Abstract
Petrologic investigations of the sixty representative thin sections from the Pab Formation within Rakhi Gorge section Eastern Sulaiman Range Pakistan have been used to characterize different diagenetic patterns, identification of primary composition and reservoir characters. Sublithic, lithic and quartzose sandstones have been the principal constituents of the formation. The processes responsible for the late-stage alteration and diagenetic processes identified during the petrographic study include compaction of lithic fragments and mud clasts, formation of quartz overgrowth structures, feldspar replacement and alteration, cementation, and replacement of grains by clay minerals other ferrous elements and diagenetic minerals. The study shows that the initial porosity has been primary intergranular, but the secondary porosity has been originated in the rocks as a result of the alteration of the primary and secondary constituents, as well as fracturing. These facies characters replicate the reservoir quality including, good, medium, low-quality, and non-reservoir. Samples displaying average total porosity greater than 10 % have been declared as good quality. While rocks samples having 7 % or greater porosity are grouped as a medium reservoir. Those samples consisting of porosity values between 1 and 4% are considered as a low quality reservoir while those samples having porosity ranges low than 1% have been called non-reservoir. Based on the investigated parameters the studied samples from the Pab Formation displayed the characters of a medium reservoir that may hold significant hydrocarbon. This different quality including good and low quality zonation can be attributed to the facies and diagenetic change in the formation.
Highlights
Sandstone reservoir rocks have been studied by different authors (Ahmad et al, 2020) concerning its hydrocarbon potential and the processes responsible for the generation of porosity
Clastic deposits of the Cretaceous Pab Formation have been considered as important hydrocarbon reservoirs in south-west Pakistan (Sultan & Gipson, 1995; Beswetherick & Bokhari, 2000; Hedley et al, 2001)
In Pakistan a lot of work has been carried out in the field of sedimentology and stratigraphy petrographic studies focusing on reservoir properties in different basins are not enough, and the Middle Indus Basin is not an exception (Qureshi et al, 1996)
Summary
Sandstone reservoir rocks have been studied by different authors (Ahmad et al, 2020) concerning its hydrocarbon potential and the processes responsible for the generation of porosity. Pab Formation in different geographic locations has been focused by different authors on the regional stratigraphic architecture, sedimentology, and interpretation of depositional systems (Eschard et al, 2002). These studies are important in terms of understanding the macroscopic reservoir and textural characters of reservoir potentials. Diagenetic alteration and understanding the processes that govern the reservoir quality are very important in the interpretation of a reservoir for its hydrocarbon potential (Bloch & Helmold, 1995; Morad et al, 2000; Ketzer et al, 2003).
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