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ABSTRACT: Migration and packing patterns of proppants play a critical role in the conductivity of hydraulic fractures and unconventional oil and gas production. However, the fracture surface is usually tortuous with gradually narrow walls (tortuous - wedge fractures). Existing fracture models only consider tortuosity, and more efforts are needed in this regard. In this study, a numerical model of proppant transport in tortuous wedge-shaped fractures is established based on CFD-DEM method, used to investigate the effects of tortuosity, wedge angle, diameter of proppant, fluid velocity on the migration and placement of proppants. The results reveal that the migration and distribution of proppant in tortuous-wedge fractures exhibit significant disparities when compared with straight fractures or tortuous fractures. Proppant migration in tortuous-wedge fractures is divided into the suspended sand stage, sand bed rapid growth stage and top suspended sand stage according to the main force. The proppant transport distance increases with the increase of the wedge angle. Compared with the tortuous fractures with a wedge angle of 0°, the migration distance of proppant in the tortuous wedge fractures, t = 1 s, wedge angles of 1° and 2° increased by 16% and 29%. However, with the increase of it, the congestion of the proppant may also occur, and there is a critical angle. The greater the tortuosity, the greater the kinetic energy loss of particles and the advancing angle of the dune. Compared with the straight fracture, t=3 s, and the average velocity is reduced by 36%, and 45%. In addition, the proppant migration in tortuous-wedge fractures is non-uniform distribution, and the dune is higher in the tortuous place. This study benefits to understand the migration mechanism of proppant in fractures. It can provide theoretical guidance for the stimulation of unconventional reservoirs. 1. INTRODUCTION Hydraulic fracturing is an important means of reservoir stimulation and improving oil and gas recovery. By pumping high - pressure fluid, the reservoir is broken and proppant particles are injected to fill the fractures, forming a long - term high conductivity channel for oil and gas in the reservoir. Proppant migration in fractures is a fluid - solid coupling problem among reservoir fluid, proppant particles and fracture walls. The migration and distribution of proppant depend on the physical parameters of particles, fluids and fractures, the distribution of flow field and pressure field in complex fractures, and the mechanism of action is complex. Scholars have carried out a lot of research based on indoor physical experiments and numerical simulation methods.
Yan et al. (Sun,) studied this question.