This paper presents an analysis of the lower order spatial moments of colloidal transport in a coupled fracture-matrix system. For this purpose, colloidal transport is numerically modeled to obtain the spatial distribution of concentration profiles along the fracture. Implicit finite-difference numerical technique has been adopted to obtain the colloidal concentration in the fracture. Subsequently, the first and second spatial moments are evaluated using the colloidal concentration. The results suggest that effective velocity of the colloid is retarded by increment in rock matrix porosity, matrix diffusion coefficient, filtration coefficient, reduction of half-fracture aperture, initial colloid velocity, and remobilization coefficient. Significant mixing of colloids occurs in the fracture due to low-fracture aperture, initial colloid velocity, and filtration coefficient. © 2013 © 2013 Indian Society for Hydraulics.

Govindarajan Suresh Kumar

Department of Ocean Engineering

N. Natarajan

Colloids

Diffusion

Filtration

Numerical models

COLLOID TRANSPORT

COLLOIDAL CONCENTRATIONS

Concentration profiles

COUPLED FRACTURE-MATRIX SYSTEM

FILTRATION COEFFICIENT

FIRST AND SECOND SPATIAL MOMENTS

Remobilization

SPATIAL MOMENT

Fracture

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IIT Madras

Lower order spatial moments for colloidal transport in a fracture-matrix coupled system

ISH Journal of Hydraulic Engineering

In this study, the behavior of thermal fronts along the fracture is studied in the presence of fracture-skin in a coupled fracture-matrix system. Cold water is injected into the fracture, which advances gradually towards production well, while extracting heat from the surrounding reservoir matrix. The heat conduction into the fracture-skin and the rock-matrix from the high permeability fracture is assumed to be one dimensional perpendicular to the axis of fluid flow along the fracture. Constant temperature cold water is injected through an injection well at the fracture inlet. The fluid flow takes place along the horizontal fracture which ensures connectivity between the injection and production wells. Since the rock-matrix is assumed to be tight, the permeability of fracture-skin as well as the rock-matrix is neglected. The present study focuses on the heat flux transfer at the fracture-skin interface as against the earlier studies on fracture-matrix interface, and the sensitivity of additional heterogeneity in the form of fracture skin in a conventional fracture-matrix coupled system is studied. The behavior of thermal fronts for various thermal conductivity values of the fracture-skin and rock-matrix is analyzed. Spatial moment analysis is performed on the thermal distribution profiles resulting from numerical studies in order to investigate the impact on mobility and dispersion behavior of the fluid in the presence of fracture-skin. The presence of fracture skin affects the heat transfer significantly in the coupled fracture-matrix system. The lower order spatial moments indicate that the effective thermal velocity increases with increase in skin thermal conductivity and a significant thermal dispersion is observed at the inlet of the fracture owing to the high thermal conductivity of the fracture-skin at the early stages. Furthermore the higher spatial moments indicate that the asymmetricity increases with decrease in skin thermal conductivity unlike the case with half fracture aperture and fluid velocity and the kurtosis is maximum with higher skin thermal conductivity which implies enhanced heat extraction from the fracture-skin into the fracture. Results suggest that the amount of heat extraction by the circulating fluid within the fracture from the reservoir not only depends on the rock-matrix module of the reservoir characteristics but also the fracture-skin characteristics of the system and subsequently influence the reservoir efficiency. © 2011 Springer Science+Business Media B.V.

Geotechnical and Geological Engineering

Numerical Modeling and Spatial Moment Analysis of Thermal Fronts in a Coupled Fracture-Skin-Matrix System

A numerical model is developed for studying the transport of colloids accompanied by radionuclides in a coupled fracture-skin-matrix system. The radionuclides and the colloids are assumed to decay, sorb onto the fracture surface, as well as diffuse into the fracture-skin and rock-matrix. The sorption of the radionuclides onto the mobile and immobile colloids within the fracture is assumed to be linear. The governing equations describing the radionuclides and colloid transport along the fracture and diffusion into fracture-skin as well as rock-matrix, normal to the fracture axis are coupled with each other. The coupled non-linear equations are solved numerically with fully implicit finite difference method. Constant concentration is assumed at the inlet of the fracture for both colloids and radionuclide. A varying grid is adopted at the fracture and skin interface to capture the flux transfer. Sensitivity analysis is performed to investigate the effect of various colloid properties on the colloid concentration in the fracture-matrix coupled system in the presence of fracture skin. Results suggests that as the colloid velocity increases the diffusion of colloids into the fracture-skin decreases due to the low residence time available for the colloids, resulting in higher colloidal concentration in the fracture. It is observed that as the filtration coefficient increases, the colloidal concentration in the fracture decreases as more colloids are filtered from the aqueous phase. The reverse mechanism occurs in the case of remobilization coefficient. Further, the effect of colloidal dispersion coefficient and diffusion into the fracture-skin on colloid migration was analysed. The concentration profiles for various diffusion coefficients of colloids in the fracture-skin pose an unusual behavior. © 2010 Elsevier B.V.

Colloids and Surfaces A: Physicochemical and Engineering Aspects

Radionuclide and colloid co-transport in a coupled fracture-skin-matrix system

A triple continuum one-dimensional transport model for colloid facilitated contaminant migration in sets of parallel fractures with fracture skin

Environmental Science & Technology

Removal of Biocolloids Suspended in Reclaimed Wastewater by Injection into a Fractured Aquifer Model

Water Resources Research

Fate and transport of pathogens in a fractured aquifer in the Salento area, Italy

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Open Access	No