Quantitative experimental study on the rule of fluid flow and its influencing factors in hydraulic fractures

Hydraulic fracturing has become a necessary tool for developing unconventional oil and gas resources. The goal is to create fractures in the subsurface and transport proppant from the surface into the subsurface fractures, which is accomplished by pumping a high-pressure fluid to open formation and using the energy of fluid to extend the fractures. Then, the fluid carries the proppant into the fracture and fills it. Therefore, the fluid plays a crucial role in the fracturing process, and the rule of fluid flow in the fracture affects the effectiveness of hy-draulic fracturing. Based on this, this paper establishes a quantitative experimental device to simulate the process of fluid being injected into a fracture. The device achieves the first acquisition of the information of the flow field in the fracture by introducing the technology of particle image velocimetry (PIV). Our study found that the fluid flows through the perforation tunnel will occur obvious jet phenomenon thus causing the formation of a large number of vortices in the flow field near the entrance of fracture, and the turbulence of the flow field is high and the fluid flow is complex. As the fluid flows toward the distal end of the primary fracture, the vortices in the flow field disappear, and the flow field gradually becomes stable and the fluid flow is regular. And according to the characteristics of the distribution of the vorticity of the fluid in the primary fracture, we divide the flow field into three main characteristic areas, namely, the jet vortex zone, the turbulent transition zone and the stable development zone. When the fluid flows to the secondary fracture, vortices are formed and there is a obvious area of disturbance which affects the flow of fluid. In addition, we analyzed the effects of pump rate, viscosity, and perforation location on each area in the fracture and obtained the main control factors for each zone. This study provides the first systematic analysis of the law of flow in the fracture from the perspective of flow field, which profoundly reveals the rule of fluid flow in the process of hydraulic fracturing. This study provides theoretical guidance for the design and optimization of fracturing schemes, and provides reference significance for the microscopic study of flow in the fracture.

Automated summary

This study establishes a quantitative experimental device to simulate the injection of fluid into a fracture. By using particle image velocimetry (PIV) technology, the device acquires the flow field information in the fracture for the first time. The study finds that the fluid forms vortices in the perforation tunnel, but as it flows towards the end of the fracture, the vortices disappear and the flow field becomes stable. The flow field is divided into different characteristic areas based on the distribution of vorticity. This study provides theoretical guidance for the design and optimization of fracturing schemes and has significance for microscopic studies of flow in fractures.