Core Laboratories

The middle-late Permian was an interval with global paleoenvironmental and paleoeceanographic instabilities, including the end-Guadalupian or the Guadlupian-Lopingian major extinction event. It was controlled by massive eruptions of the Emeishan Large Igneous Province (LIP) in South China, leading to the release of significant quantities of greenhouse gases and toxic elements into the ocean-atmosphere ecosystem. Here, the middle-upper Permian strata at the Xibeixiang section and well Daye 1 (DY1) from the western and northern depression of the Sichuan Basin were analyzed for palynological data, total organic carbon (TOC), Rock-Eval pyrolysis, and organic petrography. The identified palynomorphs are dominated by significantly high concentrations of acritarch, mainly of Leiosphaeridia and Lophosphaeridium, along with moderate to low abundances of prasinophytes, mainly Dictyotidium with some Cymatiosphaera. These palynomorphs reflect deposition of the Gufeng and Wujiaping formations in a shallow marine shelf environment characterized by low-energy and reducing conditions, consistent with occasional occurrences of foraminiferal test linings, pollen, and spores. Elevated levels of phytoclasts and sparse spores and pollen in the Gufeng Formation reinforce high terrestrial influx, compared to low phytoclasts and absence of terrestrial palynomorphs in the Wujiaping Formation, which indicated low-energy, distal depositional conditions associated with subsidence of the Guangwang-Kaijiang-Liangping Trough. Source rock evaluation revealed fair to excellent organic matter richness in the Gufeng Formation, compared to poor to very good richness in the Wujiaping Formation. However, both formations exhibited poor present-day hydrocarbon generation potential of Type III-IV kerogen, with most samples have reached the dry gas stage. The back-calculated (original) S2o and HIo values revealed good to excellent generative potential and Type II to mixed Type II/III kerogen. In the study region, the eruption of the Emeishan LIP resulted in high rates of greenhouse outgasing and isotopically light carbon resulting in global perturbations in the carbon cycle, elevated organic carbon export, and the development of anoxic-euxinic conditions as evidenced from framboidal pyrite size and redox-sensitive elements. Additionally, it controlled a spike in heat flow patterns throughout the Sichuan Basin and thus expedited the thermal evolution of organic matter. As a consequence, the Permian source rocks in the Sichuan Basin entered the peak oil window in the Early Triassic, while they reached the dry gas window by the Jurassic.

Despite widespread organic-rich accumulations in southern Tethyan basins during the Late Cretaceous greenhouse, the relative role of climate-derived weathering, redox regime, paleoproductivity, and regional tectonics in controlling organic matter enrichment and preservation remains poorly constrained. This work investigates how these interacting geological processes governed organic matter richness and redox evolution in Campanian-Maastrichtian strata of the Abu Tartur Plateau, Dakhla Basin (southern Western Desert, Egypt). The study combined bulk-rock elemental and organic geochemical and sedimentological data from phosphates, black and gray shales, limestones, and glauconites of the Phosphate, Liffiya Shale, and Maghrabi Shale members of the Duwi Formation and the overlying Dakhla Formation. Chemical index of alteration (CIA), C-value and other elemental proxies revealed deposition under predominant humid climates and intense continental weathering, interrupted by short-lived arid-semi-arid to semi-humid intervals, corresponding to the development of phosphorite and carbonate beds. These climatic and weathering trends coincide with coeval intervals from the Red Sea and Nile Valley, reflecting the regional geological processes at the near-equatorial southern Tethyan margin during the Campanian-Maastrichtian. Source rock characterization indicates poor to very good with a few intervals of excellent organic matter richness and kerogen Type III with minor Type II. The deposition of the Duwi and Dakhla formations was concurrent with episodic subsidence versus uplift of the Gilf El-Kebir spur and Nubian Swell, consistent with sea-level rise and increased accommodation space and induced upwelling in open shelf settings of the southern Tethys. These conditions governed O2 replenishment faster than consumption leading to oxic-suboxic environments dominated by organic-rich deposits via organic matter production under enhanced upwelling than persistent anoxia. Conversely, black shales of the Maghrabi Shale Member were deposited under anoxic settings accompanied by elevated biological productivity. Preferential Mo enrichments in black shales compared to limited enrichments of other redox-sensitive metals suggest the operation of a particulate shuttle during short-term redox fluctuations. The mechanism behind enhanced anoxia included episodes of relative sea-level fall and decreased accommodation space along with regional tectonic uplift of adjacent uplands, resulting in a semi-enclosed basin with restricted circulation that promoted nutrient supply and oxygen depletion, favorable for organic matter preservation. The Dakhla Formation was deposited in similar marine environmental conditions to the Liffiya Shale Member; however, intensified weathering and associated terrigenous supply versus limited biological productivity and well-ventilated water column resulted in a strong dilution of labile organic matter and deposition of organic carbon-lean shales.

