An Analysis of Advection-Dispersion Ratio to Incorporate Dispersive Transport into Streamline Simulation

摘要

Streamline simulations have been extensively used due to its computational speed and freedom from numerical dispersion. However, many works have been applied to transport modeling without considering dispersive transport. A new term, an advection-dispersion ratio is introduced, which is defined as a relative extent of advection to dispersion along a streamline. Using the advection-dispersion ratio, analytical solution to the advection-dispersion equation is mapped onto streamlines so that dispersive transport can be effectively modeled by streamline simulation. With the advectiondispersion ratio incorporated, streamline simulation was applied to transport in an artificially fractured sample, and the simulation result was compared to experimental result. It is observed that the tracer breakthrough curve from the simulation matches well with that from the experiment. In addition, the tracer displacement profile matched that of experiment well. By allocating various advection-dispersion ratios to streamlines, streamline simulations were performed on various fields generated by sequential Gaussian simulation to analyze the effect of the advection-dispersion ratio on transport modeling. Then, the results were compared with simulation result using a single representative advection-dispersion ratio over the flow domain. The simulation results indicate that a representative advection-dispersion ratio is applicable when the advection-dispersion ratio is large. On the other hand, advection-dispersion ratio should be allocated differently to each streamline with respect to the characteristics of the streamline, when the representative advection-dispersion ratio is small. Moreover, similar permeability is apt to be clustered spatially in a field of high correlation length, which yields diverse and contrastable streamline characteristics in the standpoint of advection-dispersion ratio. Therefore, the results using the single representative advection-dispersion ratio differ from those using various advection-dispersion ratios along individual streamlines.