Impact of sedimentary environment on pore parameters of thermally mature Permian shale: A study from Kommugudem Formation of Krishna Godavari Basin, India

The pores are significant factors to assess the fracture system of a shale reservoir. The present study evaluates organic matter-associated parameters, redox condition, paleoclimate and paleosalinity and their role on the pore structure of thermally mature Kommugudem shale of Krishna Godavari Basin. The XRD analysis supported by FESEM mainly indicates silica-dominated lithotype and clay-rich siliceous mudstone in the Kommugudem Formation. Intercrystalline and intracrystalline pores were observed in association with mineral and organic matter that provide storage sites for hydrocarbon. Excellent TOC content and genesis of gas prone, type III kerogen dominantly observed in admixture with type II or type IV kerogen. The clay, TOC and Tmax have a positive correlation with micropore volume indicating a good contribution of clay micropore and associated organic matter. Fractal dimensions were estimated using the fractal FHH method with an average value of 2.65 suggesting that the pore surfaces are rough and exhibit complex and heterogeneous pore structure. The Kommugudem Formation constitutes detrital sediments sourced from felsic volcanic rocks in humid and warm climate along the passive tectonic continental margin. The redox and paleosaline investigations reveal the fluvio-marine transitional environment preserved under suboxic to oxic conditions. The REEs and trace elements are positively correlated with pore volume indicating their possible role in the pore genesis of silicate minerals and corroborating the positive influence of the environment. The redox proxies are strongly correlated with TOC and pore volume supports the probable development of organopores. The investigation reveals the significant role of multiproxy paleoenvironmental indices to understand the complex mechanism of pore characteristics.