Particle tracking simulation for tracer dispersion in porous media: A five-spot laboratory model

The tracer test is a useful method to investigate various phenomena in geological porous media such as groundwater contaminant transport, sweep efficiency and retention time in oil reservoir, fractures orientation assessment, and geothermal reservoir characterization. The use of numerical analysis is important to assist any interpretation of tracer test results. In many cases, the schemes of commonly employed numerical methods are limited by computational restrictions, such as finer grid requirements and small calculation steps to avoid excessive numerical error. In this study, an analog model of a quarter five-spot porous reservoir was simulated by using random walk Particle Tracking (PT) method. Instead of solving Darcy's equation to obtain grid velocities, this numerical scheme utilizes method of images with pairs of sink-source potential flow to generate velocity vectors. Unlike the conventional grid method, this method provides inherently smooth and continuous flow field at arbitrary position within the reservoir model. We compare the breakthrough concentration profiles and the flow visualizations by using PT with experimental results and the Eulerian-grid based finite volume method by solving the advection-diffusion equation. The results show that the predicted breakthrough curves of tracer concentration and visualizations have good agreement to the experimental model.