CO2-Enhanced oil recovery in unconventional reservoirs: Motivation, mechanisms, factors, challenges and methods

Abstract

CO₂-Enhanced oil recovery and carbon storage in ultra-tight shale reservoirs are governed by multiscale interactions spanning molecular thermodynamics to reservoir engineering. Key mechanisms include CO₂-induced oil swelling and pressure mobilization, diffusion-dominated hydrocarbon transport, viscosity reduction via hydrocarbon plasticization, and competitive adsorption displacing methane from organic surfaces. These processes synergize temporally: Swelling and diffusion dominate early-stage recovery, while viscosity reduction and miscibility prevail later, enhanced by cyclic injection strategies to overcome fracture-limited flow geometries. Supercritical CO₂ optimizes extraction efficiency and pore penetration but elevates operational risks through potential fracture leakage. Challenges persist in reconciling nanoconfinement-altered phase behavior, wettability shifts from carboxylate formation, and adsorption hysteresis impacting long-term storage stability. Emerging machine learning frameworks integrate dimensionless parameters to optimize injection protocols, yet geochemical-geomechanical feedbacks demand dynamic coupling of reactive transport models with fracture stability analyses. Advancing CO₂-EOR-storage co-optimization requires multiscale model integration, combining in-situ spectroscopic characterization of interfacial phenomena with sensor-driven monitoring of plume dynamics. By resolving molecular-to-reservoir asymmetries, shale’s inherent complexity can be leveraged for sustainable energy transitions, balancing hydrocarbon recovery with secure carbon sequestration through science-informed engineering innovations.

Document Type:  Perspective

Cited as: Zhang, D., Zhang, T., He, S., Zhu. C., Gong, L. CO₂-Enhanced oil recovery in unconventional reservoirs: Motivation, mechanisms, factors, challenges and methods. Computational Energy Science, 2025, 2(1): 1-6. https://doi.org/10.46690/compes.2025.01.01

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