Optimization of Fracture Propagation in Coal Seams Using Discrete Lattice Method: Case Study of the L Block, China

Abstract

Hydraulic fracturing, an effective method for enhancing coal seam productivity, largely determines coalbed methane (CBM) production, which is significantly influenced by geological and engineering factors. This study focuses on the L block to investigate the mechanisms influencing efficient fracture propagation and enhanced stimulated reservoir volume (SRV) in fracturing. To explore the mechanisms influencing effective fracture propagation and enhanced SRV, the L block was selected as the research object, with a comprehensive consideration of geological background, reservoir properties, and dynamic production data. By combining the discrete lattice method with numerical analysis and true triaxial experimental simulation, the fracture morphology of a single cluster and the propagation patterns of multiple clusters of complex fractures were obtained. Additionally, the optimization of temporary plugging timing and the fracture map under multiple factors were innovatively proposed. Results indicate that greater flow rate and viscosity can effectively overcome the stress shadow effect of the outermost fractures (1st and 6th clusters), increasing the fracture pressure of the single cluster and the equilibrium degree of multiple fracture propagation, thus forming a more complex fracture network. Moreover, when viscosity exceeds 45 mPa·s, pressure concentrates at fracture tips, promoting discontinuous propagation and reducing flow resistance. Conversely, increased gangue thickness and spacing between horizontal wells increase the vertical propagation pressure, suppressing fracture growth and reducing central flow velocity. This study provides a multi-cluster fracture propagation map for optimizing volumetric fracturing in coal seams and suggests that the optimal temporary plugging time significantly enhances the SRV.