Heterogeneity Driven Trapping at the Pore-Network Scale in Edwards Brown Dolomite

Area of Science:

• Geological Carbon Storage
• Pore-Scale Physics
• Reservoir Engineering

Background:

• Residual trapping of CO2 is crucial for geological storage stability but challenging to model at field scales.
• Capillary trapping, influenced by pore-scale heterogeneity and capillary entry pressures, significantly impacts CO2 plume migration.
• Current continuum-scale models struggle to integrate the effects of micron-to-centimeter scale pore heterogeneity on trapping efficiency.

Purpose of the Study:

• To investigate the impact of pore-scale heterogeneity, specifically capillary barriers, on CO2 trapping efficiency and plume migration.
• To quantify how pore connectivity and throat geometry influence capillary entry pressures and snap-off mechanisms.
• To assess the necessity of incorporating pore-scale heterogeneity effects into upscaled models for heterogeneous formations.

Main Methods:

• Conducted flow experiments using brine and decane under capillary-dominated conditions (Ca = 2.6 × 10^-7).
• Acquired time-resolved 3D micro-CT images at 5.6 μm voxel size on a 12 mm by 60 mm rock sample.
• Analyzed segmented volumes using pore-network analysis and ganglia volume/count analysis to quantify trapped volumes.

Main Results:

• A downstream low-porosity region acted as a partial capillary barrier, remaining brine-saturated during decane injection.
• Pore-network analysis revealed limited connectivity (coordination number ~2), with over 30% of pores connected by two or fewer throats.
• Capillary barriers demonstrated enhanced trapping, with negligible displacement of the mobile phase and elevated trapped ganglia volume and count post-imbibition.

Conclusions:

• Capillary barriers significantly increase fluid immobilization while reducing accessible pore volume in heterogeneous formations.
• The presence of capillary barriers influences CO2 plume migration pathways, leading to enhanced trapping.
• Upscaled models for geological storage in heterogeneous formations must capture the effects of pore-scale capillary barriers for accurate predictions.