Life cycle assessment and sustainability enhancement of closed-loop carbon dioxide enhanced oil recovery: Field-scale evaluation in Qatar's Dukhan Reservoir

This study presents a comprehensive environmental evaluation of direct CO₂ injection for Enhanced Oil Recovery (EOR) in the Dukhan Field, Qatar, using a gate-to-gate Life Cycle Assessment (LCA) coupled with an energy optimisation framework. Four operational years (Year 1, 8, 19, and 21) were analysed to capture the system's transition from external CO₂ sourcing to full internal recycling. Simulations incorporated the recovery of hydrocarbon-rich fuel gases from the capture and purification units, which were utilised in an on-site Combined Heat and Power (CHP) system operating at 55% efficiency. In Year 1, the CHP unit generated 22.2 million GJ of electricity, offsetting 62.5% of the system's total energy demand (35.5 million GJ). By Year 19, internal energy offset declined to 45.0% due to reduced fuel gas availability, and in Year 21, the fully closed-loop operation required complete reliance on external electricity. Environmental impacts were assessed using the ReCiPe Midpoint (H) 2016 method across 15 impact categories. Global warming potential (GWP100) decreased from 2.00 × 10¹⁰ kg CO₂-eq in Year 1 to 1.20 × 10⁹ kg CO₂-eq in Year 21, with a 16% reduction observed in Year 1 under the fuel gas recovery scenario. This study underscores the environmental and operational advantages of integrating fuel gas recovery and CO₂ recycling. It demonstrates that co-optimising energy and carbon loops can improve lifecycle performance, reduce reliance on fossil-based grid electricity, and support sustainable CO₂-EOR deployment under region-specific constraints.