Abstract
Potential leakage of reservoir fluids is considered a key risk factor for geologic CO2 sequestration (GCS), with concerns of their chemical impacts on the quality of overlying underground sources of drinking water (USDWs). Effective risk assessment provides useful information to guide GCS activities for protecting USDWs. In this study, we present a quantified risk assessment case study of an active commercial-scale CO2-enhanced oil recovery (CO2-EOR) and sequestration field, the Farnsworth Unit (FWU). Specific objectives of this study include: (1) to quantify potential risks of CO2 and brine leakage to the overlying USDW quality with response surface methodology (RSM); and (2) to identify water chemistry indicators for early detection criteria. Results suggest that trace metals (e.g., arsenic and selenium) are less likely to become a risk due to their adsorption onto clay minerals; no-impact thresholds based on site monitoring data could be a preferable reference for early groundwater quality evaluation; and pH is suggested as an indicator for early detection of a leakage. This study may provide quantitative insight for monitoring strategies on GCS sites to enhance the safety of long-term CO2 sequestration.
Highlights
Carbon dioxide capture and sequestration (CCS) in geologic formations is considered a promising approach for mitigating CO2 emissions, by injecting CO2 from stationary sources into deep geologic formations [1,2]
With the trained polynomial response surface methodology (RSM) equations, selected parameters were calculated with 10,000 random cases
Cumulative distribution functions (CDF) were obtained and they were used for forecasting the likelihood that the leakage would impact groundwater quality over 200 years
Summary
Carbon dioxide capture and sequestration (CCS) in geologic formations is considered a promising approach for mitigating CO2 emissions, by injecting CO2 from stationary sources into deep geologic formations [1,2]. It is believed that the risks of geologic CO2 sequestration (GCS) to the environment and human health are minimized with monitoring and managements of the sites, especially for operational reservoirs with pressure managements [6,7,8]. The concern of reservoir fluids, especially CO2 leakage to overlying underground sources of drinking water (USDWs) cannot be completely ruled out [9,10,11,12]. Carbon dioxide itself is not hazardous to groundwater quality, but it triggers pH reduction, water-sediment interactions, and potential toxic trace metal release from sediments [13,14,15].
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