Experimental study on the propagation mechanism of hydraulic fracture in glutenite formations

Due to the existence of gravels in a glutenite formation, the geometry of hydraulic fracture becomes more complex, which makes the stimulation treatment difficult. In order to investigate the propagation mechanism of hydraulic fracture, laboratory experiments were performed on six natural glutenite samples, using a large scale tri-axial fracturing simulation system. The influences of the horizontal stress difference, gravel size and distribution, fracturing fluid viscosity and pumping rate on the fracture propagation were analyzed. The experimental results show that a single planar hydraulic fracture was created when the small gravels dominated in the glutenite sample. This indicates that small gravels have no obvious influence on the fracture propagation. By contrast, the hydraulic fracture was deflected along the interface of gravels and resulted in a complex fracture geometry with multiple tortuous branches in samples with large gravels. This phenomena is more distinctive when a sample with randomly distributed large gravels was hydraulically fractured under a lower horizontal stress difference. Additionally, a higher breakdown pressure was observed in the injection pressure curve when the hydraulic fracture initiated within a high-strength gravel. The fracture branching or deflecting is likely to reduce the fracture width. The fracture width was effectively increased when the high-viscosity fracturing fluid such as guar gel was used which is helpful for preventing sand plug. © 2017, Science Press. All right reserved.