Stress interference and propagation uniformity in multi cluster hydraulic fracturing using a coupled XFEM based CZM model

The uniform propagation of multiple hydraulic fractures is crucial to maximize the volume of stimulated reservoirs and improve the recovery of hydrocarbons in unconventional reservoirs. However, simultaneous fluid injections often result in non-uniform fracture growth due to strong stress interference between adjacent clusters. The unresolved issue is a quantitative ranking of how the spacing of the clusters, the count of the clusters, the injection rate and the viscosity of the fluid control the uniformity of propagation under matched geomechanical conditions. This study addresses that gap using a two-dimensional plane strain coupled XFEM based CZM model for simultaneous multi-cluster fracture propagation from a horizontal wellbore in a tight and low-permeability reservoir. The model is verified against the analytical solution dominated by toughness of KGD and applied to fourteen parametric cases covering cluster spacing of 20 to 35 m, injection rate of 0.001 to 0.005 m3/s per cluster, fluid viscosity of 10 −3 to 10 −1  Pa s, and two to five clusters. Results show that coalescence of individual stress shadows into a continuous compressive stress umbrella is the main cause of non-uniform growth, with interior clusters confined while exterior fractures propagate more freely. Fracture spacing is the dominant control and increasing spacing from 20 to 30 m raises the uniformity index from 0.42 to 0.94 and supports uniform growth to 88 to 95 m. Cluster count is the second strongest control, injection rate has a secondary non-monotonic effect, and fluid viscosity has negligible influence on uniformity. The sensitivity ranking is first the fracture spacing, followed by the group count, the injection rate, and the viscosity of the fluid. For the modeled formation, 30 m spacing favors uniform simultaneous propagation, whereas spacing below 25 m may require sequential or zipper initiation.