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The Albian–Aptian Goru Formation represents a fluvio-deltaic reservoir in both the Central and Southern Indus Basin, Pakistan. Using high-resolution core data, this study provides comprehensive insights into the depositional environment and its role in influencing reservoir heterogeneities in the studied formation. The sedimentological investigations demonstrate five lithofacies, namely, (i) massive sandstone (Sm), (ii) horizontal to low-angle planar laminated sandstone (Sl), (iii) planar cross-laminated sandstone (Sc), (iv) heterolithic beds (Hw and Hr), and (v) massive mudstone (Mm). Facies associations reflect shallow marine depositional settings varying from deltaic in the NE to strand plain in the SW. The framework grains of the established lithofacies exhibit quartzo-feldspathic petrofabrics, which have been sourced from stable craton-continental block settings. The petrophysical data in the core depth zone show high shale content in Well-A and lower parts of Well-B. In Well-A, the crossover between the density and neutron logs is not observed, which suggests unsaturated sands, while Well-B exhibits a permeable zone as indicated by neutron-density crossover, low gamma ray values, and relatively high porosity. The petrographic analysis and scanning electron microscopy indicate high effective porosities contributed by both primary (intergranular and intercrystalline) and secondary porosity (owing to fracturing and dissolution). The upper part of Well-B shows high porosity values up to 28% due to highly fractured quartz. Porosity values are low in the lower parts of the Well-A and Well-B due to intensive calcite cementation, chlorite recrystallization, proto matrix as well as pseudo matrix. This suggests that both Well-A and Well-B have a common source but the reservoir properties can be attributed to the depositional and post-depositional variations in the petrofabric of the studied lithological units. The Cretaceous Goru Formation in Southern Indus Basin, the Pariwar formations in Jaisalmar Basin, and Bhuj Formation in Kutch Basin share same geological history and sedimentary processes. Thus, these studies can be utilized in the exploration of Cretaceous reservoirs in these basins. [ABSTRACT FROM AUTHOR]

This research article presents a comprehensive work on sedimentological study of the Yamama Formation in the Saudi Arabia, aiming to enhance understanding of its depositional environments, diagenetic evolution, and reservoir properties of the formation. Integrated field and petrographic studies are used to interpret microfacies, depositional environment and diagenetic history of the Yamama Formation near Riyadh, Saudi Arabia. Field investigations show that the formation is thin- to thick-bedded, massive to nodular limestone with small patches of shale and marl. Petrographic studies show four distinct microfacies, i.e., mudstone MF-I, wackestone MF-II, packstone MF-III, grainstone MF-IV. The microfacies and their associations represent homoclinal ramp depositional setting designated on the basis of the relative percentage of allochems and orthochems. The diagenetic history, which includes eogenetic, mesogenetic, and telogenetic stages, is discussed as follows: The eogenetic stage includes burrowing, micrtization, neomorphism, and drusy mosaic cementation; the mesogenetic stage includes compaction (mechanical and chemical) and dissolution. The telogenetic stage is evident from calcite-filled fracture veins crosscutting the rock unit. The reservoir properties are directly dependent on both depositional and diagenetic processes. The reservoir quality of the formation has been significantly reduced by the precipitation of different types of cements during the diagenetic processes, as observed in the detailed paragentic sequence; however, during the late stage, fracturing has enhanced the reservoir quality significantly during the late stage. [ABSTRACT FROM AUTHOR]

The middle Jurassic Samana Suk Formation is well exposed in Himalayan foreland fold and thrust belt forming a good hydrocarbon reservoir of the Indus Basin; however, the combined sedimentological and geochemical studies are not conducted so far. An integrated approach using field, petrographic, geochemical, and isotopic studies was used to better understand the depositional and diagenetic processes within the formation. The formation is predominantly composed of thin to medium-bedded limestone with intercalation of shale. Field observations reveal sedimentary and diagenetic features such as cross bedding, sole marks, ripple marks, convolute bedding, stylolites, dissolution marks and patchy dolomitization. Microfacies associations include mudflat microfacies associations (mudstone MF-1, dolo-mudstone MF-2), lagoonal microfacies associations (siliciclastic bio-packstone MF-3, peloidal bioclastic packstone MF-4, bioclastic wackestone MF-5, and peloidal wackestone MF-6), barrier/shoal microfacies association (peloidal grainstone MF-7, ooidal–peloidal bioclastic grainstone MF-8, ooidal grainstone MF-9, and bioclastic peloidal grainstone MF-10). The above-mentioned microfacies associations suggest the deposition in the ramp settings (mudflats, lagoonal and shoal). The diagenetic features include: micritization, mechanical/chemical compaction, dissolution, neomorphism, cementation, dolomitization and fracturing. Selective replacement of grain dominated facies represents fabric retentive replacive dolomite RD-I formed at the early phase, followed by matrix replacive dolomite RD-II. Late-stage diagenetic alteration is marked by fabric-destructive dolomite RD-III. Geochemical data show a consistent decrease in salinity from the early to late diagenetic phases characterized by elevated Na and K concentration and reduced Fe and Mn concentration. Furthermore, stable isotopic data of limestone and dolomite phases show non-depleted δ13 C values ranging from + 0.26 to + 1.86‰ VPDB suggesting no external supply of carbon after the deposition of the carbonate units. The non-depleted δ18 O values ranging from − 1.96 to − 0.45‰ VPDB of dolomite phases represents seawater signatures, and hence may have formed in surface processes of marine water in mudflat settings/evaporitic conditions. Paleogeographically, Samana Suk Formation exhibits similar depositional conditions with the western coastline of the Tethys. [ABSTRACT FROM AUTHOR]