Hossain Rahimpour-Bonab

Marine environmental conditions govern carbonate sediment types through their influence on carbonate factories. These factories, the sites of carbonate production, adjust to environmental shifts by altering precipitation forms. This study examines Permian-Triassic strata in the Persian Gulf to understand how environmental changes, particularly a major biocrisis, impacted carbonate sedimentation. Thin section analysis, core data, and gamma-ray logs were utilised to reconstruct this history. During the late Permian, a thriving tropical carbonate factory was established along the Neo-Tethys margin. Favourable environmental conditions and ample accommodation space facilitated its expansion and fostered the proliferation of diverse marine life. The Dalan Formation, characterised by grain-dominated facies, resulted, with peloids, ooids, and skeletal fragments making up the bulk of the sediment. Carbonate production was driven by both chemical precipitation and metazoan activity. The Permian-Triassic boundary extinction event profoundly impacted sedimentation. Metazoans nearly disappeared, creating a ‘Barzakh condition’ (microbial dominated system) in the Early Triassic, in which microbial populations were no longer suppressed by metazoan predators. Increased calcium carbonate saturation and nutrient levels, likely due to upwelling and consumer removal, favoured microbial carbonate factories. Consequently, the Lower Triassic succession in the Persian Gulf exhibits a clear shift towards microbial-mediated carbonate sediments. This study is significant due to its focus on shallow marine settings along the Arabian Plate, demonstrating how Earth system events, particularly the end-Permian mass extinction, fundamentally altered carbonate platform production and dynamics. These environmental changes also impacted reservoir properties, which are relevant for understanding the region's hydrocarbon resources.

Marine environmental conditions govern carbonate sediment types through their influence on carbonate factories. These factories, the sites of carbonate production, adjust to environmental shifts by altering precipitation forms. This study examines Permian-Triassic strata in the Persian Gulf to understand how environmental changes, particularly a major biocrisis, impacted carbonate sedimentation. Thin section analysis, core data, and gamma-ray logs were utilized to reconstruct this history. During the Late Permian, a thriving tropical carbonate factory was established along the Neo-Tethys margin. Favorable environmental conditions and ample accommodation space facilitated its expansion and fostered the proliferation of diverse marine life. The Dalan Formation, characterized by grain-dominated facies, resulted, with peloids, ooids, and skeletal fragments making up the bulk of the sediment. Carbonate production was driven by both chemical precipitation and metazoan activity. The Permian-Triassic boundary extinction event profoundly impacted sedimentation. Metazoan disappearance created a ‘Barzakh condition’ in the Early Triassic, where microbial populations were no longer suppressed by metazoan predators. Increased calcium carbonate saturation and nutrient levels, likely due to upwelling and consumer removal, favored microbial carbonate factories. Consequently, the Early Triassic succession in the Persian Gulf exhibits a clear shift towards microbial-mediated carbonate sediments. This study is significant due to its focus on shallow marine settings along the Arabian Plate, a region rich in hydrocarbon reservoirs. Carbonate factory dynamics, influenced by environmental changes, impacted reservoir properties, crucial for reservoir management and development

This study examines the bulk organic geochemical properties, the burial and thermal history reconstruction, and timing of hydrocarbon generation of Jurassic and Cretaceous source rocks in the Abadan Plain, within the western Zagros fold‐and‐thrust belt in SW Iran. Three source rock units were evaluated: the Middle Jurassic (Bajocian–Callovian) Sargelu Formation, the Lower Cretaceous (Neocomian) Garau Formation, and the Lower Cretaceous (Aptian–Albian) Kazhdumi Formation. Rock‐Eval pyrolysis and organic petrography analyses revealed that the Sargelu Formation is overmature, with abundant solid bitumen and pyrobitumen, indicating depleted hydrocarbon generation potential. Total organic carbon (TOC) values range from 0.46 to 14.8 wt% with low hydrogen index (HI) values, suggesting no further liquid hydrocarbon generation is possible. The Garau Formation is highly mature with TOC values of 0.44–9.4 wt% and HI values below 400 mg HC/g TOC, confirming that hydrocarbon generation has occurred. While the advanced maturity of both formations prevents direct kerogen‐type identification through Rock‐Eval results, petrography indicates the Sargelu and Garau formations are indicative of Type II kerogen. The Kazhdumi Formation shows varied maturity levels, ranging from immature to marginally mature, with TOC values between 0.16 and 6.33 wt% and HI values from 72 to 626 mg HC/g TOC, reflecting a mix of Types II and III kerogen.The one‐/two‐dimensional basin modeling conducted across the Azadegan, Yadavaran, Darquain, and Mahshahr fields reveals significant variations in burial depth, thermal history, and hydrocarbon generation potential. Thermal modeling indicates maximum burial temperatures were reached in the late Neogene, with the basal heat flow value of 45 mW/m² for most fields, except in Darquain, where an elevated basal heat flow of 62 mW/m², potentially linked to detachment thrusting within the Hormuz salt caused by the reactivation of basement faults, accelerated thermal maturation of the Sargelu and Garau source rocks. In Darquain, the Sargelu Formation has entered the wet gas window (VRo% ∼1.9), and the Garau Formation. has reached late oil to wet gas maturity (VRo% ∼1.5), while in Azadegan both remain in the late oil window. The Kazhdumi Formation remains immature to marginally mature across all fields. The calculated transformation ratio (TR) shows that the Sargelu and Garau Formation. Source rocks in Darquain have surpassed 90% TR, fully exhausting their liquid hydrocarbon generation potential. These findings offer critical insights into the petroleum system of the Abadan Plain, highlighting areas like Darquain, where hydrocarbons have already been expelled and zones such as Azadegan and Mahshahr, with further oil generation potential.

