Study of nonlinear hydraulic characteristics and hydraulic aperture calculation of crossed fracture

Fluid flow tests are conducted on an artificial crossed fracture model. The relations between flux and pressure are obtained under different combinations of inlets and outlets. For these connected fractures, indeterminate equations are utilized to calculate the hydraulic aperture of each fracture element with the least squares method. The geometry of the fracture intersection is reproduced with topology method. The effect of fracture intersection on hydraulic characteristics is researched by solving Navier-Stokes equations. The results show that the fracture aperture for each fracture element can be accurately calculated based on flow test results and equations of hydraulic aperture. Within the fracture intersection, static flow and vortexes are observed respectively at lower Reynolds numbers and higher Reynolds numbers(R(e >=)100). It is shown that the inertial force is far larger than the viscous force and the cubic law is no longer applicative. For the cases with one inlet and two outlets, the normalized flow rate exhibits a quadratic relationship with the Reynolds number, especially when Reynolds number is large. The flow rate difference between the two outlets can be as much as 15%. The ratio of hydraulic aperture e to mechanical aperture E-0, i. e. e/E-0, varies with the increase of Reynolds number at the inlet. The value of e/E-0 shows linear, little nonlinear and strong nonlinear relations respectively when Re<1, 1<R-e<10, R-e>10. A nonlinear modified cubic law is obtained with the relation between e/E-0 and Re. This modified cubic law can be utilized to solve the nonlinear hydraulic characteristics caused by fracture intersections.