Evolutions of Anisotropic Hydraulic Properties of Rough-Walled Rock Fractures under Different Shear Displacements

Abstract

Four cylindrical sandstone samples were extracted from the original rectangular sample with a rough-walled fracture. Each drilling angle (θ) of cylindrical sandstone samples is different to consider the anisotropies of rough-walled rock fractures. For each sample, different flow velocities ranging from 0 m/s to 13 m/s were designed. For a given flow velocity, a series of different confining pressures ( σ n ), including 1.5 MPa, 2.5 MPa, and 3.5 MPa, were applied on the fractured samples. The hydraulic properties of each cylindrical sandstone sample were tested under different shear displacements ( u s ) and σ n . The results show that the hydraulic gradient ( J ) shows an increasing trend with the increment of σ n . With the increment of the Reynolds number ( Re ), the transmissivity ( T ) decreases in the form of the quadratic function. The normalized transmissivity ( T / T 0 ) decreases with the increment of J . The variations in T / T 0 with J can be divided into three stages. The first stage is that T / T 0 approximately holds a constant value of 1.0 when J is small indicating that the fluid flow is in the linear regime. The last two stages are that T / T 0 decreases with the continuous increase of J , and the reduction rate first increases and then decreases. The critical Reynolds’ number ( Re c ) of the sample angle with a drilling angle of 90° is different from that of other samples. The corresponding Re c is 6.52, 28.73, and 32.1 when the shear displacement u s = 2 mm , 3 mm, and 4 mm, respectively. The variations in Re c and J along different drilling angles are significantly obvious. When the confining pressure is large, the effect of anisotropy on Rec is much greater than that of confining pressure.