Upscaling simulation method of fluid flow for fracturing-shut in-flowback-production process in tight oil reservoirs: Hysteresis effects of capillary pressure and relative permeability

Abstract

The hysteresis effect is a key factor to accurately predict the fluid distribution and production performance of fracturing-shut in-flowback-production (FSFP) process in tight oil reservoirs. In this paper, the upscaling simulation method of fluid flow for FSFP process has been proposed. This method, which establishes the connections between the pore network model (PNM) and the reservoir numerical model, not only effectively characterizes the hysteresis effects of capillary pressure and relative permeability in tight oil reservoirs, but also realizes the upscaling process from the pore-throat scale to the reservoir scale. First, the quasi-static pore network model for tight oil reservoirs considering the boundary layer has been established. And then, the capillary pressure curves and relative permeability curves of the drainage process (non-wetting phase displacing wetting phase process) and imbibition process (wetting phase displacing non-wetting phase process) have been obtained. Moreover, the hysteresis model has been added to numerical simulation of FSFP process and the hysteresis scanning curves have been calculated. Finally, a numerical model considering different hysteresis effects for multistage-fractured horizontal well of a tight oil reservoir located at Ordos Basin, China, has been established to investigate the oil saturation change and oil recovery during the whole process of FSFP. The results show that the hysteresis effects of capillary pressure and relative permeability will increase the predicted exchange volume of oil-water between matrixes and fractures in fracturing-shut in process, and decrease the predicted oil recovery in flowback-production process. Which is proved by the actual production performance of the tight oil reservoir developed by elastic energy.