Investigation of a critical choke during hydraulic-fracture flowback for a tight sandstone gas reservoir

Low porosity and permeability in a tight sandstone gas reservoir can cause problems during fracturing. If the fracturing fluid cannot be discharged in a timely fashion after fracturing, the fracturing fluid will move into the deep formation and result in secondary damage. Conversely, if the flowback rate of the fracturing fluid is too high, it will cause the proppant to backflow and reduce the efficiency of fracturing operation. Therefore, it is very important to control the choke sizes and flowback rates for the flowback process of a tight sandstone reservoir. In this study, a model of the time of the closed fracture considering the principle of material balance is built. Subsequently, the relationship between the wellhead pressure and the optimum diameter of the choke at different times is obtained using hydrodynamics and particle dynamics theory. Finally, the proposed optimization method is applied to an actual well from the Xinjiang tight gas reservoirs. Results show that a choke diameter can be reasonably optimized under different wellhead pressures, and that fracturing fluid flows back as much as possible and without proppant backflow. A sound design of a fracturing fluid flowback system is also provided. This study presents the mechanism of post-fracturing management and provides a better understanding of the flowback system in tight gas reservoirs.