Petrography and Diagenetic Evolution of the Proterozoic Kaimur Group Sandstones, Son Valley, India: Implication Towards Reservoir Quality

Abstract

In Central India the Upper Kaimur Subgroup of Vindhyan Supergroup, primarily consists of three lithounits-Dhandraul Sandstone, Scarp Sandstone and Bijaigarh Shale. The framework grains, mineralogy, matrix, pore properties and cements were identified. Average framework composition of the texturally super-mature Dhandraul Sandstone is Qt 99 F 0.1 L 0.8 and texturally less mature, Scarp Sandstone is Qt 99 F 0.2 L 0.8. The important diagenetic components identified based on the framework grain-cement relationships are mechanical compaction, cements, authigenic clays and dissolution and alteration of unstable clastic grains and tec-tonically induced grain fracturing. The early to intermediate stage of the diagnostic realm e.g., mechanical compaction, cementation, dissolution, and authigenesis of clays (dominantly kaolinite, mixed illite-smectite and minor illite). Mixed illite-smectite and illite occur as pore-filling and or lining during authigenic phases. Kaolinite and silica (quartz) overgrowth occur as pore-filling and lining cements. Compaction played an added role than the cementation in modifying the primary porosity. Cementation drastically reduced the porosity and permeability. Kaolinite fills pore spaces and caused reduction in the porosity and permeability of the sandstone. Secondary porosity development occurred due to partial to complete dissolution of feldspar. The diagenetic signatures observed in the Upper Kaimur Subgroup Sandstones are suggestive of intermediate burial (2-3 km depth). The reservoir quality of the studied sandstones is reduced by authigenic clay minerals (kaolinite, mixed illite-smectite and minor illite), cementations, and on other hand, it is increased by alteration and dissolution of unstable grains.