A new particle tracking algorithm has been developed for the general case of irregular grids. Particle velocity magnitudes and directions are determined from interpolations of phase fluid fluxes across cell faces. The interpolation is based on particle coordinates in unit cube space and the edge directions of the cell. Cell transformation functions are used in transforming coordinates between physical space and unit cube space. Transformation parameters and cell edge directions are calculated once at the beginning of the simulation. Special treatments are given to cells with wells or fault connections to take into account their impacts on the particle velocity. A more accurate high-order tracking method is applied where the timestep is subdivided if a particle enters a neighboring cell or reflects during a timestep. The interpolation process then continues for the remainder of the timestep using the new cell data. A dispersion mechanism is included in the model which can be defined as either isotropic or non-isotropic.

The new algorithm has been implemented into our commercial three-dimensional, three-phase reservoir simulator, VIP. This enables the simulation of tracer flow within the framework of three-dimensional, multiphase, unsteady state reservoir simulation. The tracers are non-partitioning, and can be injected at various concentrations with either the gas or water phases. Since the algorithm is applicable for irregular grids, it becomes possible to be applied for field applications that have to use corner point grids to deal with complicated reservoir structure and geometry. The algorithm has been tested and validated on one- and two-dimensional models with analytical solutions and applied to field scale tracer applications. Three-dimensional visualization and animation of the particle paths and fronts has demonstrated the effectiveness of the tracking algorithm.

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