Investigating the impact of diagenesis on reservoir quality of the Jurassic shallow shelfal carbonate deposits: Kala Chitta Range, North Pakistan

The Middle Jurassic carbonate succession (Samana Suk Formation) in Kala Chitta Range, North Pakistan was studied in detail to investigate the impact of diagenesis on reservoir potential of the rock unit. The current study integrates detailed geological field, petrographic, scanning electron microscopic, and advance geochemical studies to reconstruct the diagenetic history of Jurassic carbonates and to evaluate its role in re‐shaping the reservoir potential. Based on field observations, five lithological units along with diagenetic features are recorded. Furthermore, various microfacies are defined within each lithological unit. Based on petrographic studies, it is observed that various diagenetic features including micritization, neomorphism, dissolution, compaction (mechanical and chemical), dolomitization, and cementation have played a crucial role in the porosity modification of various lithological units. The paragenetic sequence established in this study reveals modification of the carbonates in various diagenetic phases, for example, marine, meteoric, and burial (shallow and deep) diagenesis, followed by a phase of uplifting. Based on different types of microscopic porosities generated during various diagenetic phases, mudstone to wackestone carries good reservoir potential while the grainstone has moderate to poor potential. The plug porosity and permeability data further corroborate these findings. At outcrop, various large‐scale dissolution activities and dense network of inter‐connected fractures in all lithological units may have further enhanced the reservoir potential of the studied strata. The detailed integrated studies of Jurassic carbonates show that diagenesis has greatly modified the rock unit in the different diagenetic environments. Such diagenetic alterations have both positive/negative impacts on reshaping the reservoir potential.