This study investigates the hydrocarbon source-rock potential of the late Paleozoic Nubia Sandstone in the Gulf of Suez, Egypt, using an integrated palynological, palynofacies, petrographic, and organic geochemical approach. Subsurface samples were collected from multiple wells in the July and October oil fields. Palynological analysis constrains the age of the Nubia Sandstone to the lowermost Carboniferous in the July Field and to the Permo-Carboniferous in the October Field. Palynofacies characteristics indicate contrasting depositional environments between the two fields. The October Field sediments were deposited under suboxic to anoxic marine conditions that favored the preservation of organic matter. In contrast, the July Field reflects a more proximal, oxic shelf environment dominated by terrestrial organic input. This study presents the first integrated organic geochemical evaluation of Paleozoic Nubia Sandstone source rocks in the Gulf of Suez. Newly generated and previously unpublished geochemical data from multiple wells have been analyzed. These data provide important insights into the distribution, quality, and hydrocarbon generation potential of Carboniferous organic-rich siliciclastic successions. The findings highlight their significance as underexplored exploration targets in North Africa.

The petroleum system in the Risha gas field, eastern Jordan, is not fully understood. The current study aims to evaluate source rocks, reservoirs, and seals within the basin by integrating 1D basin models and well logs together with geochemical and petrophysical data. Two effective source rocks are identified within the Paleozoic shale intervals, namely the Mudawwara and Dubeidib formations. The Mudawwara and Dubeidib formations with TOC values ranging from 0.51 to 6.75 wt%, which suggests poor to very good potential. The formations contain primarily Type III (gas-prone) and mixed Type II/III (oil/gas-prone) kerogen. The thickness of the Paleozoic sedimentary section increases to the east. In contrast, the thickness of the Mesozoic section increases to the west, and the entrapment area in the middle to the eastern part of the study area is characterized by the accumulation of petroleum in the Ordovician sandstone reservoirs. The Risha sandstone reservoir has an increased net pay thickness in east and southeast directions. The migration of hydrocarbons petroleum in the Risha gas field is strongly suggested as a direct primary migration from the source rock intervals within the Mudawwara and Dubeidib shales to the intercalated sandstone reservoirs of the Risah and Dubeidib formations. In addition, vertical migration along faults and up-dip migration to the middle and eastern parts of the study area are also suggested. The Risha-14 well represents the ideal petroleum system in eastern Jordan, as it encompasses all the key elements of petroleum generation and accumulation. The critical moment for the source rock is estimated to have occurred approximately 250 Ma ago. The effective shale source rocks of the Mudawwara Formation were deposited in the Early Silurian. They entered the main oil window in the Early Devonian (similar to 410 Ma ago), with significant gas generation occurring in the early Carboniferous (similar to 330 Ma ago). The Dubeidib Formation sandstone reservoir was deposited during the Ordovician (485-458 Ma ago). Structural traps formed during the Paleozoic (280-250 Ma ago), formed during the Hercynian Orogeny through rifting and compression phases were subsequently charged with petroleum through migration and accumulation.

The mountainous landscapes of southwest China are renowned for their complex geological settings, a region where an extensive network of tunnels, including railway to highway and hydraulic engineering tunnels, is planned for construction. The area has witnessed several severe incidents resulting in casualties caused by underground harmful gases during tunnelling activities. With ongoing development, it is critical to investigate the risks associated with harmful gases in tunnelling projects within the region. Current research on the formation and enrichment mechanisms of harmful gases remains insufficient. This study investigates the relationship between harmful gases and the geological structures and strata by conducting through geological surveys, sampling tests, field observations, and employing advanced geological forecasting in both surveyed areas and existing tunnels. The findings identified three main mechanisms for the generation of harmful gases: hydrocarbon generation, thermochemical reactions, and hydrothermal migration. Methane, carbon dioxide, carbon monoxide, and hydrogen sulfide are the predominant gases encountered during tunnel construction. These harmful gases tend to migrate upwards, with their migration distance and rate of diffusion were controlled by faults and/or fractures. This migration can lead to localized accumulations of harmful gases, which we categorized as fault-controlled and joint-controlled accumulation types. This study interprets the disaster-causing mechanisms of harmful gases, suggesting that risk identification and advanced forecasting methods of tunnel harmful gases establish classification criteria for assessing gas risks during construction, and forms a comprehensive risk management system spanning the entire process from investigation, design, to construction. Future research directions should focus on the application of artificial intelligence for predicting harmful gas risks, the management of high-pressure gases in tunnels exceeding 1000 m in depth, and the development of strategies to mitigate the toxicity of harmful gases. These findings offer a theoretical basis and technical guidance for the safe construction of tunnels.