Statistical performance of CO₂ leakage detection using seismic travel time measurements

Abstract

Monitoring for possible CO2 leakage is an important part of a safe and effective geological sequestration program. Seismic monitoring has been implemented in several pilot sequestration sites for site characterization and CO2 leakage detection. This study evaluates the detection power of seismic wave travel time measurements and statistical tests at different CO2 leakage rate levels. A simplified rock physics model is assumed for monitoring zones at sequestration sites and the effects of leakage‐induced changes in pressure and CO2 saturation on P‐wave travel times are modeled. The empirical distributions of detection power using the P‐wave travel time for four regions in the permeability‐porosity input space at four leakage levels are obtained from the Monte Carlo uncertainty analysis with a stochastic response surface method. The detection power using the P‐wave travel time measurements and test alone is generally not high enough, unless the porosity and the permeability of the monitoring zone are high, and/or a long period of time has elapsed since the leakage occurred. For monitoring layers with lower permeability and porosity, measurements from other monitoring techniques will likely be needed to increase the probability that leakage events are detected and addressed in a timely manner. © 2015 Society of Chemical Industry and John Wiley & Sons, Ltd

Modeling changes in pressure due to migration of fluids into the Above Zone Monitoring Interval of a geologic carbon storage site

“…Ideally, these deep monitoring techniques will have the capability to identify and resolve the onset, location, and volume of leakage from the reservoir in a systematic and timely manner. The monitoring of pressure changes, as an indication of leakage, represents one such approach (Sun et al, 2012;Jung et al, 2013;Azzolina et al, 2014;Wang and Small;2015). Recent studies (Nicot et al, 2009;Hovorka et al, 2013) show the potential utility of monitoring to detect and estimate leakage and pressure changes above the caprock.…”