Research On The Mechanism Of Leak-off And Flowback Of Fracturing Fluid In Low Permeability Reservoir

Hydraulic fracturing is one of the most effective stimulation methods for low permeable reservoir. Most of the low permeability reservoirs have small pore and fine throat, high filtration resistance. During the fracturing fluid flowback process, much amount of the fracturing fluid is detained in the layer, which caused the extremely low fluid flowback and seriously affecting the fracturing effects. Therefore, it is of great significance to looking for measures to improve the flowback rate and removal the water lock in order to guarantee the fracturing effect.For this point, dynamic and static filtration experiments were done to analyze the mechanism of leak-off and its influence factor. The mechanism of leak-off and flowback of fracturing fluid in oil-wet or water-wet reservoirs could be observed and analyzed from micro-seepage experiments. Core displacement experiments were conducted to study the low flowback rate of fracturing fluid and its influence factors. The local grid refinement technology was used to build the conceptual model to simulate fractured horizontal wells, in order to research the leak-off range and determine the standard of the end of the fluid flowback process, then to calculate and analyze the flowback rate of fracturing fluid and its affecting factors.Cores experiment results show that the permeability of formation have a significant impact on the flowback rate of fracturing fluid. The lower the permeability is, the smaller the flowback rate of fracturing fluid is. In the same testing conditions, the flowback rate of fracturing fluid declines with the increase of the oil viscosity and the interfacial tension between oil-fracture fluid filtrate. With the flowback pressure increases, the flowback rate of fracturing fluid becomes higher. It has important implications for improving the flowback rate of fracturing fluid to decrease of the oil viscosity and the interfacial tensions between oil-fracture fluid filtrate. Numerical simulations show that the fluid leak-off range increases with the increasing of the fluid injection in the same leak-off time. The more the fracture numbers of the horizontal well are, the higher flowback rate of fracturing fluid is. Moreover, the flowback rate of fracturing fluid becomes higher as the increase of the flowback pressure difference and flowback velocity.