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Abstract

Geological storage of anthropogenic CO₂ emissions in deep saline aquifers has recently received tremendous attention in the scientific literature. Injected CO₂ plume buoyantly accumulates at the top part of the deep aquifer under a sealing cap rock, and some concern that the high-pressure CO₂ could breach the seal rock. However, CO₂ will diffuse into the brine underneath and generate a slightly denser fluid that may induce instability and convective mixing. Onset times of instability and convective mixing performance depend on the physical properties of the rock and fluids, such as permeability and density contrast. The novel idea is to adding nanoparticles to the injected CO₂ to increase density contrast between the CO₂-rich brine and the underlying resident brine and, consequently, decrease onset time of instability and increase convective mixing.

As far as it goes, only few works address the issues related to mathematical and numerical modeling aspects of the nanoparticles transport phenomena in CO₂ storages. In the current work, we will present mathematical models to describe the nanoparticles transport carried by injected CO₂ in porous media. Buoyancy and capillary forces as well as Brownian diffusion are important to be considered in the model. IMplicit Pressure Explicit Saturation-Concentration (IMPESC) scheme is used and a numerical simulator is developed to simulate the nanoparticles transport in CO₂ storages.

Introduction

In the recent years, the applications of nanometer particles (nanoparticles) have been reported in many disciplines. These nanoparticles can modify the rheology, mobility, wettability, and other properties of the fluids and therefore need comprehensive investigations. Using the nanoparticles in oil and gas exploration and production is also a promising field of research. For example, certain types of nanoparticles can be used as tracers for oil and gas exploration. These nanoparticles are designed such that they do not stick to the rock surface or hydrocarbon phases and move faster than the traditional chemical tracers. Moreover, nanoparticles can be used in the oilfields to enhance water injection by virtue of changing the wettability of reservoir rock through their adsorption on porous walls.