Monitoring CO₂ saturation using time‐lapse amplitude versus offset analysis of 3D seismic data from the Ketzin CO₂ storage pilot site, Germany

Abstract

The injection of CO2 at the Ketzin pilot site commenced in June 2008 and was terminated in August 2013 after 67 kT had been injected into a saline formation at a depth of 630–650 m. As part of the site monitoring program, four 3D surface seismic surveys have been acquired to date, one baseline and three repeats, of which two were conducted during the injection period, and one during the post‐injection phase. The surveys have provided the most comprehensive images of the spreading CO2 plume within the reservoir layer. Both petrophysical experiments on core samples from the Ketzin reservoir and spectral decomposition of the 3D time‐lapse seismic data show that the reservoir pore pressure change due to CO2 injection has a rather minor impact on the seismic amplitudes. Therefore, the observed amplitude anomaly is interpreted to be mainly due to CO2 saturation. In this study, amplitude versus offset analysis has been applied to investigate the amplitude versus offset response from the top of the sandstone reservoir during the injection and post‐injection phases, and utilize it to obtain a more quantitative assessment of the CO2 gaseous saturation changes. Based on the amplitude versus offset modelling, a prominent decrease in the intercept values imaged at the top of the reservoir around the injection well is indeed associated solely with the CO2 saturation increase. Any change in the gradient values, which would, in case it was positive, be the only signature induced by the reservoir pressure variations, has not been observed. The amplitude versus offset intercept change is, therefore, entirely ascribed to CO2 saturation and used for its quantitative assessment. The estimated CO2 saturation values around the injection area in the range of 40%–60% are similar to those obtained earlier from pulsed neutron‐gamma logging. The highest values of 80% are found in the second seismic repeat in close vicinity to the injection and observation wells.

Time-lapse applications of the Marchenko method on the Troll field

“…Time-lapse seismic has become increasingly important to monitor fluid flows and geomechanical changes in subsurface reservoirs, such as observing pressure and saturation changes (Johnston et al, 1998;Landrø, 2001;Dadashpour et al, 2007), monitoring CO 2 storage sites (Chadwick et al, 2010;Pevzner et al, 2011;Ivandic et al, 2018) and assessing compaction and subsidence (Barkved and Kristiansen, 2005;Hatchell and Bourne, 2005). Typically, these studies compare an initial baseline study followed by one or more monitor studies.…”

Time‐lapse applications of the Marchenko method on the Troll field

“…Time‐lapse seismic has become increasingly important to monitor fluid flows and geomechanical changes in subsurface reservoirs, such as observing pressure and saturation changes (Dadashpour et al., 2007; Johnston et al., 1998; Landrø, 2001), monitoring CO 2 storage sites (Chadwick et al., 2010; Ivandic et al., 2018; Pevzner et al., 2011) and assessing compaction and subsidence (Barkved & Kristiansen, 2005; Hatchell & Bourne, 2005). Typically, these studies compare an initial baseline study followed by one or more monitor studies.…”

Monitoring CO2 Injection at the CaMI Field Research Station Using Microseismic Noise Sources

“…Carbon capture, utilization and storage encompasses technologies to capture carbon dioxide (CO 2 ) from the atmosphere or from industrial emission sites, and to subsequent recycle the captured CO 2 for exploring or determining safe and permanent storage options (Pacala & Socolow, 2004). A relatively mature option is injecting nearly pure CO 2 streams into geologic formations for long‐term storage (Pires et al., 2011) which has demonstrated its effectiveness in a range of injection projects worldwide, including the Cranfield oilfield in the United States (Hovorka et al., 2013), the Jilin Oilfield in China (Ren et al., 2016), the Sleipner field offshore Norway (Chadwick & Noy, 2015), the Ketzin pilot site in Germany (Ivandic et al., 2018), the In Salah field in Algeria (White et al., 2014), potential sites in Korea (Kim, 2013), and the Aquistore in Saskatchewan, Canada (Emberley et al., 2004; Stork, Nixon, et al., 2018). Timely detection of subsurface structural changes resulting from stresses triggered by CO 2 injection is critical to prevent or mitigate potential containment failures and to demonstrate the security of the CO 2 within the storage complex (Gholami et al., 2021).…”