Analytical model for tracer transport in reservoirs having a conductive geological fault

Geological faults are frequently found in oil reservoirs and their presence dramatically impacts the underground fluid motion. Tracer tests provide a mean to dynamically characterize the conduit or barrier behavior of the fault. Although diverse analytical models have been developed to describe tracer transport in a geological conductive fault, only few of them capture the fact that injection and production wells are regularly located outside the fracture plane. In many cases, the tracer path length outside the fault structure is significant. In this work the system is represented by three coupled regions associated to the injector-to-fault, fault, and fault-to-production-well zones. The coupling is simplified by considering linear flow and aligned regions. This model includes hydrodynamic dispersion, an important phenomenon not considered in previous work. One-dimensional advective–dispersive tracer transport is assumed in each region. Border conditions require tracer mass conservation. The initial condition is a Dirac delta pulse at the injection site. The equations are analytically solved in Laplace space and the inverse transform is evaluated numerically by the Stehfest algorithm. Four specific cases have been studied; they comprehend a long and a short fault path length having low or high dispersivity respectively. The pulse behavior and the tracer breakthrough curve, as well as their sensitivity to fault dispersion, fault length and fault fluid velocity are analyzed. Clear differences in the pulse profile and breakthrough curve shape are found in relation to the case when no fault is present.