Wenbin Jiang

Fluid invasion into low-permeability formations requires overcoming threshold pressures governed by capillary entry and yield stress mechanisms. Current engineering practice relies on time-consuming core-flood experiments or oversimplified capillary bundle models that neglect three-dimensional pore connectivity, limiting their applicability to subsurface energy systems such as CO2 geological storage, dense nonaqueous phase liquid (NAPL) migration, and hydrocarbon accumulation. This study develops a computationally efficient framework based on a statistically representative ensemble of 6260 stochastic pore networks spanning broad geological variability. Invasion percolation algorithms determine threshold pressure (gradient) under single-phase, two-phase, and coupled mechanisms. Statistical analysis reveals robust power-law scaling between threshold pressure and the characteristic throat radius Rc50 derived from mercury injection capillary pressure curves, enabling rapid prediction without three-dimensional imaging. Furthermore, spatial wettability allocation modes, NAPL-wet preferentially assigned to large, small, or random throats, alter percolation pathways; networks with ≥70% NAPL-wet throats require no threshold pressure regardless of the spatial pattern. Linear superposition of capillary and yield stress contributions introduces acceptable engineering error (<20%) compared to fully coupled calculations. By resolving three-dimensional connectivity and local wettability states, this framework provides an image-free computational tool for evaluating critical invasion pressures in subsurface two-phase displacement processes.

The Deyang–Anyue rift trough is a key target for Lower Cambrian Qiongzhusi shale gas exploration in the Sichuan Basin, yet inorganic pore heterogeneity across structural positions remains poorly constrained. Shales from the fifth sublayer in intratrough and trough-margin settings were analyzed using an integrated large-scale Mosaic scanning electron microscopy (LAM-SEM)─advanced mineral identification and characterization system (AMICS) workflow, enabling pixel-scale mineral–pore registration and quantitative characterization of inorganic pore types, area fraction, size distribution, and morphology. Intratrough shales, mainly organic-rich to organic-moderate quartz-rich felsic shales, exhibit low inorganic pore area fractions but larger average pore sizes with predominantly unimodal distributions. Their pores are elongated and irregular, showing high eccentricity and low circularity, and are mainly feldspar-hosted dissolution pores. In contrast, trough-margin shales display higher inorganic pore area fractions, smaller pore sizes, and particularly locally multimodal size distributions in organic-lean feldspar-rich shales. These pores are more equant and smoother, characterized by lower eccentricity and higher circularity. Mineral composition and TOC jointly control inorganic pore structures: quartz content is positively correlated with pore size, whereas feldspar content shows a negative correlation. Easily soluble minerals are positively correlated with pore circularity, whereas clay minerals show a negative correlation. In addition, TOC promotes heterogeneous dissolution, leading to decreased circularity and increased eccentricity. These findings reveal two contrasting inorganic pore development patterns within the rift trough and provide new insights into pore evolution mechanisms and reservoir quality variations in deeply buried marine shales, offering a basis for deep marine shale reservoir evaluation and exploration target optimization.

Hydraulic fracture network initiation and propagation in tight sandstone are strongly controlled by mineral heterogeneity and fluid–solid interaction. However, existing numerical models still have limited capability in simultaneously representing multi-mineral distributions and dynamically coupled fracture-fluid processes. In this study, a two-dimensional polygonal discrete element fluid–solid coupled model was established based on mineralogical images of tight sandstone. Compared with conventional continuum-based approaches, the proposed model is better suited to describing fracture initiation, branching, and network evolution in multi-mineral granular media. Under dimensionless operating conditions calibrated against field data, coupled and uncoupled formulations were systematically compared to evaluate the role of hydro-mechanical interaction during hydraulic fracturing. The coupled simulations generated consistently more fractures than the uncoupled simulations over the investigated injection-rate range, with an average increase of 28.7% and a maximum increase of 67.2%. Compared with the uncoupled model, the coupled model also predicted higher breakdown pressures and stronger fracture-tip pressure concentrations, and the breakdown pressure increased with injection rate. Under low injection rates, the coupled formulation reproduced pressure-buildup-driven fracture-tip advance, whereas the uncoupled formulation failed to sustain fracture propagation. Under higher injection rates, the coupled formulation produced multilayered and highly branched fracture networks, while the uncoupled formulation mainly generated simple first-order branching. These results demonstrate that hydro-mechanical coupling is a controlling mechanism for fluid-energy dissipation, fracture-tip pressure evolution, and complex fracture network formation in tight sandstone. This study provides an image-based polygonal DEM framework for evaluating hydro-mechanical fracture network evolution in multi-mineral tight sandstone.

Understanding pore-scale oil-water two-phase flow dynamics in reservoir rocks is fundamental for optimizing petroleum exploitation. However, limitations in real-time observation have hindered comprehensive characterization of these processes. This study employs a novel three-dimensional visualization platform that integrates online micro-CT imaging (3.78 μm resolution) with oil-water displacement experiments in Berea sandstone. Experiments conducted at 20 °C and 50 °C across flow rates (0.10–0.35 mL/min) revealed distinct temperature-dependent saturation patterns: non-monotonic N-type behavior (initial increase, decrease, and then increase with flow rate) at 20 °C and V-type behavior (initial decrease followed by increase) at 50 °C, accounting for 76.0–94.3% of observed variations. Quantitative analysis demonstrated that these dominant patterns correlate with the evolution of maximum oil cluster volumes and their dynamic merging-splitting processes. Significantly, we identified temperature-sensitive preferential flow pathways that maintain stable oil phases independent of flow rate variations, occupying 17.1% and 13.6% of pore space at 20 °C and 50 °C, respectively. These findings advance our understanding of oil migration mechanisms by revealing temperature-dependent non-monotonic saturation patterns and quantifying the dynamics of preferential pathway formation, providing insights for optimizing reservoir development through enhanced characterization of fluid distribution patterns at varying depths and temperature conditions.

