Influences of perforation parameters on the fracture initiation in thin coal bed groups

The stimulation effect of thin-coalbed gas reservoir is particularly influenced by perforation parameters due to its higher stress sensitivity and interbeded characteristics. In this paper, the seepage-stress-damage coupling model was used to optimize the perforation parameters of thin coal bed group, and combined with field logging and construction data, the initiation and propagation of hydraulic fractures in thin coal beds was simulated under different perforation parameters. Then, based on the reservoir damage volume, the influences of perforation parameters on the stimulation effect were quantitatively evaluated. Finally, the factors influencing coal bed productivity and the stimulation mechanisms of indirect fracturing were analyzed, and the indirect fracturing of the roof and floor of thin coal bed was numerically simulated. The simulation results show that the number of perforations has the greatest influence on the damage volume, perforation depth and phase angle take the second place, and perforation spacing has the least influence. Compared with the conventional fracturing, the indirect fracturing of roof and floor perforation needs longer pumping time and higher pumping pressure. The finite element numerical model established in this study can be used to analyze the fracture initiation near the wellbore and is of instructive significance to the optimization design of field perforation and fracturing.