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 x 10(10) kg CO2-eq in Year 1 to 1.20 x 10(9) 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.