Numerical simulation of multistage fracturing optimization and application in coalbed methane horizontal wells

Multistage fracturing technology is critical to coalbed methane (CBM) production from horizontal wells. Further, optimizing the fracture parameters has a crucial influence on the stimulated reservoir volume and gas production. To investigate fracture parameter optimization, a stress interference model, hydraulic fracture propagation model, and a CBM productivity model are proposed. The effects of crack length and spacing for one to three fractures on the induced stress are calculated by implementing a static analysis MATLAB-developed program. The extended finite-element method is used to study the mechanism of simultaneous fracturing and sequential fracturing. In addition, the influences of cluster spacing and stage spacing on the stress field, formation pressure, fracture geometry, gas production, and reservoir pressure drop are comprehensively investigated by using Abaqus and COMET3 software. The simulation results indicate that with multiple fractures, fracture spacing of 80 m and fracture length of 160 m are conducive for dilating the secondary fracture system and producing a broader contact area in the coal seam. Moreover, an optimal cluster spacing of 15 m, a fracture interval of 80 m, and two cluster numbers per stage are better at forming a uniform fracture geometry with low injection pressure; within a given horizontal well section length of 500 m, fracture parameters with cluster spacing of 30 m, fracture spacing of 80 m, and two clusters per stage offer the best production performance. The simulation results are applied in well TP-07, and microseismic monitoring was conducted to monitor fracture propagation. The microseismic monitoring results are consistent with the numerical simulation.