Integration of wellbore pressure measurement and groundwater quality monitoring to enhance detectability of brine and CO2 leakage

• Published in: International journal of greenhouse gas control 2019-06, Vol.85, p.143-155
• Main Authors: Yang, Ya-Mei, Dilmore, Robert M., Mansoor, Kayyum, Buscheck, Thomas A., Bromhal, Grant S.
• Format: Article
• Language: English
• Subjects: Bayesian network; Geologic carbon storage; Groundwater; Monitoring detectability; Risk management; Wellbore leakage
• ISSN: 1750-5836; 1878-0148
• DOI: 10.1016/j.ijggc.2019.04.004

•An approach integrating wellbore monitoring and risk reduction options is proposed.•CO2 leakage is more easily detected at shallower depths due to CO2 buoyancy.•Alkalinity can help distinguish CO2 leakage from other contamination sources.•Pressure monitoring is a valuable indicator of leakage events at early stages.•An example Bayesian network is built for evaluating the risk reduction options. Leakage detectability is a key consideration in evaluating the effectiveness of a measurement, monitoring and verification (MMV) plan for a geologic carbon storage (GCS) project. While studies have shown that surface-based, geophysical monitoring methods may be sensitive enough to detect CO2 leakage, these methods are an indirect indicator of leakage. A drawback to relying on direct geochemical monitoring is that by the time a significant leak is confirmed, it may be too late to mitigate or remediate the environmental impacts. In this study, we combine information from geophysical and geochemical monitoring methods to provide an integrated diagnosis of leakage events. The detectability for various monitoring parameters (pH, TDS, alkalinity, Ca, Cl, Na, and pressure) collected from monitoring wells are evaluated by leakage detection probability, using simulated wellbore-leakage/plume-migration events and monitoring scenarios for a hypothetical GCS operation at the Kimberlina site in California, USA. The NUFT code is used to model these events, by coupling wellbore-leakage simulations to 3-dimensional reactive, multi-phase, flow and transport simulations of brine and CO2 leakage-plume migration in aquifers overlying the GCS reservoir. Wellbore leakage in legacy wells located 1.4, 3.4 and 6.8 km from the CO2 injector is evaluated for a range of (1) wellbore bottom-hole pressure and CO2 saturation determined by GCS simulations, (2) regional groundwater gradient in the aquifers, and (3) wellbore permeability. Simulated leakage-induced changes in seven monitoring parameters at different depths are used to calculate the corresponding detection probabilities, based on the background distribution data and selected monitoring-technology detection thresholds. The responses for these monitoring parameters are tested and combined to enhance the overall detectability. The results indicate the leakage signals are more easily detected at shallower depths where buoyant CO2 has migrated and flashed from supercritical to gas phase, causing a large increase in CO2 volume. While the re