--> --> Reservoir Characterization from Lithofacies and Petrophysical Analyses of the Clastic Sediments in the Southern Pletmos Basin, South Africa

2018 AAPG International Conference and Exhibition

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Reservoir Characterization from Lithofacies and Petrophysical Analyses of the Clastic Sediments in the Southern Pletmos Basin, South Africa

Abstract

The Southern Pletmos Basin, located along the south coast of South Africa, is a proven hydrocarbon reservoir but still under-explored due to a distinct paucity in the knowledge of its architectural and internal reservoir properties that can aid optimal production. Hence the prime aim of the study is to examine the lithofacies distribution and rock properties within the reservoir using both sedimentological and petrophysical methods, so as to characterize the reservoir quality and the extent of sedimentation. This study involved an integration of wireline logs and drill core analysis from wellbores with the aid of petroleum software (Interactive Petrophysics and Petrel©) platforms. Core descriptions were done from the drilling cores and selected samples taking for laboratory investigation which include scanning electron microscopic and thin sections analysis for sedimentological characterization. Petrographically porosity and permeability from the porous space in the rock were determined. Log normalization was done and the lithologic logs were used to distinguish the sand/shale cutoff, connective porosity, deep-resistivity responses, acoustic transit time, bulk and grains density and neutron porosity. The logs’ curves were calibrated with cores to identify thresholds based on various zonations. Lithologically the reservoir comprises dominantly of sandstone with interbedded shale and mudstone. The sandstone mineralogy consists mainly of quartz, and subordinate feldspars and lithic (rock-fragments). The major sedimentary features are planar and cross-bedding, pebbly mudstones, and sand-in-shale pinch-outs. The distortion and detachment of the silty/mud or sandy strata results in a high heterogeneity of the lateral continuity of the sandy constituents. A regional well-log lithofacies was established from which the reservoir sand and physical rock properties (porosity, fluid saturation and permeability) were determined. There is spatial variation in distribution and quality of the reservoir based on the lithofacies. The fluid properties give an indication of good storage capacity. The study demonstrates that combination of sediments’ framework in relation to the primary rock properties, and the sedimentary process are reliable method to determine the prospectivity of hydrocarbon potential. The results from this study can further be used for simulation and compilation of a 3D sedimentological model. Keyword: Lithofacies, sandstone, reservoir and hydrocarbon.