Investigation of the Contamination of Fractured Formations by Non-Newtonian Oil Pollutants

Abstract

In many practical applications, non-aqueous phase liquid (NAPL) pollutants exhibiting a clearly non-Newtonian rheological behavior (e.g. crude oil, suspensions of engine oils, asphalt, creosote, etc.) may migrate through fractured formations and contaminate aquifers. The present work is the first step toward the development of non-Darcian models concerning the non-linear NAPL flow in single fractures, and determination of the coupled effects of non-Newtonian NAPL rheology and flow rate on the transient immiscible displacement of an aqueous phase by a NAPL. Initially, a protocol is developed for the preparation and rheological characterization of synthetic non-Newtonian NAPLs, which are based on waxy oils. Then, an artificial transparent glass-etched single fracture of controlled morphology is fabricated and used for the measurement of the non-linear pressure gradient—superficial velocity relationship for the flow of NAPL of varying rheology. Pore network simulations and effective medium approximation (EMA) are used for the interpretation of the experimental results and derivation of an analytic non-Darcian one-phase flow model. Visualization experiments of the immiscible displacement of an aqueous phase by Newtonian and non-Newtonian NAPLs are performed on the artificial fracture under controlled values of the viscosity ratio and capillary number (ratio of viscous to capillary forces). Comparative study of the Newtonian and non-Newtonian NAPL flow patterns allows us to evaluate the interactive effects of NAPL rheology, flow rates and fracture morphology on the spatial and temporal distribution of such liquid pollutants within single fractures.