Research on Seepage Characteristics of Y-Shaped Fractures Under Different Fracture Roughness

Abstract

Fractures are widely distributed in coal, and studying the seepage characteristics of fluids in Y-shaped fractures is of great significance for unconventional natural gas extraction and prevention of gas disasters. In this paper, based on the W-M fractal function, a Y-shaped fracture model with different roughness is established. The different seepage characteristics caused by rough morphology characteristics and roughness difference of the Y-shaped fracture is systematically studied, and the influence of fracture roughness on fracture seepage characteristics and fracture roughness difference on fracture fluid competitive diversion capacity are discussed. The results show that the fracture roughness is an important factor affecting the seepage characteristics of the fracture. When the fractal dimension of the fracture is identical, the outlet flow rate, velocity and Re all increase with the increase of the inlet pressure, and the flow regime is unchanged. The increase in the fracture roughness will lead to significant momentum loss and enhance the flow resistance of the fracture. In addition, the roughness difference between the branch fractures of the Y-shaped fracture is the key factor to control the fluid competitive diversion phenomenon. The larger the roughness difference between the two branch fractures, the greater difference in flow velocity, and the more significant change in flow rate proportion. As the inlet pressure increases, the two branch fractures Re gradually increases and Eu decreases, which smooth branch fracture Re grows faster, its Eu is much smaller than rough branch fracture Eu, and the smooth branch fracture competitive diversion capacity is enhanced. These results can provide new insights for the exploitation of underground fluid resources.