Experimental Investigation on Fracture Geometry in Multi-stage Fracturing under Tri-axial Stresses

Horizontal-well multi-stage fracturing was an effective stimulation technique, which was commonly used in unconventional reservoir. The complex interactions between multiple hydraulic fractures were believed to have a significant impact on fracture geometry inside the rock mass. Many theoretical models proposed to predict the hydraulic fracture geometry and stress interference in multi-stage fracturing had not been experimentally proved. In this study, a multi-stage fracturing test utilizing gal solution as fracturing fluid were conducted utilizing tri-axial fracturing system. Multi fractures were observed in a cubic rock sample. Experimental results showed that first stage fracture was a planar fracture while the second stage fracture was a concave fracture (bowl-shaped fracture). Stress interference between those two main fractures caused the growing of secondary cracks which were parallel to the simulated wellbore, but decreasing the width of sequent main fractures. Penny-shaped fracture model was believed to be more suitable than rectangular fracture model to simulate the real hydraulic fracture geometry in horizontal well. Fracture spacing design should be a significant work in multi-stage fracturing in horizontal well.