Ceramic proppants are critical products for holding induced fractures open and enhancing hydrogen productivity in low‐permeability reservoirs. Though the effects of proppant size and proppant type on the well productivity have been well studied in the past, the role of the proppant surface wettability in the oil flow performance has not been thoroughly investigated. To help the readers and the industries understand the wetting behavior of ceramic proppants, this research was designed to analyze the effect of the proppant wettability on the flow efficiencies of oil and water under different conditions (for example, various proppant size, water saturation, and waterflooding). Also, it was required to determine the optimal wettability of proppants in the available candidates for the enhancement of oil recovery in the hydraulic fracturing process. Results of the work indicate that the proppant wettability plays an essential role in the productivities of water and oil in tight sandstones. Compared with the same‐size oil‐wet proppants, the mixed‐wet proppants contribute to increasing the oil flow efficiency and reducing the produced volume of water. However, an increased value of proppant size can significantly enhance the oil recovery. Besides, using the oil‐wet proppants, the waterflooding phenomenon can lead to a lower oil recovery than that of the non‐water‐flooded specimen. Based on the findings of the microscopic structural characteristics of the proppant surface, a fluid channel mechanism was proposed to help understand the proppant wettability effect on the flow behaviors of oil and water. This research can provide guidance on the determination of proppants in the designs of hydraulic fracturing operations. These findings can help the reservoir engineers dealing with hydraulic fracturing better design the surface wettability of the proppants, especially for those reservoirs with a multi‐phase flow.

Since the invention of the Brazilian test about eight decades ago, discussions on the validity of indirect tensile strength measurement by the Brazilian test have always been of focus in rock fracture mechanics. According to the principles of the Brazilian test, experimental data are only valid when a fracture is initiated at/near the disc-shaped planar center and propagates along the diametral loading plane. However, traditional experimental results can only show readers a final failure instead of fracture process. Meanwhile, the accuracy of analytical solutions and numerical simulations are profoundly dependent on the input of underlying assumptions. To overcome the confusion about the Brazilian test, this study proposed to combine the Brazilian test with digital image correlation. By visualizing a dynamic fracture process of fracture initiation and propagation, the validity of the Brazilian test can be verified. This study can well explain the underestimation of rock tensile strengths in traditional Brazilian tests. Additionally, the specimen should have a length to thickness ratio larger than 0.30 to minimize the compression effect near the loading contacts. Due to the intrinsic heterogeneity of the rock structure, a small deviation of fracture initiation does not make a big difference in the experimental results.