• Comprehensive Quantitative Analysis of Fracture and Pore Evolution under Stress Release • This study integrates 2D slice imaging and 3D core reconstruction techniques to systematically investigate porosity, fracture connectivity, and morphological changes in deep coal seam reservoirs under various stress release conditions. Quantitative results demonstrate that stress release significantly enhances coal permeability, especially under high initial stress conditions (>30 MPa), highlighting its critical role in improving coal reservoir seepage channels. • Systematic Investigation of the Coupled Effects of Stress Release Rate and Gradient on Pore Evolution and Fracture Connectivity Through multiple crossover tests, the study systematically evaluates the effects of different stress release rates (0.5 MPa/min and 1 MPa/min) and gradients (10 MPa and 15 MPa) on fracture propagation, porosity enhancement, and connectivity optimization. The findings clarify the regulatory mechanisms of stress release parameters on coal permeability and propose optimized matching strategies for stress release rate and gradient. • Revealing the Key Role of Gradient Stress Release in Promoting Cooperative Fracture Network Expansion under High Initial Stress The study finds that under high initial stress conditions (35–45 MPa), gradient stress release significantly promotes cooperative expansion and connectivity enhancement of fracture networks, effectively improving methane migration capacity and providing new theoretical and technical support for deep coal seam reservoir development. • Development and Validation of a Pressure Relief Effect Evaluation Model for Deep Coal Seams Based on experimental data, a pressure relief effect evaluation model was developed and validated against field application results. This model bridges laboratory findings with practical engineering, offering technical support for optimizing stress release design and ensuring safe and efficient exploitation of deep coalbed methane. Despite its potential for deep coal seam stimulation, the large scale application of stress release technology remains limited by the lack of quantitative evaluation methods and physically interpretable models for parameter optimization. In this study, a controlled stress release experimental framework was established to investigate the effects of three key parameters, including the initial stress level, stress release magnitude, and stress release rate, on pore-fracture evolution in coal. High resolution micro CT scanning and three dimensional reconstruction were used to quantitatively characterize pore structure, throat geometry, and connectivity before and after stress release. The results show that stress release significantly increases reservoir porosity, connected pore volume, and coordination number, indicating enhanced pore connectivity and seepage capacity. A higher stress release rate of 1 MPa/min promotes microfracture activation and throat enlargement, whereas a larger stress release magnitude of 15 MPa further strengthens fracture connectivity and pore–throat coupling. Under higher initial stress conditions, stress release induces a more evident multi scale pore–throat response characterized by the simultaneous development of small pores, large pores, and intermediate to large throats. Based on these observations, a quantitative evaluation model for stress release effectiveness was established by relating stress release parameters to pore-fracture structural evolution. The model was validated using field data from the Daning–Jixian Block and shows good agreement with the observed production response. The proposed model provides a quantitative framework for evaluating stress release modification and optimizing stress release parameters in deep coalbed methane reservoirs.
Yao et al. (Fri,) studied this question.