PREDICTIVE UNDERSTANDING OF BIOGEOCHEMICAL REACTIONS IN HETEROGENEOUS POROUS MEDIA

Water-rock-microbe interactions play a pivotal role in applications relevant to energy, water, and environment. It is important to understand, quantify, and predict biogeochemical processes in shallow critical zones as well as in deep oil and gas reservoirs. The extent and rates of these interactions are dictated by an array of factors including reactive mineral abundance, water flow, and spatial patterns that regulate water distribution. In this talk I will share some thoughts learned from our recent work on the role of spatial heterogeneities in determining biogeochemical reactions integrating column experiments (tens of centimeters), field studies (tens of meters), and reactive transport modeling. At the column scale, flow-through experiments and modeling have shed lights on how spatial patterns of magnesite dictate its dissolution rates under a variety of flow velocity and permeability contrast conditions. At the field scale, the spatial distribution of water-conducting properties and mineral reactivity synergize to govern where, when, and how much microbe-mediated bioreduction (sulfate-reducing and iron-reducing) reactions occur in engineered uranium bioremediation experiments at Rifle, CO. At both scales, a relatively small proportion of the reactive minerals effectively participate in reactions; reaction rates are highest when the characteristics of spatial heterogeneities maximize the water conducted through the biogeochemically-active zones. Insights gained here have interesting implications for applications relative to water, energy, and environment.