Competitive Propagation Laws of Hydraulic Fractures in Multiple Thin Coal Seams

This study investigates nonuniform hydraulic fracture propagation in vertically stacked thin coal seams with small interlayer spacing. A discrete element-based numerical model incorporating dynamic interlayer flow allocation was developed to simulate competitive fracture behavior. Key findings include: (1) As interlayer stress difference increases (from 1.5 to 4 MPa), fractures shift from interlayer penetration to coal seam propagation, with main seam fracture length growth dropping sharply (from 18.37-20.73% to 2.59-6.07%) and nonuniform propagation coefficient rising (from 0.06 to 0.33). When the leakoff coefficient increases (from 0.0005 to 0.0030 m/min^0.5), the thinnest seam's fracture length reduces by 36.70% while its flow proportion increases (from 12 to 33%). (2) Flow allocation trends: higher stress difference favors thick seams; elevated leakoff benefits thin seams; increased thickness proportion advantages thick seams (11#flow: from 38 to 60%). (3) Due to significant physical property differences between coal seams and roof/floor rocks (coal elastic modulus: 5-12 GPa vs roof/floor elastic modulus: 25 GPa), fractures primarily extend along coal seams with strong roof/floor barrier effects (coal flow >90%). (4) Increased coal seam thickness proportion enhances the competitive advantage of thick seams, with the nonuniform propagation coefficient remaining at 0.28 and thin seam propagation being suppressed. This work provides a theoretical basis for optimizing multithin-layer coal seam fracturing. This work provides a theoretical basis for optimizing multithin-layer coal seam fracturing.