Productivity Prediction Model for Horizontal Wells of Shale under Cyclic Conflagration Compression Fracturing Percussion.

A multiscale complex fracture and matrix damage coupled productivity prediction model under cyclic percussion of horizontal wells is established, according to the evolution of matrix permeability and the characteristics of complex fracture seepage after cyclic conflagration compression fracturing. The effects of the conflagration loading rate, cyclic percussion times, horizontal in situ stress difference, seepage interference, and wellbore pressure drop on horizontal well productivity are analyzed. The results show that the loading rate and percussion times are positively correlated with the production growth rate, but the growth through percussion has a threshold. Besides that, the length of the branch fracture is closer to that of the main fracture when there is a small stress difference, which results in a higher initial productivity and recovery degree of the gas well. Additionally, section spacing can affect the distribution of the pressure field and flow field around the well. An excessive spacing can lead to bending of flow field around the well, while a too small value is able to aggravate interjoint interference. Therefore, the critical section spacing, which can establish pressure communication between sections, is taken as the optimal section spacing. According to our work, when the fracture half-length is 5, 7, and 9 m, the optimum section spacing is 15, 25, and 30 m, respectively. Under this condition, when the horizontal length exceeds 800, 700, and 500 m, the influence of the wellbore pressure drop on the productivity of horizontal wells should be considered.