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Nanopore Processes - Thrust Area 2

Synopsis

One of our major scientific challenges is to understand the behavior of carbon dioxide-rich aqueous solutions confined at high temperature and pressure in nanoporous matrices under geologic sequestration conditions.  The goal of research under Thrust Area 2 is to provide a fundamental understanding of these confined carbon dioxide-aqueous solution mixtures using advanced experimental and computational methodologies to probe fluid behavior from molecular to pore scales.

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Quartz-Brine Image

Leads and Contacts - Thrust Area 2

Ian Bourg

Ian Bourg
Thrust Area 2 Lead

Background and Significance

Carbon dioxide is a gas under ambient conditions, but under the temperature and pressure conditions of geologic sequestration, it becomes a supercritical fluid with a density and viscosity somewhat lower than those of liquid water or saline aqueous solutions. When dissolved in water, supercritical carbon dioxide produces an acidic solution that is very corrosive to rock-forming minerals.  Adding to this complexity, deep natural waters are typically not pure liquids, but instead are brines having salinities many times greater than seawater. Thus the physicochemical properties of carbon dioxide-aqueous solution mixtures will strongly affect the behavior of carbon dioxide plumes injected into terrestrial geologic formations.

The geologic sequestration of supercritical carbon dioxide is inherently a multiscale process (see the figure above).  In the initial stages of injection (decadal time scales), the supercritical fluid must flow easily and uniformly (i.e. without long “fingers”) into the pore space of the host rock. Thereafter, it must be prevented from escaping into the atmosphere or contaminating shallow aquifers by a low-permeability, nanoporous caprock which provides a reliable seal over decadal to centurial time scales.  The relatively low interfacial tension of supercritical carbon dioxide-natural water mixtures may allow the injected carbon dioxide to escape through the confining caprocks or aquitards by buoyancy-driven advection. Interfacial properties also will determine the importance of “capillary trapping” by the caprock at the trailing edge of flowing carbon dioxide plumes and they may control the uptake of water and ions through the supercritical carbon dioxide-natural water interface which, in turn, will impact the reactivity of carbon dioxide with host-rock minerals on millennial time scales. Moreover, as the relatively nonwetting carbon dioxide fluid is displaced into pores previously filled with subsurface brine, residual saline aqueous films are expected to remain over time scales that are currently unknown. These thin films of native fluids coating the caprock and host-rock minerals impose diffusive interfaces between the invading fluid and the minerals, thus mediating the early stages of carbon dioxide-mineral interactions. Over larger than pore-scale distances, the mechanical properties of thin films along with capillary forces will control the pore-scale advance of fluid fronts and hence the evolution of invading-fluid flow paths. Thus understanding the behavior of trapped residual brine films is central to controlling the sequestration process over the full spectrum of critical length scales from molecular to reservoir.

Approach

TBD

Expected Outcomes

TBD

Research Team

The Nanopore Processes Research Team performs laboratory experiments and molecular simulations on carbon dioxide-aqueous brine mixtures at high temperature and pressure in porous media relevant to geological sequestration.  The principal research tasks to be undertaken by the team during the first year or two of the Center's operation are identified in a set of downloadable slides.

  • Ian Bourg, LBNL
  • Ariel Chialvo, ORNL
  • David Cole, ORNL
  • Mirek Grusziewicz, ORNL
  • Gernot Rother, ORNL
  • Garrison Sposito, LBNL
  • Tetsu Tokunaga, LBNL
  • Jiamin Wan, LBNL