A three-dimensional numerical investigation of the propagation path of a two-cluster fracture system in horizontal wells

Multiple-stage and multiple-cluster fracturing technology is commonly used in horizontal wells to enhance the permeability in unconventional reservoirs. Understanding the propagation path of a multiple cluster fracture system in three dimensions is of great importance for spacing design in practice. In this study, a fully hydromechanical coupled numerical model was used to investigate the propagation path of a two-cluster perforation fracture system. Several influencing factors, including three-dimensional (3D) stress anisotropy, well deviation, stress heterogeneity and Young's modulus heterogeneity created using layered strata or a random distribution, were studied. A basic understanding of the spatial path of a two-cluster fracture system was obtained. According to the study, it was found that 1) three dimensional propagation path of a cluster fracture system is not symmetrical but quite complex due to the local disturbance of stresses and material properties; 2) three-dimensional (3D) stress anisotropy and heterogeneity are the most important factors that control the reorientation and the propagation of a cluster-fracture system; 3) layered stress reverse has a significant influence on irregular fracture reorientation and propagation; 4) fracture height of cluster fractures will increase, and fracture aperture will decrease when the stress-shadow effect is strong; 5) layered Young's modulus distribution had a limited influence on fracture reorientation, but a strong influence on fracture propagation; 6) on engineering scale, cluster fractures cannot have an ideal form symmetric to the well due to the combined effects from the stress shadow between fractures, heterogeneity of the stress and material properties, well deviation, formation inclination, and other factors.