Evaluating the Climate Benefits of CO₂-Enhanced Oil Recovery Using Life Cycle Analysis

Abstract

This study uses life cycle analysis (LCA) to evaluate the greenhouse gas (GHG) performance of carbon dioxide (CO2) enhanced oil recovery (EOR) systems. A detailed gate-to-gate LCA model of EOR was developed and incorporated into a cradle-to-grave boundary with a functional unit of 1 MJ of combusted gasoline. The cradle-to-grave model includes two sources of CO2: natural domes and anthropogenic (fossil power equipped with carbon capture). A critical parameter is the crude recovery ratio, which describes how much crude is recovered for a fixed amount of purchased CO2. When CO2 is sourced from a natural dome, increasing the crude recovery ratio decreases emissions, the opposite is true for anthropogenic CO2. When the CO2 is sourced from a power plant, the electricity coproduct is assumed to displace existing power. With anthropogenic CO2, increasing the crude recovery ratio reduces the amount of CO2 required, thereby reducing the amount of power displaced and the corresponding credit. Only the anthropogenic EOR cases result in emissions lower than conventionally produced crude. This is not specific to EOR, rather the fact that carbon-intensive electricity is being displaced with captured electricity, and the fuel produced from that system receives a credit for this displacement.

Environmental and Operational Performance of CO2-EOR as a CCUS Technology: A Cranfield Example with Dynamic LCA Considerations

“…Most carbon lifecycle analyses use an average for EOR/storage efficiency in their calculations, but as demonstrated here, CO2 utilization rates vary significantly throughout the operation; such simplifications affect carbon balance results. Cooney et al [13], acknowledged this as a potential improvement, which we have accomplished in this study. A better indicator of the efficiency of the CO 2 -EOR floods are the CO 2 utilization rates ( Figure 5), which refer to the volume of CO 2 that needs to be injected to produce one barrel of oil.…”

“…Most carbon lifecycle analyses use an average for EOR/storage efficiency in their calculations, but as demonstrated here, CO 2 utilization rates vary significantly throughout the operation; such simplifications affect carbon balance results. Cooney et al [13], acknowledged this as a potential improvement, which we have accomplished in this study.…”

“…We assumed a maximum pipeline transportation distance of 300 miles from the Cranfield field to the closest concentration of refineries in the USA This cluster refines about 75% of the total crude oil processed in the USA Gulf Coast area. Based on Cooney et al [13], we assumed that USA crude oil is transported from the field to the refineries with an energy intensity of 260 BTU/tonne-mile or 189 J/kg-Km. We also assumed that this energy is 100% supplied by the local grid (SRMV).…”

Life Cycle CO2 Emission Estimation of CCS-EOR System Using Different CO2 Sources

“…This study assessed the overall life cycle emissions associated with sequestration via CO 2 -flood EOR under a number of different scenarios and explored the impact of various methods for allocating CO 2 system emissions and the benefits of sequestration [15]. Hussain et al (2013) and Cooney et al (2015) used hypothetical reservoir models to evaluate GHG emissions for CO 2 -EOR based on various CO 2 sources, including conventional CO 2 sources (e.g., natural source, coal synthetic natural gas (SNG) plant) and alternative CO 2 sources (e.g., coal IGCC, switch grass IGCC, natural gas combined cycle (NGCC), and biogas NGCC). And they also carried out sensitivity analysis for the range of EOR parameters [16][17].…”

“…Hussain et al (2013) and Cooney et al (2015) used hypothetical reservoir models to evaluate GHG emissions for CO 2 -EOR based on various CO 2 sources, including conventional CO 2 sources (e.g., natural source, coal synthetic natural gas (SNG) plant) and alternative CO 2 sources (e.g., coal IGCC, switch grass IGCC, natural gas combined cycle (NGCC), and biogas NGCC). And they also carried out sensitivity analysis for the range of EOR parameters [16][17]. Hussain et al (2013) used a process lifecycle inventory (LCI) to compare the lifecycle greenhouse gas (GHG) emissions of enhanced oil recovery (EOR) operations using different sources for CO 2 and to non-CO 2 EOR methods [16].…”