This paper presents a new numerical approach which models interwell tracer flow paths in transient two-phase flow in heterogeneous porous media. The approach adopted is sequential in that the velocity and pressure fields are solved simultaneously using a mixed finite element approach, the phase saturation is solved by mass balance, and then the tracer is transported and its concentration at the production well is predicted using a random walk model. Mass conservation has been achieved throughout all the numerical procedures.
Comparative studies between conventional finite difference methods and the methods presented in this paper show a significant reduction of numerical dispersion by the new method. Effects of physical dispersion, adsorption, two-phase flow and transient state on tracer flow behaviour are presented. Tracer test cases for a quarter five-spot pattern with homogeneous permeability and with assumed heterogeneities are analysed. A multi-well, irregularly shaped reservoir case has also been presented.