Abstract:

In light of the geological characteristics of continental shale oil reservoirs，a numerical model for unbalanced fracture propagation during horizontal well intensive fracturing was constructed using the cohesive zone method to study the effects of cluster spacing and lamina on unbalanced propagation of multiple fractures and then elucidate the mechanism of unbalanced fracture propagation during horizontal well intensive fracturing. True triaxial physical simulation experiment was conducted on samples taken from the field outcrop of shale oil reservoirs to investigate the mechanical behaviors of multi-fracture initiation and cross-interface propagation and thereby reveal the mechanism of mechanical interaction between fractures and lamina during intensive fracturing. Comprehensive analysis indicates that the development degree of lamina in shale oil reservoirs is the key determinant of the complexity of fracture network. Increasing cluster spacing effectively enhances the connectivity of the lamina and interfaces. The difference in propagation rate among fracture clusters decreases with the increase of cluster spacing，and the central fractures are more prominently affected by stress interference when cluster spacing is small. The multiple-clustered fractures exhibit a mutually complementary propagation pattern. Reasonably controlling cluster spacing can improve the vertical extension of fractures，thereby expanding the coverage of fracture system and enhancing the fracturing efficiency in shale oil reservoirs.

Key words: shale oil, reservoir, lamina, cohesive zone, horizontal well, intensive fracturing, induced fracture, unbalanced propagation, numerical model