Item

Abstract

The observed CO2 plume behaviour is derived from geophysical and/or geochemical monitoring. The method of 4D seismic observations has proven to provide the most comprehensive image of a CO2 plume in various projects such as Sleipner, Weyburn, or Ketzin. The simulated plume behaviour is derived from reservoir simulation with a model calibrated using monitoring results. Plume observations using any monitoring method are always affected by limited resolution and detection ability. In turn, reservoir simulations will only be able to provide an approximated representation of the occurring reservoir processes. Full conformity between observed and simulated plume behavior is difficult to achieve, if it is at all. Therefore it is of crucial importance for each storage site to understand to what degree conformity can be achieved under realistic conditions, comprising noise affected monitoring data and reservoir models based on geological uncertainties. We applied performance criteria such as plume footprint area, lateral migration distance, plume volume, and similarity index for a comparison between monitoring results (4D seismic measurements) and reservoir simulations, considering a range of seismic amplitude values as noise threshold and a range of minimum thickness of the simulated CO2 plume. This allows assessing the quality of conformance between simulated and observed behavior of a CO2 plume. The Ketzin pilot site is provided with a comprehensive monitoring data set and a history-matched reservoir model. Considering the relatively high noise level, which is inherent for land geophysical monitoring data, a reasonable conformance between the observed and simulated plume behaviour is demonstrated at Ketzin. However, it is also shown that maximum conformance which can be achieved between monitoring data and simulations is affected by limited resolution related to the small quantities of stored CO2.