The accurate access to fracture conductivity plays a critical role in shale fracturing optimization. Shale is characterized by complex mineral composition, well-developed bedding, and rougher fracture surface after fracturing, which presents a huge challenge to the repeatability and accuracy of fracture conductivity experiment. In this study, an experimental program is proposed to measure the fracture conductivity of shale using the highly replicas of rough original fractures. As indicated by the results, due to the impact of fracture surface roughness, the propped aligned fracture conductivity does not simply increase as a function of increasing concentration. At a certain closure stress, there may be an optimal proppant concentration to improve conductivity. Proppants could significantly enhance the capability of maintaining fracture conductivity under relatively high closure stress. Although the shear displacement of fracture surfaces could improve conductivity, shear fractures still require proppants to ensure high and stable conductivity under high closure stress. As the proppant concentration increases, the roughness impact is reduced, and the fracture conductivity is dominated by proppant properties.

1. Introduction

At present, hydraulic fracturing provides an essential solution to shale reservoir stimulation (Bandara et al., 2020; Lu et al., 2020). Large-scale low viscosity slick water and relatively low concentration proppant are pumped into shale formations to construct complex fracture networks, thus achieving the effective development of shale reservoirs (Zou et al., 2015). Due to the impact of in-situ stress, rock strength, and natural fractures, there are a large number of complex fractures caused, including main fracture and branch fracture. The main fractures have high proppant concentration, while the branch fracture can be propped open with low concentrations of proppant and shear rough surface (Enriquez-Tenorio et al., 2018; Fredd et al., 2000). The conductivity of the fracture network is a determining factor in the productivity of shale. Therefore, it is of much practical significance to evaluate and predict the conductivity of various fractures in shale reservoirs accurately.

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