Chemical-Assisted CO₂ Water-Alternating-Gas Injection for Enhanced Sweep Efficiency in CO₂-EOR

Area of Science:

• Petroleum Engineering
• Carbon Capture and Utilization
• Reservoir Engineering

Background:

• CO2-enhanced oil recovery (CO2-EOR) is vital for CO2 utilization and sequestration, offering carbon reduction benefits.
• Low CO2 viscosity and reservoir heterogeneity cause early gas breakthrough, reducing efficiency.
• Water-alternating-gas (WAG) injection mitigates these issues but faces challenges in heterogeneous/fractured reservoirs.

Purpose of the Study:

• To provide an updated and comprehensive review of CO2-WAG flooding techniques.
• To incorporate the latest advancements for enhanced sweep efficiency in CO2-EOR.
• To serve as a reference for applying and advancing CO2-EOR in challenging reservoirs.

Main Methods:

• Review of experimental studies.
• Analysis of simulation data.
• Inclusion of pore-scale modeling insights.

Main Results:

• CO2-WAG injection improves sweep efficiency and mitigates gas breakthrough.
• Challenges in heterogeneous/fractured reservoirs include channeling and low sweep efficiency.
• Remedial measures and operational strategies for WAG projects are discussed.

Conclusions:

• CO2-WAG is a promising technique for efficient CO2-EOR, utilization, and sequestration.
• Addressing reservoir heterogeneity and mobility control is key to maximizing CO2-WAG effectiveness.
• This review guides future research and application of CO2-EOR in complex geological formations.