales of the Lower Ecca Group. Hornfel samples collected from drill cores that intersect dolerite sills were analyzed for mineral phase equilibria, chemistry and porosity to characterize thermal aureoles at various distances from sill intrusions. Andalusite-chiastolite and cordierite porphyroblasts with biotite and muscovite occur within 10 to 20 m of many intrusive contacts. These metamorphic minerals crystallized when host shales attained maximum temperatures ranging between 450 and 600°C. Scanning electron microscopy imaging confirms that the hornfels are compact and that their metamorphic minerals limit porosity along grain boundaries. In few cases intra-mineral porosity occurs within individual crystals such as calcite, andalusite and cordierite. Disequilibrium metamorphic textures such as irregular grain boundaries, and inclusions in andalusite and cordierite reveal that the elevated temperatures were too short-lived to accomplish complete (re)crystallization. Thermal modeling results are consistent with the observed metamorphic mineral assemblages. Gas leakage calculations along a 7 m and a 47 m thick dolerite sill that intrude toward the top of the Whitehill Formation suggest that methane volumes ranging between 8 to 15 Tcf were generated during the sill emplacement. Methane was likely released into the atmosphere through hydrothermal vent complexes that are well preserved in the western Karoo Basin. If such loss was widespread across the entire basin, the implications for paleo-climate change and preserved shale gas reserves in the Karoo Basin of South Africa would be significant.

A Weichselian deglaciation model applied to the Early Permian glaciation in the northeast Karoo Basin, South Africa

2001 ◽  
Vol 16 (6) ◽  
pp. 583-593 ◽  
Author(s):  
Sylvi Haldorsen ◽  
Victor Von Brunn ◽  
Rodney Maud ◽  
Edward D. Truter
Keyword(s):  
South Africa ◽  
Early Permian ◽  
Karoo Basin

scholarly journals Prospective policy safeguards to mitigate hydrogeological risk pathways in advance of shale gas development in the Karoo basin, South Africa

2020 ◽  
pp. 100499
Author(s):  
Kevin Pietersen ◽  
Luc Chevallier ◽  
Audrey Levine ◽  
Thandokazi Maceba ◽  
Zaheed Gaffoor ◽  
...  
Keyword(s):  
South Africa ◽  
Shale Gas ◽  
Karoo Basin

Seismic imaging of dolerite sills and volcanic vents in the Central Karoo, South Africa: implications for shale gas potential

2021 ◽  
Author(s):  
S.E. Scheiber-Enslin ◽  
M. Manzi ◽  
S.J. Webb
Keyword(s):  
South Africa ◽  
Shale Gas ◽  
Global Climate ◽  
Magnetic Data ◽  
Seismic Reflection Profile ◽  
Magnetic Studies ◽  
Seismic Line ◽  
Seismic Section ◽  
Karoo Basin ◽  
Gas Potential

Abstract The Karoo Basin of South Africa covers an area of 700 000 km2 and has been identified as a possible shale gas reserve. Any evaluation of the shale gas potential of the basin must consider the widespread dolerite dykes and sills. These intrusions were emplaced into the Karoo Supergroup and are well dated at around 183 Ma. Their intrusion triggered the explosive releases of gas in the basin, marked on surface by breccia pipes and hydrothermal vents. This outpouring of gas has been proposed as a significant contributor to global climate change. Research into the three-dimensional interconnected structure of these dolerite sills and dykes and their interaction with the hydrocarbon rich layers in the lower part of the Karoo Supergroup has been limited to localized observations of outcrop, magnetic data, legacy seismic data (from the 1970s) and well core. Here we present an interpreted 65 km long higher-resolution 2D seismic reflection profile across the Karoo Basin, approximately 100 km southeast of Trompsburg. These data were collected in the 1990s and at the time deeper structures along the line interpreted. In this study we focus on the top 0.6 to 2 seconds TWT of the data. The seismic line images the interconnected and cross cutting nature of the dolerite dykes and sills along the profile. We also report possible evidence of a gas escape structure (approximately 2.5 km in diameter at surface) emerging near the edge of a dolerite sill in close proximity to the Whitehill Formation, which is the main target for shale gas exploration. This suggests that gas vents in the eastern Karoo Basin close to Lesotho are due to the release of gas from the carbonaceous shales of the Ecca Group. This is similar to breccia pipes mapped on surface in the western part of the Karoo Basin. This seismic section highlights why dolerite sills and dykes must be considered when evaluating the shale gas potential of the Karoo Basin. We propose that better characterization of the Karoo Basin subsurface by seismic and magnetic studies is necessary prior to any efforts to calculate shale gas reserves.

scholarly journals Refining the chronostratigraphy of the Karoo Basin, South Africa: magnetostratigraphic constraints support an early Permian age for the Ecca Group

2017 ◽  
Vol 211 (3) ◽  
pp. 1354-1374 ◽  
Author(s):  
Mercedes E. Belica ◽  
Eric Tohver ◽  
Miquel Poyatos-Moré ◽  
Stephen Flint ◽  
Luis A. Parra-Avila ◽  
...  
Keyword(s):  
South Africa ◽  
Early Permian ◽  
Karoo Basin
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