Evaluation of Present Tectonic Stress Field and Permeability of Coalbed Methane Reservoirs by Inversion of Logging Data From Longtan Formation, Dahebian Block

The permeability of coal reservoirs is predominantly controlled by the present tectonic stress field. This study systematically integrates macro‐ and micro‐scale analytical methods to investigate the controlling mechanisms of tectonic stress on pore‐fracture characteristics and permeability in the Longtan Formation coal reservoirs. Laboratory experiments were conducted to determine coal porosity, pore‐throat distribution, and microfracture development characteristics. Results indicate an mean porosity of approximately 3.5%, with a dominant pore diameter of ~8.38 nm. As burial depth increases, fractures and pores become progressively infilled with detrital materials, leading to a significant reduction in permeability. Dynamic mechanical parameters and present tectonic stress data were acquired using XMAC‐II logging, revealing maximum horizontal principal stresses ranging from 17.99 to 25.144 MPa and minimum horizontal principal stresses 11.63 to 15.88 MPa. Porosity and permeability exhibit synchronous covariation with horizontal stress variations, demonstrating that geostress governs the evolution of coal porosity, thereby dominating permeability. A quantitative model characterizing coal reservoir permeability‐horizontal stress relationships is established. Numerical simulations demonstrate that fault zones act as concentrated stress‐release areas, forming peripheral banded low‐stress zones where permeability peaks exhibit outward diffusion and gradual decline from fault cores. In contrast, synclinal structures exhibit reduced porosity and lower permeability due to compaction‐induced pore closure.