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

摘要

Multi-stage fracturing operations in horizontal wells would create multi-stage hydraulic fractures, the complex interactions between which would have a significant impact on fracture geometry inside the rock mass. In this paper, a model of the wellbore under three-stage fracturing operations is designed and a cement block with the size of 400mm*400mm*400mm is selected to conduct the fracturing experiment under tri-axial stresses. It is observed from the experimental results that the first-stage fractures are planar fractures and the second-stage fractures are deviated single-slot fractures, while the third-stage fractures are concave fractures (bowl-shaped fractures). The secondary fractures are also found to grow in the area of stress interference between the firststage and second-stage fractures. It is also verified from the experiment that the stress interference between the fractures of different stages is the key factor that affects the fracture geometry during multi-stage fracturing. The induced stress on the planes of former stage fractures would cause the diversion of latter stage fractures. Therefore, during the multi-stage fracturing operations of horizontal wells in field, the stress interference can be adequately utilized to optimize the fracture operation so as to create complex fractures and connect natural fractures in the reservoir, which would improve the fracturing results.