No abstract

In Pakistan, carbonate rocks of Jurassic age are present entirely throughout the Indus Basin. The Jurassic carbonate rocks present in the Attock-Cherat requires a more detailed investigation as of recent discovery of gas in Jurassic carbonate rocks in the lower Indus basin. The evaluation of these Jurassic carbonate units in the Nizampur Basin of Attock-Cherat ranges should integrate the aspects of the depositional sediments, diagenetic history, and geochemistry to understand the reservoir behavior. In this study, the Samanasuk Formation of 90 m was sampled and measured in detail, and samples were collected with ~ 0.3 m interval and some samples were collected where reckoned necessary. Petrographic and microfacies analysis were conducted on about 100 samples; moreover, XRD analysis were performed. The present study aims to determine the depositional facies, diagenetic processes, and geochemical elements of this carbonate succession of the in an effort to explore their effect on reservoir quality. The Samanasuk Formation comprises eight microfacies assigning three facies belts including peritidal, lagoon, and shoal of a carbonate ramp. The recorded diagenetic processes include dolomitization, compaction, micritization, neomorphism, dissolution, and cementation in which dolomitization played an important role in enhancing the reservoir quality. In relation of their impacts on reservoir properties, the grainstone facies associated with peritidal facies and dolomudstone facie associated with carbonate sand and shoal shows the greatest reservoir quality, whereas lagoonal facies has the lowest reservoir quality. This study represents an approach to use the depositional facies, diagenetic alterations, and geochemical framework of carbonate succession in the reservoir characterization.

An integrated study of sediments was conducted to examine the facies architecture and depositional environment of the Cretaceous Pab Formation, Rakhi Gorge, and Suleiman Ranges, Pakistan. This research focused on analyzing architectural elements and facies, which are not commonly studied in sedimentary basins in Pakistan. To identify lithofacies, outcrop analysis and section measurement were performed. The identified lithofacies were then categorized based on their depositional characteristics and facies associations, with a total of nine types identified within a stratigraphic thickness of approximately 480 m. These facies were mainly indicative of high-energy environments, although the specifics varied by location. Sedimentary structures such as planar and trough crossbedding, lamination, nodularity, load-casts, and fossil traces were found within these facies, indicating high-energy environments with a few exceptions in calm environments. The identified facies were grouped into seven architectural elements according to their depositional environments: delta-dominated elements, including laminated shale sheet elements (LS), fine sandstone elements (SF), planar cross-bedded sandstone elements (SCp), trace sandstone elements (ST), and paleosol elements (Pa); and river-dominated elements, including trough cross-bedded sandstone elements (SCt), channel deposit elements (CH), and paleosol elements (Pa). These architectural elements, along with their vertical and lateral relationships, indicate a transitional fluvio-deltaic environment within the Pab Formation. In conclusion, by interpreting facies and architectural elements, it is possible to gain a better understanding of the depositional history of the formation and the distribution of reservoir units.

No abstract