IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

A numerical model is developed and used to investigate the non-isothermal reactive fluid flow in a fracture. It considers the effect of thermal stresses and silica dissolution in a coupled fracture-matrix system using the dual porosity concept. The fluid flow is based on the Cubic law, and the transport mechanism in the fracture includes solute advection and dispersion. Solute mass exchange between the fracture and the rock matrix is accounted for using a lateral diffusion limited solute transport. The heat transfer between the fracture and the rock is modeled using a lateral conduction limited thermal flux from the reservoir into the fracture while heat transport within the fracture considers thermal advection, conduction, and dispersion. The pressure of the circulating fluid is allowed to vary keeping the discharge along the fracture a constant. As a result, the water velocity, the pressure change and the fracture aperture varies throughout the fracture. The numerical model is applied to examine the individual as well as the combined effect of thermal stress and mass of silica dissolved on the variation of fracture aperture between the injection and production wells with time. The resulting change in pressure distribution along the fracture is evaluated assuming a constant injection rate. Result suggest that there is a significant increase in fracture permeability and the associated pressure drop at the injection well may be mainly attributable to thermoelastic effects, while the increase in fracture aperture near the production well is mainly caused by silica dissolution.

Department of Ocean Engineering

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Transactions - Geothermal Resources Council

Evolution of fracture permeability and pressure with rock cooling and silica dissolution in a coupled fracture-matrix system: A numerical investigation

This paper presents an analysis using spatial moments for transport of nonreactive solutes in a single fracture-matrix system using a dual porosity framework. The velocity and dispersion obtained using the first and second spatial moments are found to have two regimes. The effect of fracture velocity, fracture dispersivity, fracture spacing, matrix diffusion coefficient, and matrix porosity on both regimes are analyzed. The first regime is characterized by a behavior wherein both velocity and dispersion are functions of time and all of the above parameters of the fracture-matrix system are found to have an influence. In the second regime, they are independent of time similar to the behavior of conservative solutes in an ideal porous media. This regime is characterized by the influence of a few parameters of the fracture-matrix system. The empirical relationships for solute velocity, macrodispersion coefficient, and dispersivity in the asymptotic stage are presented. Journal of Hydrologic Engineering © ASCE.

Journal of Hydrologic Engineering

Spatial moment analysis for transport of nonreactive solutes in fracture-matrix system

A numerical model is developed to simulate the coupled effect of thermal and reactive solute transport in a fracture. The analysis is based on the fluid circulation model in a single fracture with an injection well and a production well. The model includes thermal convection and dispersion along the fracture and transient heat exchange between the fracture and the reservoir matrix. The simulation of solute transport is incorporated by considering advection and dispersion of solutes along the fracture and one-dimensional diffusive limited solute transport in the reservoir matrix. The model is extended to simulate linear reaction kinetics of silica transport leading to a coupling between thermal and reactive solute transport processes. The model is used to examine the effect of rock-water interactions on the amount of silica mass transfer and fracture aperture variation. The maximum value of variation in fracture aperture occurs near the inlet. The peak is mitigated and is shifted away from the injection well with time.

Numerical modeling of coupled thermo-reactive solute transport in a fracture-matrix system

The stabilization of hydrodynamic flows was studied by small viscosity variations. The primary and secondary instability of simple channel flows was addressed. It was reiterated that the large effect was not due to a modified dissipation but due to reduced energy intake from the mean flow to the fluctuations.