Distribution Characteristics and Interaction Mechanisms of In Situ Stress Field, Microstructures, and Fractures in the Zhengzhuang Block

To clarify the distribution patterns and interaction mechanisms of the in situ stress field, microstructures, and fractures and to provide geological support for efficient coal-bed methane (CBM) development in the Zhengzhuang Block, this study investigates the No. 3 and No. 15 coal seams. Using Anderson’s in situ stress classification theory, we quantitatively characterize in situ stress distribution, microfracture development, and microstructural features through injection-falloff tests, hydraulic-fracturing microseismic monitoring, logging interpretation, and core analysis to systematically explore their coupling mechanism. Vertically, in situ stress increases linearly with burial depth: reverse-strike-slip stress regimes occur above 700 m, strike-slip regimes occur at 700–900 m, and normal-faulting regimes occur below 900 m. Planarly, the No. 3 coal seam exhibits high-north–low-south stress, whereas the No. 15 seam shows high-west–low-east stress; the maximum horizontal principal stress generally trends NE-NEE. Fracture development is structurally controlled with correlations among the relevant parameters, and the No. 3 seam shows superior fracture development concentrated within tectonically active zones. Five microstructural units are identified using three-dimensional modeling with distinct petrophysical properties; steep-slope zones display the greatest parameter discreteness. Coupling obeys the principal stress-dominant, structure-carrier, and coal-rock-response principles. Eleven coupling modes are proposed for the No. 3 seam and seven for the No. 15 seam. The steep-slope–high-Poisson-ratio–strike-slip-stress mode is most conducive to coordinated fracture growth. This work reveals the structure–stress-fracture coupling mechanism for high-rank coal reservoirs and provides a reference for fracturing-scheme optimization and coalbed-methane exploitation in analogous Qinshui-Basin settings.