Facies controlled porosity evolution of the Neoproterozoic Upper Bhander Sandstone of Western India
Aabiroo Majid, A. H. M. Ahmad, G. M. Bhat, 2012. "Facies controlled porosity evolution of the Neoproterozoic Upper Bhander Sandstone of Western India", Geology and Hydrocarbon Potential of Neoproterozoic–Cambrian Basins in Asia, G. M. Bhat, J. Craig, J. W. Thurow, B. Thusu, A. Cozzi
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The Upper Bhander Sandstone is dominantly composed of quartzarenites. The basal and top portions are sandstones, with the middle section comprising thinly bedded shales with interlayer silt and sandstone units. The sandstone units are composed of several varieties of quartz, feldspar, micas, rock fragments and heavy minerals. The Upper Bhander Sandstone was deposited in a transgressive phase and later modified by tidal processes and wave- and storm-dominated processes in a tide-influenced Barrier Beach Complex of the shallow marine environment. This study reveals that, during mechanical compaction, a rearrangement of grains took place and point and long contacts were formed. The early silica cementation and shallow burial resulted in high primary porosity. This phase was followed by chemical compaction and the replacement of silica cement by iron cement (Fe-cement) under the deep burial phase of these sandstones. Dissolution of Fe-cement and feldspars resulted in secondary porosity development. Quartz overgrowths are better developed on coarse- to medium-sized grains than on fine-sized grains. These observations suggest a progressive compaction, which initiated at the sediment–water interface and continued till deep burial diagenesis in a rapidly subsiding basin. The existing optical porosity of the Upper Bhander Sandstone is 4% and the minus cement porosity is 18%.
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This volume provides a comprehensive overview of the geology and hydrocarbon potential of the major Neoproterozoic–Cambrian basins of Asia from Oman, across the Middle East and the Indian Subcontinent, to China and SE Siberia, along with new research on the region. Many of these areas (e.g., Oman, Bikaner–Nagaur Basin in India, South China and SE Siberia) host prolific Neoproterozoic–Cambrian petroleum systems with giant to supergiant fields. Three key elements: (1) tectonic stability, (2) relatively late phase of hydrocarbon generation and (3) presence of an effective evaporite seal, seem to be critical for the development of effective Neoproterozoic–Cambrian petroleum systems. These key elements appear of less consequence for the development of ‘unconventional’ hydrocarbons, and the future prospectivity in many of these basins may lie in the exploration for, and production of, shale gas and shale oil directly from the thermally mature, organic-rich source rocks.