Reservoir potential of middle Jurassic carbonates in the Nizampur Basin, Pakistan: Insights from paleoenvironmental and diagenetic analyses

Abstract

Depositional and diagenetic processes are the primary controls that impact the quality of carbonate reservoirs. The findings of a multiproxy study on carbonates of the Middle Jurassic Samana Suk Formation from the Nizampur Basin of Pakistan display a wide range of rock fabrics and diagenetic features, all affecting reservoir potential and flow properties in a complex manner. Based on petrographic and facies analyses, the model of a homoclinal ramp geometry with four characteristic microfacies types is proposed, including bioclastic mudstone, bioclastic wackestone, peloidal packstone, and bioclastic peloidal grainstone deposited in shoals, lagoons (restricted and relatively open conditions), and open marine environments. The Samana Suk Formation reservoir properties are shaped by diagenetic processes reflecting marine, meteoric, and burial diagenetic settings, such as the porosity being enhanced by fracturing, dolomitization, and dissolution, while cementation, chemical compaction, micritization, and neomorphism have reduced it. The 3-D microporosity in the form of vugs, intergranular, intercrystalline, and intraparticle pore spaces was unveiled through scanning electron microscopy (SEM). The net porosity of the formation could be enhanced by dissolution and fracturing, which makes it a better reservoir for petroleum exploration. The data shown here has been correlated with its nearby stratigraphic equivalents dealing with the Jumara Dome sediments of the Kachchh Basin and the Jaisalmer Formation (Fort Member) of the Jaisalmer Basin on India's western margin, which is important to understand and predict reservoir properties in other carbonate fields with similar properties.