Characteristics of Spatial Distribution of Geostress in Deep Coal Seams and Its Control On Hydraulic Fracture Formation

Abstract “Background:” This study aims to reveal the spatial distribution of in-situ stress direction and magnitude in deep coal seams and its impact on the propagation of hydraulic fracturing-induced fractures. “Method of approach:” Numerical simulation and microseismic monitoring were used to model and validate the formation and expansion of fractures under complex coal structure and in-situ stress. “Results:” (1) The orientation of the maximum principal stress in the Benxi Formation is predominantly EW, with some wells exhibiting directions of NNE-SWW and SEE-NNW. (2) Low stress differences increase fracture width and the pressure needed to initiate cracking is reduced. high differences have the opposite effect. (3) For coal with its original structural integrity, the semi-length of fractures first increases and then diminishes as stress differences rise, whereas in granulated coal, this semi-length keeps on increasing. Fracture height shows a non-linear pattern with stress differences. (4) When horizontal stress is highest, fractures are horizontal. When vertical stress is highest, fractures are typically vertical. If vertical stress is between horizontal stresses, fractures tend to be vertical. When vertical stress is close to horizontal stress, complex fracture networks are likely. “Conclusions:” Low stress differences promote wider fractures and lower the pressure threshold for cracking, while high stress differences have the inverse effect.The integrity of the coal seam plays a critical role in the growth pattern of fractures. The orientation of fractures is closely tied to the prevailing stress conditions.