Targeted delivery of nanoparticles to a heterogeneous crude oil zone in an unsaturated porous medium

Abstract

Targeted delivery of engineered nanoparticles (NPs) in situ has the potential to efficiently distribute NPs throughout a target treatment zone while decreasing the required mass of NPs to achieve treatment goals. Amphiphilic co-polymers have been proposed as practical NP coatings to promote attachment to target non-aqueous phase liquids (NAPLs) under saturated and unsaturated conditions. Currently, investigations have been limited to in one-dimensional systems; to capture some field-scale complexity, this study evaluated NP transport and binding to a heterogeneous crude oil source zone in a less constrained unsaturated system using a two dimensional (2-D) physical model. NP transport and retention in this system was characterized using a single porosity transport model with depth-dependent straining and kinetic attachment/detachment reactions. Although preferential and stronger attachment of NPs to the crude oil source zone was demonstrated, significant NP retention was also observed between the infiltration gallery and the top of the crude oil zone due to straining and possible aggregation. In addition, the presence of preferential flow paths reduced delivery efficiency to segments of the crude oil zone with either a higher crude oil saturation or thickness. Simulation results provided satisfactory fits with the experimental observations. This study revealed the significant role that physical heterogeneity (e.g., permeability and water content) plays in NP transport and binding, and that it must be considered when designing NP delivery strategies for targeting source zones in minimally constrained, unsaturated systems.