Abstract: Fluid flow tests were conducted on artificial fracture networks with different numbers of intersections and subjected to various boundary load conditions. For all cases, the inlet hydraulic pressures were ranged from 0 to 0.6 MPa, and the lateral pressure ratios were increased from 1.0 to 5.0. The test results show that the Forchheimer’s law provides an excellent description of the nonlinear fluid flow in fracture networks. Both the linear and nonlinear coefficients in the Forchheimer’s law generally increase as the lateral pressure ratio increases but decrease as the number of intersections increases. During the fluid flow process, relationships between nonlinear effect factor E and hydraulic gradient J can be well described using a power function. The nonlinear effect factor E shows an increase with the hydraulic gradient. As the lateral pressure ratio increases, the critical hydraulic gradient shows an increasing trend. For all numbers of intersections (1-12), in the range of lateral pressure ratio from 1.0 to 5.0, the critical hydraulic gradient shows an increase from 0.63-12.13 to 6.01-81.55. A mathematical model of for decreased normalized transmissivity against the hydraulic gradient was established. An increase in the lateral pressure ratio shifts the fitted curves upward. The coefficient generally presents an increasing trend with the lateral pressure ratio. Equivalent permeability of the fracture networks decreases with the lateral pressure ratio.

Key words: lateral pressure ratio, fracture networks, number of intersections, nonlinear fluid flow, critical hydraulic gradient, normalized transmissivity