Sedimentology and reservoir characterisation of Lower Jurassic clastic sedimentary rocks, Salt and Trans Indus Ranges, Pakistan: Evidence from petrography, scanning electron microscopy and petrophysics

Abstract

In this study, sandstones of the Lower Jurassic Datta Formation in the Salt and Trans-Indus ranges are investigated regarding composition, diagenesis, provenance and reservoir properties using petrography, scanning electron microscopy and petrophysical analysis. The detrital mineral composition of the Datta Formation indicated that the sandstones are quartzose, lithic-quartzose, lithic-feldspatho-quartzose, lithic-quartzo-feldspathic, quartzo-lithic and feldspatho-quartzose, primarily from the recycled orogen setting, including the Malani Igneous Suite, the Aravali Range and Nagar Parkar. The Datta Formation has sub-angular to well-rounded, fine to coarse and moderate to well-sorted grains. Numerous diagnostic processes that occurred in the early to late stages of diagenesis, such as compaction, pressure solution, cementation, alteration, dolomitisation and dissolution, are supported by evidence in the Datta Formation. Dissolution, physical compaction, dolomitisation and alteration enhanced the reservoir quality, while pressure solution and cementation reduced the reservoir quality of the Datta Formation. The porosity types detected in the Datta Formation under scanning electron microscopy are vuggy, intracrystalline/intraparticle, dissolution and intercrystalline, with an average petrographic visual porosity of 11%. The petrophysical aspects of the Datta Formation in the Chonai-01 well and the correlation between four wells indicated that the hydrocarbons had shifted up-dip towards the Isa-Khail-01 well, so it is recommended for drilling because of the greater depositional thickness. The comparison of the Datta Formation with age-equivalent units in other regions of eastern Tethys provided a better understanding of reservoir heterogeneities that can be applicable in areas with similar geological conditions for future petroleum exploration.