Prediction of interwell tracer flow behaviour in heterogeneous reservoirs

A new numerical approach has been developed for predicting the interwell tracer flow behaviour in heterogeneous porous media typical of water and oil reservoirs. This approach uses a mixed finite-element method with triangular elements to predict pressure and velocity fields, and a novel random walk model to simulate the tracer transport through the reservoir, and to perdict the concentration response at the production well. The mixed finite-element method solves the pressure and velocity simultaneously imposing suitable boundary conditions for both pressure and velocity, which allows the solution of the tracer velocity to be more accurate and to conserve mass more precisely than a standard finite-element method. The random walk model can reflect the tracer flow behaviour directly by tracking the movement of particles representing the tracer input volume.The technique has been validated by comparing the predicted results with analytical solutions of tracer concentration response for a homogeneous five-spot pattern, and with published experimentally observed tracer fronts at breakthrough for homogeneous and three heterogeneous cases of five-spot pattern. Good agreement has been achieved for all cases. The model presented in this paper is general, and can therefore be applied to drive patterns other than the five-spot pattern, and for different types of heterogeneities; it can also include effects such as longitudinal and transverse dispersion and adsorption.