Laboratory study of chemical transport to wells within heterogeneous porous media

Abstract

A laboratory flow cell was used to study chemical transport to wells producing water from two realizations of a heterogeneous porous medium. The wells produced water from a confined aquifer which was otherwise governed by a mean uniform hydraulic gradient. For both realizations the aquifer was composed of a two‐dimensional, lognormally distributed, second‐order stationary, exponentially correlated conductivity field. For the first realization, response was monitored at a single well 45 integral scales from the inflow boundary. Four wells were used in the second realization, with locations ranging from 10 to 45 integral scales from this boundary. The focus of this work was on the nature of the dispersion observed in the chemical arrival at the pumping well, and this work builds on an earlier study in which it was shown that results under mean uniform flow were relatively consistent with stochastic theories for fluid flow and chemical transport under mean uniform flow. Consistent results were obtained across the two realizations for the wells located 45 integral scales from the boundary as the breakthrough curves demonstrated an increase in dispersive behavior with an increase in the ratio of the pumping rate to the regional flow, consistent with existing theory for finite‐sized sources. In contrast, results for the well located closest to the source (10 integral scales) demonstrated variability in the timing and shape of the breakthrough curves that did not correlate with the ratio of pumping at the well to regional flow. The results indicate that the shape and timing of a breakthrough curve at a well producing within a regional flow field may be strongly dependent on the distance of the well from the source. Further, the parameters (e.g., dispersivity) obtained from analysis of the breakthrough curve are shown to be functions of the ratio of pumping rate at the well to the regional flux.