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Hydrobiochemical controls and limitations on CO2 storage in enhanced oil recovery reservoirs and on the occurrence of methanogenic crude oil biodegradation
Shelton, Jenna L.
Shelton, Jenna L.
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2016
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2016-11-12
Abstract
With impacts of climate change apparent worldwide, low carbon dioxide (CO2) emitting forms of hydrocarbon extraction could decrease CO2 emissions to the atmosphere while also continuing to provide reliable energy sources to our fossil fuel-dependent society. This research looks to better understand two different ways of enhancing hydrocarbon (i.e., both crude oil and natural gas) production in oil reservoirs: miscible CO2 enhanced oil recovery (EOR) coupled with permanent CO2 storage, and methane production via methanogenic crude oil biodegradation, which converts crude oil in-situ into a cleaner-burning fuel, natural gas. Noble gas and isotopic tracers were used to track the fate of CO2 injected into three different project phases of a miscible CO2 EOR site. The current volumes of retained CO2 ranged from 39-61% of the total injected gas volume, while no major changes in noble gas isotopic composition were detected between injected and produced gases, suggesting no active CO2 dissolution dissolution. However, a reasonable assumption of 40% inaccessible pore space suggests effective storage of the retained CO2. Formation fluids and biomass from a methanogenic, biodegraded oil reservoir in Louisiana, USA, were collected to better understand how environmental parameters (e.g., salinity, temperature) may impact methanogenic crude oil biodegradation and reservoir microbiology. Overall, crude oil biodegradation and methanogenesis were not coupled across this basin; the greatest amount of crude oil biodegradation occurs in wells with the least extent of methanogenesis. However, methanogenic archaea dominate the microbial structure of every well, regardless of the observed extent of methanogenesis. Significant differences in microbial community structure were observed between samples grouped by chloride concentration, location within the basin, and amount of biodegradation. The low salinity, highly biodegraded wells had a particularly distinct microbial structure, indicating that salinity may be a major driver of microbial community composition and metabolism in this reservoir. Overall, these results suggest that low salinity reservoirs with moderately biodegraded crude oil and an abundance of methanogens may be ideal candidates for stimulating methanogenic crude oil biodegradation.
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