Improved Discrete Fracture Network Simulations for Flow in Fracture Rock

Abstract:

Groundwater flow in fracture rock is mainly controlled by networks of interconnected conductive fractures. The existing fracture network models have been developed to describe groundwater flow behavior in fracture rock, typically assuming that flow in all fractures has uniform characteristics, i.e., flow is either laminar or turbulent. However, turbulent and laminar flow may occur at the same time in the fracture rock with wide range of fracture sizes. In this study, we develop an improved approach to calculate flow rate and pressure distribution in the fracture network where both laminar and turbulent flows may exist. Reynolds number is used to distinguish flow characteristics in individual fracture. In fractures where flow is laminar, we use the cubic law for the transmissivity in conjunction with Darcy’s law to calculate the pressure distribution and flow behaviors. If the flow is turbulent, non-linear equations are used to describe the flow behaviors. Pressure and flow behaviors are examined in relation to fracture aperture sizes, boundary conditions, and fracture surface friction coefficients. Differences between the pressure distributions and flow rates in the fracture network from this study and those from previous approaches are explored and discussed. In particular, we examine the potential errors from the uniform flow characteristics assumption and investigate how the errors are related to fracture sizes and orientation distributions.