Basalt is a suitable target area for CO₂ storage. Clarifying the evolution of the pore structure during CO₂–fluid–basalt interactions is a crucial element in the preparation of a CO₂ geologic storage operation. In this study, a pore-scale phase field model is proposed to simulate the CO₂–fluid–basalt interaction process of Snake River Plain basalt. Our model is suitable for complex multimineral natural rocks, and the initial mineral distribution before the reaction can be completely based on a real 3D rock image without the need to simplify the mineral geometry. The simulation results demonstrate that after 120 days of dissolution–precipitation reaction, the volume of secondary minerals (3.75%) exceeds that of dissolved minerals (2.01%), leading to a reduction in porosity by 1.74%. The pore structure of the basalt changes significantly, and the connectivity is obviously reduced. The effects of temperature and pressure on the reaction rate were examined to guide site selection for CO₂ sequestration. The results show that increasing temperature and pressure can accelerate the reaction rate, but the impact of pressure on the reaction rate is negligible compared to the significant influence of temperature. Therefore, an area with a high geothermal gradient is conducive to geological sequestration.

Food security is a goal and means of global sustainable development, and an important component of China’s national security. Based on grain production data from 2000 to 2020, 31 provinces (cities, autonomous regions) in China were used as research units to analyze the spatiotemporal differences and driving forces of grain production in China using a combination of local correlation index, center of gravity transfer model, and geographic detector. The results as follows, ① During the research period, China’s total grain production showed a decrease followed by an increase, and the yield per unit area of grain showed an increasing trend. Corn has become the "largest staple food" in China; ② During the research period, the focus of China’s grain production continued to shift northward, with Heilongjiang, Henan and Shandong provinces becoming the main grain production areas, with Henan being the province where China’s grain production center was located. Among the factors affecting grain yield, the effective irrigation area (0.971) has the strongest explanatory power. Finally, countermeasures and suggestions were proposed from five aspects, stabilizing grain production, reducing grain inventory pressure, implementing regional grain security responsibilities, improving grain circulation efficiency, promoting high-quality grain engineering construction, adjusting grain production structure, strictly implementing farmland protection responsibilities, scientifically applying pesticides, fertilizers and other production materials, emphasizing agricultural infrastructure construction and stabilizing the number of agricultural labor force.

Investigating immiscible displacement in fractured porous media is essential for understanding the two-phase flow behavior within pores and fractures. In this work, a three-dimensional pore-fracture network model was developed to address the influence of fracture on flow patterns and to characterize fracture-matrix crossflow under different flow conditions. Sensitivity studies at a wide range of viscosity ratios and capillary numbers underscored that fracture significantly influenced flow patterns in the capillary fingering zone. Fracture with an advantageous path effect in the displacement direction caused a shift in the boundary of capillary fingering zone toward an increase in capillary numbers. As fracture aperture decreased and aspect ratio increased, there was a discernible decline in the crossflow rate. When fracture aperture equaled average matrix throat diameter, fracture lose advantageous path effect in compact displacement zone but retained it in viscous fingering and capillary fingering zones. Distinct matrix-fracture crossflow development processes were observed in different zones: in cross zone, following displacement breakthrough, the crossflow underwent a “long-term” process to attain stability. Viscous fingering zone promptly achieved stability post-breakthrough, whereas both capillary fingering and compact displacement zones had already reached a stable state before breakthrough. Nonlinear variations in breakthrough saturation were observed in the cross zone between compact displacement and capillary fingering zones. The control process of immiscible displacement exhibited variability under different flow conditions: compact displacement zone was characterized by matrix dominance, viscous fingering zone was jointly controlled by matrix displacement and fracture-matrix crossflow, and capillary fingering zone was primarily governed by fracture-matrix crossflow. These findings enhance scholarly comprehension of immiscible displacement behavior in fractured porous media.

Low-temperature nitrogen adsorption is a widely used method for the research and evaluation of gas shale’s pore structure. The existing interpretation method, utilizing gas adsorption isotherms to obtain pore size distribution (PSD), is always based on the one-dimensional geometry model, while the void space of gas shale has strong multi-dimensional characteristics. It is necessary to investigate the nitrogen condensation and evaporation behavior in multidimensional structures. In this study, a series of two-dimensional and three-dimensional models based on ink-bottle pores were constructed. A hybrid molecular simulation approach combining grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) is proposed to simulate the low-temperature nitrogen adsorption isotherms. Three aspects have been analyzed in detail. Compared with the conventional understanding that the threshold of cavitation in the ink-bottle pore only relates to throat diameter, this study discloses a wider and more comprehensive range of conditions of cavitation that considers both the throat length and diameter. As pore spaces of shale samples consist of many complex interconnected pores, the multi-stage ink-bottle pore model is more suitable than the single ink-bottle pore model to similarly reproduce the wider cavitation pressure range. A more universal parameter is proposed that quantitatively unifies the influence of cavity diameter and length on condensation pressure and has good applicability in cavities with different shapes. This work quantitatively studies the nitrogen adsorption isotherms of three-dimensional complex nanopore structures using molecular simulation and provides a reasonable explanation for the low-temperature nitrogen adsorption isotherms of gas shale.