Research: Thermodynamics - CO2 Sequestration - Geochemistry - Metamorphic Petrology

 

I am currently a NERC-funded research associate involved in the CRIUS project (Carbon Research Into Underground Storage). I have been working in the team of Mike Bickle since January 2009, starting within the Marie Curie GRASP program (Greenhouse-gas Removal Apprenticeship & Student Program).

My research is focused on modelling gas-rock-fluid interactions to better understand metamorphism and mineral reactivity at low temperatures (i.e., under Greenschist Facies conditions).

Evolution of the water content (dashed line) of clay and total volume of solids (continuous line) as a function of temperature and pressure, calculated by Vidal and Dubacq (2009) for a Na-rich clayey rock The water content includes both structural and interlayer water of clay minerals.

Studying phase relations of minerals, aqueous species and gaseous phases is necessary to predict the fate of carbon dioxide in geological reservoirs on both long-term and short-term scales, e.g. for Enhanced Oil Recovery, as well as to estimate the pressure - temperature conditions of crystallization of mineralogical assemblages. I mainly use macroscopic thermodynamics to predict and quantify dissolution / crystallization processes.

A thin section of metapelite analyzed by electronic microprobe, the corresponding Si content per formula unit in chlorites and phengites (calculated with the method of De Andrade et al. 2006) and temperatures of crystallization for phengites (Dubacq et al. 2010).

Working with natural systems is a challenging task for it requires dealing with highly variable concentrations of aqueous species (from fresh waters to brines) and complex minerals like phyllosilicates (clay minerals, micas, chlorites, serpentines), carbonates, feldspars, etc. The macroscopic thermodynamic properties of natural low-temperature systems are currently poorly constrained, mainly because sluggishness of reaction often precludes short time-scale experiments and implies considering local thermodynamic equilibrium rather than global equilibrium. There is also a desperate need for experimental data in some systems that have not been completely studied. My work consists in linking available experimental results, observations in natural systems and theoretical considerations to build thermodynamic models.

Phase diagram for CO2-H2O mixtures, points are experimental results and lines are calculated with our model compatible with THERMOCALC (submitted to GCA).

 

Mike Bickle pointing at sandstones bleached by CO2-rich fluids in Green River, Utah.

I am also interested in recent methods of estimation of thermodynamic properties, and especially atomistic simulations based on force fields, which bring significant insight and reliable constraints on minerals stability and activity-composition relations in complex mineralogical systems; in short, these microscopic-scale methods allow calibrating missing macroscopic-scale thermodynamic properties.

I am a geologist by training and keep enjoying field trips in cold, wet, polluted and preferably mountainous environments. Applying models to real systems is important to me! As well as teaching and working with students. I work with research teams in Paris (P. Agard, ISTeP) and Grenoble (O. Vidal, ISTerre). 

 

 

 

 

Publications

  (e-mail me for reprints)

   Dubacq, B., Bickle, M., Kampman, N., Wigley, M., Ballentine, C.J., Sherwood Lollar, B. (accepted, in revision). Noble gas and carbon isotopic evidence for CO2-driven silicate dissolution in a recent natural CO2 field. Earth and Planetary Science Letters

  Tipper, E.T., Calmels, D., Gaillardet, J., Louvat, P., Capmas, F., Dubacq, B. (in press). Positive correlation between Li and Mg isotope ratios in the river waters of the Mackenzie Basin challenges the interpretation of apparent isotopic fractionation during weathering. Earth and Planetary Science Letters

  Wigley, M., Kampman, N., Dubacq, B., Bickle. M. (in press). Fluid-Mineral Reactions and Trace Metal Mobilization in an Exhumed Natural CO2 Reservoir, Green River, Utah. Geology (link)

  Plunder, A., Agard, P., Dubacq, B., Chopin, C., Bellanger, M. (2012). How continuous and precise is the record of P-T paths? Insights from combined thermobarometry and thermodynamic modelling into subduction dynamics (Schistes Lustrés, W. Alps). Journal of Metamorphic Geology, 30, 323-346 (link)

  Ganne, J., De Andrade, V., Weinberg, R., Vidal, O., Dubacq, B., Kagambega, N., Naba, S., Baratoux, L., Jessell, M., Allibon, J. (2012). Modern-style plate subduction preserved in the Palaeoproterozoic West Africa Craton. Nature Geoscience, 5, 60-65 (link)

  Dubacq, B., Vidal, O., Lewin E. (2011). Atomistic investigation of the pyrophyllitic substitution and implications on clays stability. American Mineralogist, 96, 241-249 (link)

  Vidal, O., Dubacq, B., Lanari, P. (2010). Comment on "The Role Of H3O+ In The Crystal Structure of Illite" by F. Niéto, M. Melini, and I. Abad. Clays and Clay Minerals, 58, 717-720 (link)

  Agard, P., Searle, M.P., Alsop, G.I., Dubacq, B. (2010). Crustal stacking and expulsion tectonics during continental subduction: P-T deformation constraints from Oman. Tectonics, 29, TC5018 (link)

  Dubacq, B., Vidal, O., De Andrade, V. (2010). Dehydration of dioctahedral aluminous phyllosilicates: thermodynamic modelling and implications for thermobarometric estimates. Contributions to Mineralogy and Petrology, 159, 159-174 (link)

  Vidal, O., Dubacq, B. (2009). Thermodynamic modelling of clay dehydration, stability and compositional evolution with temperature, pressure and H2O activity. Geochimica et Cosmochimica Acta, 73, 6544 - 6564 (link)

 

The Siberian traps: basaltic lavas on top of sandstones (white) and coal-rich layers (black).   Nickel smelters around Norils'k, Siberia. There are no big trees because they don't grow very well when fed with acid rain and heavy metals. 


Publications: 2006-Present

Last updated on 11-Apr-12 17:53