Abhijit Chaudhuri

Bio: Abhijit Chaudhuri is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Concentration polarization & Convection. The author has an hindex of 14, co-authored 44 publications receiving 656 citations. Previous affiliations of Abhijit Chaudhuri include Indian Institute of Science & University of Colorado Boulder.

Alteration of fractures by precipitation and dissolution in gradient reaction environments: Computational results and stochastic analysis

Abstract: [1] Precipitation and dissolution reactions within fractures alter apertures, which in turn affects their flow and transport properties. Different aperture alteration patterns occur in different flow and reaction regimes, and they are also influenced by preferential flow resulting from spatial variations in the aperture. We consider the alteration of variable-aperture fractures in gradient reaction regimes, where fluids are in chemical equilibrium with a mineral everywhere but precipitation and dissolution are driven by solubility gradients associated with temperature variations. The temperature field is defined by a geothermal gradient corresponding to a conduction-dominated heat transfer regime. Monte Carlo simulations on computer-generated aperture fields vividly illustrate pattern formation resulting from two-way feedback between fluid flow and reactive alteration. In dissolution-controlled systems, distinct dissolution channels develop along the dominant flow direction, while elongated precipitate bodies form perpendicular to the mean flow direction in precipitation-controlled systems. Aperture variability accelerates the increase and decrease of effective transmissivity by dissolution and precipitation, respectively. The dominance of precipitation versus dissolution is determined by the angle between the mean hydraulic gradient and solubility/temperature gradient. Development of pronounced anisotropy with oriented elongate features is the key feature of aperture alteration in gradient reaction regimes. A stochastic analysis is developed, which consistently predicts general trends in the aperture field during reactive alteration, including the mean, variance, and spatial covariance structure. Our results are relevant to understanding the long-term diagenetic evolution of fractures in conduction-dominated heat transfer regimes and related problems such as emplacement of ocean bed methane hydrates.

Early-stage hypogene karstification in a mountain hydrologic system: A coupled thermohydrochemical model incorporating buoyant convection

Abstract: [1] The early stage of hypogene karstification is investigated using a coupled thermohydrochemical model of a mountain hydrologic system, in which water enters along a water table and descends to significant depth (∼1 km) before ascending through a central high-permeability fracture. The model incorporates reactive alteration driven by dissolution/precipitation of limestone in a carbonic acid system, due to both temperature- and pressure-dependent solubility, and kinetics. Simulations were carried out for homogeneous and heterogeneous initial fracture aperture fields, using the FEHM (Finite Element Heat and Mass Transfer) code. Initially, retrograde solubility is the dominant mechanism of fracture aperture growth. As the fracture transmissivity increases, a critical Rayleigh number value is exceeded at some stage. Buoyant convection is then initiated and controls the evolution of the system thereafter. For an initially homogeneous fracture aperture field, deep well-organized buoyant convection rolls form. For initially heterogeneous aperture fields, preferential flow suppresses large buoyant convection rolls, although a large number of smaller rolls form. Even after the onset of buoyant convection, dissolution in the fracture is sustained along upward flow paths by retrograde solubility and by additional “mixing corrosion” effects closer to the surface. Aperture growth patterns in the fracture are very different from those observed in simulations of epigenic karst systems, and retain imprints of both buoyant convection and preferential flow. Both retrograde solubility and buoyant convection contribute to these differences. The paper demonstrates the potential value of coupled models as tools for understanding the evolution and behavior of hypogene karst systems.

Buoyant convection resulting from dissolution and permeability growth in vertical limestone fractures

Abstract: [1] Upward flow through vertical fractures in limestone formations under a geothermal gradient favors dissolution and permeability growth. We investigate the transition from conductive and forced convective regimes to instability and buoyant convection as a result of permeability growth. The onset time for instability and roll height at onset depend on the initial aperture and driving pressure. A modified Rayleigh number criterion is proposed, which provides a unified interpretation of the instability across a wide range of initial aperture and driving pressure. Interaction between buoyant convection and aperture alteration leads to narrow upward flow paths supporting dissolution and precipitation in surrounding downward flow regions.

Porosity–Permeability Relations for Evolving Pore Space: A Review with a Focus on (Bio-)geochemically Altered Porous Media

Abstract: Reactive transport processes in a porous medium will often both cause changes to the pore structure, via precipitation and dissolution of biomass or minerals, and be affected by these changes, via changes to the material’s porosity and permeability. An understanding of the pore structure morphology and the changes to flow parameters during these processes is critical when modeling reactive transport. Commonly applied porosity–permeability relations in simulation models on the REV scale use a power-law relation, often with slight modifications, to describe such features; they are often used for modeling the effects of mineral precipitation and/or dissolution on permeability. To predict the reduction in permeability due to biomass growth, many different and often rather complex relations have been developed and published by a variety of authors. Some authors use exponential or simplified Kozeny–Carman relations. However, many of these relations do not lead to fundamentally different predictions of permeability alteration when compared to a simple power-law relation with a suitable exponent. Exceptions to this general trend are only few of the porosity–permeability relations developed for biomass clogging; these consider a residual permeability even when the pore space is completely filled with biomass. Other exceptions are relations that consider a critical porosity at which the porous medium becomes impermeable; this is often used when modeling the effect of mineral precipitation. This review first defines the scale on which porosity–permeability relations are typically used and aims at explaining why these relations are not unique. It shows the variety of existing approaches and concludes with their essential features.