Hydrocarbon reserves are commonly estimated from electrical logs based on the Archie’s law. Therefore, understanding the concepts and precise determination of Archie’s parameters play an essential role in reservoir studies. The electrical properties of carbonates are affected by both microstructures and wetting characteristics of these heterogeneous rocks. Understanding of these effects and prediction of Archie’s parameters are significant theoretical and experimental challenges. In this paper, these effects were analyzed separately using rocks with various lithologies including limestone, dolomitic limestone and dolostones. Samples with different sedimentary textures (grainstones and packstones), porosities and pore types were also considered under different laboratory conditions. For microstructure effects analysis, 16 heterogeneous carbonate samples having a wide range of microstructures were selected. To decrease wetting effect, the washed samples were tested in air–brine injection system at ambient conditions to measure saturation exponent. Subsequently, in order to investigate the influence of the wetting characteristics on this exponent, 25 homogeneous limestone samples were employed for water–oil injection under reservoir conditions. The porous plate was used as a standard technique to determine the saturation exponent as an electrical index. The results showed that pore connectivity and wettability are the main factors affecting the saturation exponent. Heterogeneity, including the presence of large pores and bimodal texture, is another effective factor that complicates the relationship between saturation exponent and wettability. Furthermore, results indicate variation of the saturation exponent with fluid saturation. Finally, equations were obtained to interpret and calculate the saturation exponent using capillary pressure data by mercury injection method. The derived equations clearly demonstrate the significant impact of the studied parameters on the saturation exponent in carbonate rocks.

Peat forming environment strongly influences the economic value of any coal seam and coal-bearing strata. Hence, palaeoenvironmental studies provide important information for coal resource exploration. In this context, detailed studies on selected coals from the Parvadeh Area, Iran, were conducted using sedimentology, coal petrology, X-ray diffraction (XRD), scanning electron microscopy- energy dispersive X-ray analyzer (SEM-EDX), and proximate analysis. The sedimentary facies above and below the coal seams are mainly marine or marine-influenced facies, supporting that the coal-forming mires in the Parvadeh Area developed in a paralic environment, where the base level must be closely related to sea level. Sulfur contents are moderate to high and mark the influence of brackish/marine water, especially during transgression after peat growth in a lower delta plain environment. The peat-forming mires extended on coastal/delta plain lobes. The lower delta plain/coastal plain coals are characterized by lateral continuity and substantial thickness, whereas few coals possibly representing the upper delta plain are thin and more discontinuous. The detrital nature and composition of the numerous partings and the overall high ash yield in the coal seams indicate an active tectonic area with high rates of creation of accommodation space over peat growth. Coal petrology and coal facies analysis exhibits a permanently high water table within a forest swamp and mostly rheotrophic conditions, sometimes with connection to the seawater. According to paleoenvironmental reconstructions, it seems that coal layers may be thicker, with less sulfur (pyrite), but more clastic minerals and partings toward the western part of the area. Although these coal seams presently have low economic potential for the mining operation, partly due to great depth, this humic, high-volatile to medium-volatile bituminous coal may be suitable for exploration of coal bed methane resources.