Current Research

Please see my recent publication list in my CV for more recent research.

Recent Research

Computational Porous Media Flows, Transport, and Reactions

I have developed a two-dimensional, time-dependent code to model flow and chemical reactions in a fractured and porous medium. Both equilibrium and nonequilibrium reactions are modeled using real thermodynamic data. I am examining the effect of reaction kinetics on changes of porosity with time. Working with Antonio Lasaga and Danny Rye, we have discovered that oscillatory thermal boundary instabilities have a profound influence on the saturation state and precipitation history. Zonation of mineral grains can often be expected down to the smallest observable scale. Significant portions of crustal fluids violate assumptions based on equilibrium when real kinetics are incorporated into models. For example, near the ends of high permeability zones, one can observe downwelling oversaturated fluids and oversaturated fluids moving toward higher temperatures, both contrary to the conventional wisdom based on equilibrium. Potential applications for such models are broad, and encompass a variety of geological problems, from ore deposits, to nuclear waste contamination, to deposits in hydrothermal zones. Ultimately, we hope to couple this code to a physical erosion code (discussed below).

Working in collaboration with Mike Oristaglio's group at Schlumberger-Doll Research in Ridgefield, Connecticut, I have developed a Lagrangian particle tracking scheme for solving the advection of gas/oil/water interfaces associated with secondary oil recovery. The interface motion induces measurable changes in the gravity field. We hope to compare the results of such numerical simulations with field observation of microgravity changes in horizontal wells.

Some Abstracts

Kinetic Control of Contact Metamorphism Bolton, E.W., A. Luettge, D.M. Rye, and A.C. Lasaga, Geologic Society of America, Abstracts with Programs, vol. 30, no. 7, p. A-280, 1998.

We build upon the thermodynamic theory of metamorphic reactions to create a model of kinetically controlled metamorphism that extends the work of Rice and Ferry (1982), Walther and Wood (1994), and Lasaga and Rye (1993). For conditions of contact metamorphism, competing processes are assessed as to their relative importance, including rates of cooling, heating, fluid flow, reaction kinetics, and heats of reaction. This two-dimensional model of a cooling pluton initially in contact with a dolomite/quartz matrix naturally ranges from near equilibrium to far from equilibrium evolution depending on a number of critical factors, such as permeability, the form of the kinetic rate law, mineral surface areas, and nucleation barriers. Endmembers concepts such as external fluid control vs. buffering along equilibrium curves are special limits for rapid kinetics but differing flow rates. Overstepping of equilibrium curves is especially pronounced with nonlinear kinetic rate laws. Similar mineral assemblages can be created by very different T-X_CO₂ paths, indicating that observables from the field will not necessarily identify the path which created them. Our current model solves for transport and reactions at metamorphic conditions (with supercritical H₂O-CO₂ mixtures) in a two-dimensional heterogeneous permeability medium. The kinetic formulation has rates which depend on Gibbs free energy and temperature. Thermodynamic databases are used to calculate the Gibbs free energy at metamorphic conditions. Such calculations use fugacity and equation of state estimates for H₂O-CO₂ mixtures. An assessment is made at each local node for which phases are present and which reactions are possible on an energetic basis. Darcy velocities are calculated directly from the density. We will present results for the mineral system CaO-SiO₂-MgO-H₂O-CO₂ in the temperature range between 450 to 700C at a pressure of 3 kbar. We consider both stable and metastable metamorphic reactions at their local p-T conditions. This model has applicability to a large number of geologic environments.

Kinetic isotope effects: The competition of diffusion and recrystalization, E.W. Bolton, A.C. Lasaga, D.M. Rye, and S. Chakraborty, Geologic Society of America, Abstracts with Programs, vol. 29, no. 6, p. A-25, 1997.

A new numerical model has been created which is capable of following the isotopic evolution of mineral grains in contact with fluids including the effects of both diffusion and dissolution / precipitation. The model addresses kinetic isotope effects in both open and closed systems of various spatial dimensions. For closed systems, we compare model results with the experiments of Burch and Cole on oxygen isotope changes in calcite and water. We also examine isotopic evolution during imposed thermal histories in 1D flow-through systems. The model allows for various mineral types and size fractions and solves for diffusion within spherical grains that are simultaneously growing or dissolving. Exchange of isotopes between grains and the fluid occurs due to diffusion, dissolution, and precipitation. The moving grain boundaries require special numerical treatment of the finite difference model with variable grid spacing. At the surface of the grains we presently assume isotopic equilibrium between the fluid and the grains. The required temperature-dependent diffusion coefficients within the grains and the isotopic fractionation factors for the grain surfaces are known for a variety of minerals. In one or more dimensions, we also solve fluid and solute transport equations with advection, diffusion, and source/sink terms at the fluid/grain boundaries. The solution of such a system will allow a fully consistent and simultaneous calculation of both isotopic and coupled flow and transport, when this model is coupled to the other models of reactive flow and transport. This represents a major step forward, as we will be able to link the kinetics of mineral exchange with that of isotopic exchange. The results with both diffusion and dissolution / precipitation acting in combination are quite different from a simple addition of their individual effects, which underscores the importance of this unified approach.
Edward Bolton
Department of Geology and Geophysics
Yale University
P.O. Box 208109
New Haven, CT 06520-8109
U.S.A.

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Last updated: 11 August 2005