Abstract
The annual global growth rate for geothermal power generation between 2021 and 2030 is targeted to be 13 % to meet net-zero emissions by 2050. Repurposing abandoned oil and gas wells (AOGWs) presents a strategic alternative to boost geothermal power by minimising the drilling requirements. This study performed the first cradle-to-grave life cycle assessment to evaluate the environmental performance of three options for geothermal power generation from repurposed oil and gas wells: i) two completely AOGWs (R-GEOdouble); ii) a single completely AOGW (R-GEOsingle); iii) two semi-AOGWs (R-GEOsemi - still in operation but with high water-cut). Their results are then compared with a business-as-usual geothermal power plant (GEObau). All 18 impact categories of the ReCiPe 2016 midpoint methodology plus cumulative energy demand have been analysed in detail, with background data from the Ecoinvent v3.8 database. R-GEOsemi is deemed the most promising repurposed system, exhibiting the lowest values in 11 impact categories. Specifically, R-GEOsemi produces 34 %, 23 %, and 14 % less CO2 eq./kWh when compared to GEObau, R-GEOdouble, and R-GEOsingle, respectively. Conversely, R-GEOdouble performed the worst in 12 impact categories, and the second worst in the rest of the indicators. Meanwhile, GEObau achieved the lowest impacts in nine categories when compared with repurposed systems, indicating the reduction of drilling and construction activities cannot always guarantee the mitigation of all environmental impacts. Sensitivity analyses showed that a longer lifetime could lower environmental impacts, but increasing annual power generation is constrained by site-specific factors. A ‘breakeven’ point analysis revealed that 85 % of repurposed systems' impact indicators could match GEObau if their lifetime reaches 30 years, but this remains uncertain. The findings of this study will be of interest to national and local governments developing future policies aimed at renewable energy transformation from oil and gas industries.
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