X-ray Microtomography of Intermittency in Multiphase Flow at Steady State Using a Differential Imaging Method

Area of Science:

• Geosciences
• Petroleum Engineering
• Fluid Dynamics

Background:

• Understanding multiphase flow in porous media is crucial for oil recovery and carbon sequestration.
• Pore-scale fluid distribution significantly impacts macroscopic flow properties like relative permeability.

Purpose of the Study:

• To investigate the impact of flow rate on pore-scale fluid distribution during brine and decane coinjection in Bentheimer sandstone.
• To elucidate flow regimes and dynamic connectivity of non-wetting phases at different capillary numbers (Ca).

Main Methods:

• Developed a differential imaging technique to visualize fluid distribution at the pore scale.
• Conducted experiments at two capillary numbers (3.0 × 10⁻⁷ and 7.5 × 10⁻⁶) across various fractional flows.
• Measured pressure drops using high-precision sensors and analyzed fluid occupancy using image histogram distribution.

Main Results:

• At low Ca, fluids flowed in stable, connected subnetworks, aligning with conventional theory.
• At high Ca, observed intermittent occupancy of pore space by oil and brine, crucial for explaining dynamic oil phase connectivity.
• Non-wetting phase pathways did not always span the core, indicating segmented flow at higher Ca.

Conclusions:

• The study reveals distinct flow regimes at different capillary numbers, challenging conventional assumptions at higher flow rates.
• Intermittent fluid occupancy is a key mechanism for dynamic connectivity of non-wetting phases in porous media.
• Experimental results at the mm-scale show good agreement with literature data from cm-scale samples, validating the method.