Wentong He

Water blocking severely restricts gas mobility in tight sandstone reservoirs because of capillary-dominated retention of aqueous phases within micro–nanopore systems. This study establishes an integrated experimental framework to quantify the full-process evolution of water blocking─from water invasion and entrapment to gas displacement and supercritical CO2 (SC–CO2) treatment. Vacuum-assisted water saturation, pressure-controlled N2 displacement, and SC–CO2 shut-in soaking experiments were conducted on tight sandstone cores, and multiscale characterization methods, including nuclear magnetic resonance (NMR), microcomputed tomography (micro-CT), powder X-ray diffraction (XRD), and thin-section casting, were used. The results show that water invasion follows a three-stage temporal pattern, with rapid initial imbibition causing most of the water-blocking damage. Conventional N2 displacement effectively removes mobile water from pore domains with NMR-equivalent radii larger than approximately 300 nm, but it fails to mobilize capillary-trapped water in smaller pore domains, yielding displacement efficiencies less than 40%. SC–CO2 shut-in soaking significantly alters the pore network through mineral dissolution, possible wettability-related changes, and enlargement of micro–nanothroat structures, leading to enhanced pore connectivity and reduced capillary resistance. Following SC–CO2 pretreatment, the N2 displacement efficiency increases to 50–70% and the effective porosity shows a 10–20% improvement. The combined SC–CO2–N2 approach has a strong potential for mitigating water blocking in ultratight formations and may provide an experimental basis for future field-scale optimization of gas recovery and CO2-assisted reservoir treatment.

Oil shale in situ conversion provides an important pathway for developing medium- to deep-buried, low-grade, and thin oil shale resources. Among the available approaches, the in situ conversion technology triggered by the topochemical reaction method, hereafter referred to as the TSA method, induces local oxidation reactions of pyrolysis residuals, fixed carbon, and reactive organic matter through preheating and oxygen-containing gas injection. The released in-formation heat then supports continued kerogen cracking and reaction-front propagation. This review summarizes the TSA method from a process-oriented perspective, linking reaction mechanisms, engineering controls, geochemical process identification, pilot tests, economic–environmental constraints, and scale-up evaluation. Existing studies indicate that the TSA method has formed a technical chain involving reaction initiation, heat/reaction-front propagation, oil and gas recovery, and process monitoring. Pilot tests provide evidence for operational feasibility, but not yet for full commercial feasibility. Thermal simulation results show that oil and gas generation and expulsion become significant above ~350 °C, and that 375–425 °C can be used as an important reference window for temperature control rather than a fixed optimum for all oil shale reservoirs. Geochemical indicators can provide complementary constraints for identifying reaction progress, especially when calibrated with produced oil and gas. Further development should focus on fracture-network control, heat-transfer enhancement, oxygen-supply regulation, multi-well coordination, equipment reliability, economic evaluation, groundwater protection, and CO₂ emission accounting. These issues are critical for advancing the TSA method toward larger-scale, low-carbon, and well-regulated application.

The impact of magmatic intrusions on the porosity and reservoir quality of sandstone formations remains insufficiently understood, particularly in the context of thermal effects across different temperature zones. Existing studies have primarily focused on general porosity trends, but the precise mechanisms through which heat from magmatic intrusions alters reservoir properties have not been fully elucidated. This study addresses this gap by investigating the thermal effects of magmatic intrusions on sandstone reservoirs in the BZ34–9 oil field, located in the Huanghekou Sag of the Bohai Bay Basin, and the outcrop of the Lishu Fault Depression in the Songliao Basin. Through a combination of field research, NMR (nuclear magnetic resonance), X-ray diffraction, and micro-CT, alongside thermal simulation models and high-temperature experiments, this research demonstrates that proximity to magmatic intrusions significantly reduces sandstone porosity. Specifically, porosity in a high-temperature zone (HTZ, 400–600 °C) decreases by 30–50%, while in a low-temperature zone (LTZ, normal temperatures to 400 °C), it decreases by 16–20%. Thermal simulations using three geological models (thick sandstone with lateral thermal effects, thin sandstone and mudstone interbedding, and vertical thermal effects) reveal that heat propagates more widely in sandstone-dominated strata and that temperature decay occurs rapidly with increasing distance from the intrusion. High-temperature experiments further show that mineral expansion and clay dehydration below 700 °C reduce porosity, while at temperatures around 900 °C, calcareous cement decomposes, leading to a sharp increase in porosity. However, temperatures exceeding 1200 °C cause rock melting and the formation of isolated bubbles that destroy reservoir connectivity. This study provides new insights into the thermal modification mechanisms in sandstone reservoirs, offering a theoretical framework for enhancing oil and gas exploration strategies. The findings have important implications for the development of oil fields affected by magmatic intrusions and can inform the exploration and management of the BZ34–9 oil field.

