Integrated sedimentary and diagenetic constraints for delineating the reservoir potential of Jurassic carbonate sequences in the autochthonous Samana Suk Formation, Attock-Cherat Nizampur Area, Pakistan

Abstract

In the geology of Pakistan, the Jurassic carbonate sequence is widely spread around the Upper Indus Basin periphery. Specifically, the indigenous Jurassic layers within the carbonate framework, known as the Samana Suk Formation, situated in the Kahi section Nizampur area, necessitate an extensive examination for future exploration. This investigation is prompted by the recent gas discovery in Jurassic carbonate rocks in the lower Indus Basin, indicating their potential as reservoirs. A thorough evaluation of these Jurassic carbonate units, specifically the Samana Suk Formation, within the Nizampur Basin of the Attock-Cherat ranges, involves a multifaceted approach encompassing observational aspects such as depositional history and diagenetic transformations. Field samples were collected from selected Dolomite beds, and a sedimentological analysis was performed on 20 samples. The current study of the Samana Suk Formation provides a detailed account of diagenetic alterations, delineating various variations in depositional environments represented as different facies: KS-1 Dolomitic Grainstone, KS-2 Bioclastic Wackstone-Mudstone, and KS-3 Bioclastic Peloidal Wackstone. The primary objective is to ascertain the paragenetic sequence of the carbonate succession concerning reservoir quality. The identified diagenetic processes encompass dolomitization, fluid circulation patterns, compaction, micritization, dissolution, and cementation. Notably, dolomitization significantly contributes to enhancing reservoir quality generally and about 50% of the whole world’s carbonate reservoirs are in dolomite. This study significantly enhances our capacity to comprehend the broader spectrum of depositional facies and diagenetic changes within the carbonate succession, thereby shedding light on their reservoir potential.