Comparative lifecycle inventory (LCI) of greenhouse gas (GHG) emissions of enhanced oil recovery (EOR) methods using different CO2 sources

Abstract

This study uses a process lifecycle inventory (LCI) to compare the lifecycle greenhouse gas (GHG) emissions of enhanced oil recovery (EOR) operations using different sources for CO2 and to non-CO2 EOR methods. All EOR techniques were compared to the base case of natural-source CO2-EOR, which had net emissions of 0.52±0.03 metric tons of CO2-e per barrel of oil recovered (t/bbl) (85.1±4.9gCO2-e/MJ oil (g/MJ)), the same as the net emissions of 0.52±0.02t/bbl (84.3±3.0g/MJ) when using CO2 derived from a coal-fueled synthetic natural gas (SNG) plant. Net emissions were lowered to 0.36±0.03t/bbl (58.5±5.2g/MJ) for EOR using CO2 derived from a coal-fed Integrated Gasification Combined Cycle (IGCC) plant. Net emissions were further reduced to 0.18±0.11t/bbl (28.6±18.7g/MJ) using switchgrass grown on marginal land in an IGCC plant. Similar to coal, net emissions were 0.34±0.03t/bbl (55.3±5.5g/MJ) for EOR using CO2 derived from a Natural Gas Combined Cycle (NGCC) plant, and 0.39±0.03t/bbl (63.3±4.4g/MJ) when using livestock manure biogas for NGCC. Net emissions of methane- and nitrogen-EOR were 10–15% greater than for natural-source CO2-EOR. For the allocations used in this study, all sources of CO2 derived from IGCC or NGCC plants resulted in between about 25% and 60% lower net CO2-e emissions per barrel of oil recovered compared to natural-source CO2-EOR, and were also approximately 25–60% lower than average domestic U.S. oil lifecycle emissions of 0.50±0.02t/bbl (82.4±2.5g/MJ). These results suggest that coal and biomass IGCC CO2-EOR, as well as natural gas and biogas NGCC CO2-EOR, may be alternatives for reducing GHG emissions associated with fossil fuel use during the slow transition from fossil fuels to other energy sources.