Quantifying the amount of sulfur (S) released by magmatic activity is very important to accurately assess the climate impact caused by volcanic activity, but it is challenging for pre-Quaternary magmatic activity. During the Aptian-Albian period, the Songliao Basin experienced intense volcanic activity, resulting in the formation of a large volume of volcanic rocks. Among them, the intermediate-acid volcanic rocks of the first member of the Yingcheng Formation were formed in the middle to late Aptian and are characterized by wide distribution and considerable thickness. In addition, the southeastern margin of the Songliao Basin offers excellent outcrop conditions. By detecting the compositions and contents of major and volatile elements in the primary melt inclusions, the melt inclusions are divided into three types according to the evolution stages by the CaO/Al₂O₃ ratio: Type I (primitive), Type II (relatively evolved) and Type III (most evolved), and Type III melt inclusions are used to replace the missing matrix glass in the parent rock. The aerosols formed by the sulfur release that estimated by the "petrological method" led to the temperature drop in the region, which is consistent with the KAp4 sea level decline event. The study area (5.02 km²) is only 0.019% of the area of the Songliao Basin (2.6 × 10⁴ km²), so the degassing amount of intermediate-acid magma in the first member of the Yingcheng Formation in the whole Songliao Basin was enormous. It is not common to replace matrix glass with melt inclusions that formed in late magmatic evolution, but this may provide a new idea for studying the degassing of pre-Quaternary magmatic activities.

Mastering the reaction process of underground pyrolysis is the key to oil shale in-situ conversion project. The progress of the pyrolysis reaction can be analyzed by the information of the kerogen maturity in the reaction formation. However, it is difficult to directly test the kerogen maturity by drilling and coring in in-situ conversion project. And the research on judging the process of underground pyrolysis reaction according to the maturity of oil and gas products has not been carried out in depth. This project intends to take the oil shale of the Nenjiang Formation in the southern Songliao Basin and the pyrolysis oil samples produced by the in-situ conversion project as the research object, and conduct simulation experiments and test analysis. The purpose of this paper is to identify the dynamic evolution characteristics of carbon isotope fractionation during the evolution of oil shale pyrolysis hydrocarbon products, and then establish the response relationship with the process of oil shale organic matter pyrolysis. This study has formed a set of dynamic monitoring methods for the in-situ conversion of oil shale to organic matter pyrolysis reaction process, and laid a theoretical foundation for the efficient, economical and stable operation of oil shale in-situ conversion projects.

The Devonian–Carboniferous (D–C) transition coincides with the Hangenberg Crisis, carbon isotope anomalies, and the enhanced preservation of organic matter associated with marine redox fluctuations. The proposed driving factors for the biotic extinction include variations in the eustatic sea level, paleoclimate fluctuation, climatic conditions, redox conditions, and the configuration of ocean basins. To investigate this phenomenon and obtain information on the paleo‐ocean environment of different depositional facies, we studied a shallow‐water carbonate section developed in the periplatform slope facies on the southern margin of South China, which includes a well‐preserved succession spanning the D–C boundary. The integrated chemostratigraphic trends reveal distinct excursions in the isotopic compositions of bulk nitrogen, carbonate carbon, organic carbon, and total sulfur. A distinct negative δ¹⁵N excursion (~−3.1‰) is recorded throughout the Middle Si. praesulcata Zone and the Upper Si. praesulcata Zone, when the Hangenberg mass extinction occurred. We attribute the nitrogen cycle anomaly to enhanced microbial nitrogen fixation, which was likely a consequence of intensified seawater anoxia associated with increased denitrification, as well as upwelling of anoxic ammonium‐bearing waters. Negative excursions in the δ¹³C_carb and δ¹³C_org values were identified in the Middle Si. praesulcata Zone and likely resulted from intense deep ocean upwelling that amplified nutrient fluxes and delivered ¹³C‐depleted anoxic water masses. Decreased δ³⁴S values during the Middle Si. praesulcata Zone suggests an increasing contribution of water‐column sulfate reduction under euxinic conditions. Contributions of organic matter produced by anaerobic metabolisms to the deposition of shallow carbonate in the Upper Si. praesulcata Zone is recorded by the nadir of δ¹³C_org values associated with maximal △¹³C. The integrated δ¹⁵N‐δ¹³C‐δ³⁴S data suggest that significant ocean‐redox variation was recorded in South China during the D–C transition; and that this prominent fluctuation was likely associated with intense upwelling of deep anoxic waters. The temporal synchrony between the development of euxinia/anoxia and the Hangenberg Event indicates that the redox oscillation was a key factor triggering manifestations of the biodiversity crisis.

In the oil shale in situ conversion project, it is urgent to solve the problem that the reaction degree of organic matter cannot be determined. The yield and composition of organic products in each stage of the oil shale pyrolysis reaction change regularly, so it is very important to master the process of the pyrolysis reaction and reservoir change for oil shale in situ conversion project. In the in situ conversion project, it is difficult to directly obtain cores through drilling for kerogen maturity testing, and the research on judging the reaction process of subsurface pyrolysis based on the maturity of oil products has not been carried out in-depth. The simulation experiments and geochemical analysis carried out in this study are based on the oil shale of the Nenjiang Formation in the Songliao Basin and the pyrolysis oil samples produced by the in situ conversion project. Additionally, this study aims to clarify the evolution characteristics of maturity parameters such as effective biomarker compounds during the evolution of oil shale pyrolysis hydrocarbon products and fit it with the kerogen maturity in the Nenjiang formation. The response relationship with the pyrolysis process of oil shale is established, and it lays a theoretical foundation for the efficient, economical and stable operation of oil shale in situ conversion projects.