An Alternative BEM for Simulating the Flow Behavior of a Leaky Confined Fractured Aquifer With the Use of the Semianalytical Approach

This study developed an alternative boundary element method (BEM) to simulate the transient flow behavior of groundwater induced by well extraction in a confined‐fractured aquifer containing a network of discrete or connected fractures. The matrix flow, network‐fracture flow, and matrix‐fracture fluid exchange were considered. The aquifer was treated as a heterogeneous whole that consisted of fracture and matrix blocks with locally homogeneous hydraulic properties. The fractures were explicitly represented to be of true finite volume rather than nonrepresentational line sources. A semi‐analytical solution was developed based on the theory of a BEM in the Laplace‐transform domain, but the analytical Green's function was used for the bounded domain rather than the free‐space Green's function in a conventional BEM. Case studies were presented in order to investigate the flow‐exchange behavior between the matrix and fractures and the corresponding transient‐drawdown response. The results showed that: (1) Exchange‐flux distribution calculated with the classical infinitesimal fracture model was consistent with the difference of the normal drawdown derivative values on both sides of the fracture body in our model. (2) When the well was in the matrix, the fractures acted as both highly‐conductive conduits and leaky faults, and the drawdown‐derivative behaviors resembled the characteristics of a Warren & Root (1963) dual‐porosity reservoir model. (3) When the well was in the network fracture and when the volume of fracture was of the same order of magnitude as the matrix, the drawdown derivative might exhibit the look‐alike behavior of a dual‐porosity model.