Application of seismic stratigraphy in reservoir characterisation: a case study of the passive margin deposits of the no
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ORIGINAL PAPER-EXPLORATION GEOLOGY
Application of seismic stratigraphy in reservoir characterisation: a case study of the passive margin deposits of the northern Orange Basin, South Africa Chris Adesola Samakinde1,2 · Jan Marinus Van Bever Donker1 · Ray Durrheim2 · Musa Manzi2 Received: 10 September 2020 / Accepted: 13 November 2020 © The Author(s) 2020
Abstract The Barremian-Cenozoic depositional sequences in the northern Orange Basin, SW, South Africa, were investigated using the principles of seismic stratigraphy to understand the interplay of tectonics and sedimentary processes in the distribution of potential hydrocarbon reservoirs. A seismic stratigraphic workflow (seismic sequence, seismic facies and lithofacies analysis) was completed by utilising three seismic lines (L1, L2 and L3) tied to Wireline data (gamma, checkshots and sonic) in two exploration wells (A1 and A2). Seven depositional sequences were mapped followed by the creation of lithofacies log interpreted from the gamma-ray log (GR) by setting maximum GR value at 60 API for Sandstone, 60–100 API for Siltstone and above 100 API for Shale. Six seismic facies units are recognised based on internal geometry and configurations of the seismic reflectors; Tangential-Oblique (SF1), Hummocky (SF2), Wavy-Parallel (SF3), Chaotic (SF4), Sub-parallel/parallel (SF5) and Divergent (SF6). SF4 is dominant within the Barremian-Aptian sequence and expressed in an incised valley fill, suggesting mass transport deposition accompanied by strong hydrodynamic conditions. Evidence of sedimentary basins progradation is seen within the Late-Albian-Turonian sequences, because of the occurrences of SF2, SF6 and SF 4 facies. SF5 facies is prominent in the Maastrichtian/Campanian sequence, indicating that the deposition of sediments may have been accompanied by uniform margin subsidence after the Late-Cretaceous uplift of the Africa margin. The occurrence of SF1 and SF4 facies within the Cenozoic sequence indicates terrigenous pro-deltaic deposits and mass transport deposits, respectively. Further results from seismic-lithofacies modelling reveal that sand deposits of Barremian-Aptian (SF4 facies unit) and Albian sequences (SF2 and SF6 facies units) are potential stratigraphic reservoirs in this part of the basin. Keywords Facies modelling · Orange Basin · Seismic facies
Introduction As passive margin terrains are structurally less complex than active tectonic regimes, they preserve sedimentary records which can easily be investigated. The application of seismic stratigraphic concepts in the investigation of the sedimentary successions in passive margin settings is critical to the understanding of the palaeo-environments and the geodynamic evolution of sedimentary basins, viz the structural * Chris Adesola Samakinde [email protected] 1
Department of Earth Sciences, University of the Western Cape, Capetown, South Africa
School of Geosciences, University of Witwatersrand, Johannesburg, South Africa
2
styles and depositional systems. Consequently, potential
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