The fact that salt ions in shale pores diffuse into fracturing fluids is key factor to lead to recovered water with high salinity. In this paper, the authors conduct the test of mineral composition and SEM to understand the reservoir characteristics. The diffusion experiments are conducted on crushed samples, and a new method is proposed to differentiate between matrix and microfractures by using diffusion data. A large amount of salt ions exit in shale pores and can diffuse into fracturing fluids after fracturing operations. To a great extent, ion diffusion rate is determined by the development of microfractures. The crushed samples with smaller grain diameter contain have lower diffusion rate due to the low probability of microfractures development. When the grain diameter is lower than critical value, the crushed samples cannot contain microfractures. As for Longmaxi formation sample, the fracture-matrix boundary is about 80mesh.The research contributes to understanding the reservoir characteristics and salinity profiles of gas shale.

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