Reservoir characterization and rock eval pyrolysis of clastic sedimentary rocks in the Geku Formation, Arunachal Pradesh, North-eastern India

Abstract

The present investigation aims to decipher the reservoir quality and source rock potential of the sandstones and shales of the Geku Formation of the Yinkiong Group, Eastern Himalaya, NE India. To achieve the goal, sandstone petrography and rock-eval pyrolysis of shale aided with X-Ray diffraction have been employed. A petrographic study revealed that the detrital constituent of the sandstones is mainly quartz, feldspar, and lithic fragments. Authigenic cements such as carbonate and clay bind the detrital materials as indicated by petrographic as well as X-Ray diffraction study. Clay minerals include illite, smectite-montmorillonite and kaolinite. The studied sandstones underwent compaction as evidenced by the formation of concavo-convex and sutured grain contacts, which also suggest its phyllomorphic stage of diagenesis. The presence of calcite and clay cement has led to reduction of the porosity and permeability of sandstones, which is also substantiated by sorting and irregular grain shapes such as sub-angular, angular, and sub-rounded, thereby affecting reservoir quality. The rock eval pyrolysis data suggests that the Yinkiong shales have poor source rock potential with dominantly kerogen type III. The geochemical parameters of the studied shales suggest mostly immature and postmature organic matter and the very low TOC values indicate poor organic richness.