Microbially induced calcium precipitation is a promising method for sealing fractures in low-permeability reservoirs, yet the role of anaerobic indigenous microorganisms under reservoir conditions remains unclear. In this study, reservoir samples were anaerobically enriched, and a urease-producing indigenous strain identified as Bacillus megaterium was isolated. Its growth, environmental tolerance, stimulation response, biomineralization products, and fracture-sealing performance were systematically evaluated. The strain showed good adaptability to fractured reservoir conditions and produced extracellular polymeric substances that promoted calcium enrichment and calcite formation. Visual fracture experiments demonstrated that microbial cementation significantly reduced fracture permeability and achieved effective sealing. The results further indicate that the dominant sealing mechanism depends on fracture aperture: surface adsorption controls sealing in narrow fractures, whereas particle deposition, settling, and migration become increasingly important in wider fractures. These findings clarify the fracture-sealing mechanisms of indigenous anaerobic microorganisms and support their potential application in subsurface permeability control.

High-entropy single-atom (HE SAs), distinguished by maximized atomic utilization efficiency and tunable coordination geometries, represent a frontier in atomic-scale electromagnetic wave (EMW) absorber design. Nevertheless, precise HE SAs synthesis and atomic-level structure–absorption correlation mapping remain formidable challenges. Herein, we report an entropy-stabilization strategy to co-anchor multiple transition metals within a carbon matrix, concurrently suppressing atomic aggregation while engineering asymmetric charge distributions and enhanced electronic conductivity for superior EMW dissipation. Differential electronegativity and ionic radii among multimetallic sites induce localized asymmetric coordination environments, generating intensive electric dipole polarization centers. Synergistic multielement interactions further drive rapid interfacial charge redistribution and efficient electron transfer, significantly boosting conduction loss. The optimized HE SAs@CN system achieves exceptional EMW absorption: a minimal reflection loss of −76.8 dB at 8.57 GHz and a 5.00 GHz effective absorption bandwidth at 2.81 mm thickness, outperforming all benchmark single-metal analogs. This study establishes HE SA-doped carbon architectures as a paradigm for dielectric property modulation, providing fundamental insights into atomic-scale EMW loss mechanisms.

There are few studies on the stress sensitivity of reservoirs at the micropore structure level. A porous carbonate core of the fourth member of the Sinian Dengying formation gas reservoir in Central Sichuan is selected to conduct an in-situ submicron CT permeability stress sensitivity test. The experimental results show that the permeability of porous carbonate rock decreases obviously with the increase of effective stress. Increasing effective stress decreases the pore volume, pore throat diameter, and throat length. The probability distribution of the shape factor curve shifts to the right, while the diameter of the pore throat distribution curve and the throat probability distribution curve of the core shift to the left. In different pressure stages, it has different effects on different sizes and shapes of pores. For micro pores and throats, the damage is obvious, and the connectivity of the pore throat becomes poor. The change in pressure causes a change in the core micropore structure, which leads to the decline of core permeability. With the decrease of effective stress, the core permeability cannot be restored, which indicates that the damage caused by stress sensitivity is irreversible.

Supercritical CO₂ (SC-CO₂) fracturing stands out a promising waterless stimulation technique in the development of unconventional resources. While numerous studies have delved into the induced-fracture mechanism of SC-CO₂, the small scale of rock samples and synthetic materials used in many studies have limited a comprehensive understanding of fracture propagation in unconventional formations. In this study, cubic tight sandstone samples with dimensions of 300 mm were employed to conduct SC-CO₂ fracturing experiments under true-triaxial stress conditions. The spatial morphology and quantitative attributes of fracture induced by water and SC-CO₂ fracturing were compared, while the impact of in-situ stress on fracture propagation was also investigated. The results indicate that the SC-CO₂ fracturing takes approximately ten times longer than water fracturing. Furthermore, under identical stress condition, the breakdown pressure (BP) for SC-CO₂ fracturing is nearly 25% lower than that for water fracturing. A quantitative analysis of fracture morphology reveals that water fracturing typically produces relatively simple fracture pattern, with the primary fracture distribution predominantly controlled by bedding planes. In contrast, SC-CO₂ fracturing results in a more complex fracture morphology. As the differential of horizontal principal stress increases, the BP for SC-CO₂ fractured rock exhibits a downward trend, and the induced fracture morphology becomes more simplified. Moreover, the presence of abnormal in-situ stress leads to a further increase in the BP for SC-CO₂ fracturing, simultaneously enhancing the development of a more conductive fracture network. These findings provide critical insights into the efficiency and behavior of SC-CO₂ fracturing in comparison to traditional water-based fracturing, offering valuable implication for its potential applications in unconventional reservoirs.

Proppant transport within fractures is one of the most critical tasks in oil, gas and geothermal reservoir stimulation, as it largely determines the ultimate performance of the operating well. Proppant transport in rough fracture networks is still a relatively new area of research and the associated transport mechanisms are still unclear. In this study, representative parameters of rough fracture surfaces formed by supercritical CO₂ fracturing were used to generate a rough fracture network model based on a spectral synthesis method. Computational fluid dynamics (CFD) coupled with the discrete element method (DEM) was used to study proppant transport in this rough fracture network. To reveal the turning transport mechanism of proppants into branching fractures at the intersections of rough fracture networks, a comparison was made with the behavior within smooth fracture networks, and the effect of key pumping parameters on the proppant placement in a secondary fracture was analyzed. The results show that the transport behavior of proppant in rough fracture networks is very different from that of the one in the smooth fracture networks. The turning transport mechanisms of proppant into secondary fractures in rough fracture networks are gravity-driven sliding, high velocity fluid suspension, and fracture structure induction. Under the same injection conditions, supercritical CO₂ with high flow Reynolds number still has a weaker ability to transport proppant into secondary fractures than water. Thickening of the supercritical CO₂ needs to be increased beyond a certain value to have a significant effect on proppant carrying, and under the temperature and pressure conditions of this paper, it needs to be increased more than 20 times (about 0.94 mPa s). Increasing the injection velocity and decreasing the proppant concentration facilitates the entry of proppant into the branching fractures, which in turn results in a larger stimulated reservoir volume. The results help to understand the proppant transport and placement process in rough fracture networks formed by reservoir stimulation, and provide a theoretical reference for the optimization of proppant pumping parameters in hydraulic fracturing.