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Microfluidics Laboratory: Micromodel Studies of
CO2 Pore-Scale Trapping Processes

Key laboratory capabilities include:

  • Control of pore network structure through precision microfabrication
  • Use of enhanced imaging of micromodels using solvatochromic dyes
  • Control of surface wettability
  • Image analysis techniques for quantitative measurement of saturations and interfacial areas.

To improve our understanding of geological carbon sequestration, pore-scale experimental and numerical studies of processes related to caprock-sealing efficiency and trapping are needed. Caprock-sealing efficiency is a measure of the capillary pressure at the caprock/reservoir interface that needs to be exceeded before supercritical carbon dioxide (scCO2) can move into the caprock. The major trapping mechanisms include storage of free-phase gas through hydrodynamic and capillary trapping, dissolution in formation brines, and mineral trapping through geochemical reactions. Many of these trapping processes are controlled by pore-scale mechanisms that can best be understand by pore-scale experiments and simulations.

PNNL has developed a high-pressure, pore-scale flow and transport capability for highly controlled displacement and dissolution experiments involving brine/scCO2 fluid pairs. The laboratory uses centimeter-scale microfluidics devices with porous structures etched into silicon wafers to study critical pore-scale multi-fluid flow processes.

High-pressure micromodel chamber

High-pressure micromodel chamber used for multiphase flow experiments with scCO2. (Photo credit: Mart Oostrom, PNNL.) Enlarged View

network geometries

An example micromodel system with two different pore network geometries corresponding to relatively higher and lower permeabilities.
Enlarged View

Experiments conducted under a wide range of conditions have been used to quantify distinct displacement regimes (stable displacement, viscous fingering, capillary fingering) and their impacts on effective flow properties. Micromodel experiments and related analyses are being used to guide modeling at larger scales. For example, DeHoff et al. (2012) demonstrated that under unstable displacement conditions, the commonly used approach that couples constitutive relationships of relative permeability, saturation, and capillary pressure fails to provide good predictions. However, an approach that decouples relative permeability relationships can accurately predict average saturations. This result has concrete implications for how field-scale reservoir modeling should be performed under different injection conditions and will lead to improvements in field-scale STOMP modeling.

pattern of liquid CO2
Variations in the pattern of liquid CO2 displacing water in a dual-permeability pore network under three different flow rates.

Geological Carbon Storage Research at PNNL

Energy and Environment Directorate