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Description
CO2 injection into geological formations is considered as technologically advanced and economically feasible approach that combines both CO2 sequestration and enhanced oil recovery (EOR). The absorption- and diffusion processes at the CO2-oil interface (under reservoir conditions) plays an integral role in governing key physico-chemical properties such as volume increase, miscibility, density change, diffusion, and interfacial tension and their complex interrelationship.
We proposed a conceptual model that accounts for CO2 density fluctuations in the critical range (31°C, 7.38 MPa) and explains the time-dependent oil volume increase under specific thermodynamic conditions. Our micro-CT experiments validate the model and demonstrates that the oil volume increase in the non-critical pressure range (< 6 MPa) is a surface effect with limited penetration depth, controlled by the lighter/short-chain alkanes in the oil. The oil swelling increase significantly from 1.8 mm to 14 mm by varying the composition of lighter components (C1-C10) in the oil from 20 % to 100 %, respectively. An ordered short-chain alkane-CO2-alkane structure forms at the CO2-oil interface through CO2 binding bridges subsequently enhancing oil volume until the equilibrium is achieved. In the critical pressure range (6 - 8 MPa), oil volume increase is caused by the mixing of liquid CO2 droplets in the oil phase.
Concurrently, we conducted independent pressure decay analysis, evaluated the key kinetic parameters, and studied the CO2 diffusion processes in the oil phase. Our conceptual model shows an excellent agreement (relative error ≤ 0.5 %) with the pressure-decay experimental results for both the equilibrium- and non-equilibrium model, and a diffusion coefficient in the range of 10−7 m2/s indicates a fast CO2 mass transfer process.
| References | Geistlinger, H., & Zulfiqar, B. (2024). Absorption and diffusion process at the CO2-decane interface considering density fluctuations near the critical CO2 point. Surfaces and Interfaces, 105520. |
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| Country | Germany |
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