Effect of perforation friction on 3D In-stage multiple fracture propagation: A numerical study

Abstract

Due to the strong stress shadow and fluid competition, multiple fractures within one stage (in-stage) typically propagate un-evenly during hydraulic fracturing. Limited-entry fracturing, i.e. enhancing the perforation friction, has been applied to overcome the stress difference and promote the fluid uniform distribution among in-stage multiple fractures. This study established a three-dimensional in-stage multi-fracture propagation model based on the finite element method and the cohesive zone model. Moreover, a kind of fluid pipe element was created to capture the influences of perforation friction on fluid distribution and multi-fracture propagation. The input parameters of this model were set as the properties of the Jimsar shale oil reservoir, west of China. Some important factors including the number of fractures within one stage, fracture spacing, and perforation friction, have been investigated. As for the target reservoir, our simulation results show that the stress shadow between multiple fractures could be offset by appropriately increasing the perforation friction. To obtain uniform fracture propagation in Jimsar Oilfield, the effective perforation friction of three, six, or nine clusters in one-stage are all at least 7.5 MPa when the fracture spacing is 10 m; When the fracture spacing is 20 m, the effective perforation friction of single-stage with three, six, and nine fractures in one-stage are at least 2.5 MPa. Secondly, increasing the number of fracture clusters has a negative effect on the fracture propagation of multiple fractures whatever the fracture spacing is ten or twenty meters. Thirdly, when considering perforation erosion, the perforation friction designed on-site should be much higher than the effective perforation friction after perforation erosion. When the effective perforation friction is 2.5, 5.0, and 7.5 MPa, and the on-site design friction at least requires 15.20, 30.39, and 45.50 MPa, respectively. This study suggests that perforation friction, fracturing spacing, and the number of fractures should be optimized integrally, effectively improving stimulation effectiveness.