Pilot sites storing small amounts of carbon dioxide in a variety of geological settings are an important component for the industrial and governmental stakeholders in order to gain operational experience in storage and in the monitoring at various scales. An important aspect is also to gain confidence in the ability of monitoring technologies to pay a significant contribution to the safe operation of larger scale demonstration and industry scale sites, especially in the perspective of the wider public.
The Ketzin Pilot Site for CO2 Storage has entered its post-closure phase after injection was terminated in the end of August 2013. For approximately 5 years, 67,271 metric tons of CO2 have been injected into a saline aquifer reservoir at 630 – 650 m depth. At the pilot site, various monitoring technologies were applied, including pulsed neutron gamma logging (PNG), electrical resistivity tomography (ERT) and borehole as well as surface seismic measurements. The integrated monitoring approach allowed to combine results of borehole logging, lab experiments and surface measurements in order to quantitatively estimate the proportion of stored CO2 in the reservoir which has actually been imaged in the geophysical anomalies.
During the injection phase of the pilot site, two repeat surveys of 3D time-lapse seismics were acquired. The repeat surveys were performed approximately one year and three years after injection started, respectively. Both surveys were able to detect a time-lapse amplitude anomaly characterized by strong lateral heterogeneity which can be interpreted as an indication of the reservoir's heterogeneity caused by the complex sedimentary history in a fluvial environment. The quantitative estimations indicate that approximately 90 – 95% of the CO2 injected were imaged by the surface seismic surveys, leaving the remaining proportion residing in a very thin layer (less than ∼:5 m) undetected by the measurements.