Aquifer-on-a-chip: understanding pore-scale salt precipitation dynamics during CO2 sequestration

Area of Science:

• Geosciences
• Chemical Engineering
• Environmental Science

Background:

• Carbon dioxide (CO2) sequestration in saline aquifers is a key carbon management strategy.
• Salt precipitation during CO2 injection can reduce storage capacity and injectivity.
• Understanding pore-scale salt formation dynamics is crucial for predicting long-term CO2 storage performance.

Purpose of the Study:

• To develop and utilize a lab-on-a-chip approach to investigate pore-scale salt precipitation during CO2 sequestration.
• To characterize the mechanisms and morphology of salt formation at the microfluidic level.
• To quantify the impact of salt precipitation on porosity and CO2-brine interface dynamics.

Main Methods:

• Development of a microfluidic device mimicking geological formations for studying three-phase flow (CO2, brine, salt).
• In-situ visualization and tracking of CO2 (gas), brine (liquid), and salt (solid) phases within microfluidic networks.
• Analysis of salt formation morphology, spatial distribution, and temporal evolution.

Main Results:

• Observed porosity decreases of approximately 20% due to salt formation, consistent with core flood studies.
• Identified two dominant salt formation types: early-forming bulk crystals in trapped brine and late-forming polycrystalline aggregates at the CO2-brine interface.
• Measured a salt precipitation front velocity of about 2% of the superficial CO2 velocity.

Conclusions:

• Salt precipitation significantly impacts pore structure, leading to pore blockage and reduced storage capacity.
• The observed salt formation mechanisms provide insights into the challenges of long-term CO2 sequestration in saline formations.
• Lab-on-a-chip technology offers a valuable tool for studying complex geochemical processes at the pore scale.