Synthetic versus real time‐lapse seismic data at the Sleipner CO2 injection site

Abstract

CO2 has been injected into the Utsira Sand at Sleipner since 1996, with more than 9 million tonnes currently in the reservoir. Seismic monitoring surveys to follow the migration of the CO2 in the reservoir have been carried out in 1999, 2001, 2002, 2004 and 2006. The CO2 plume is imaged on the seismic data as a prominent multi‐tier feature, comprising a number of bright sub‐horizontal reflections, growing with time, interpreted as arising from up to nine discrete layers of high saturation CO2, each up to a few metres thick. Quantitative seismic interpretation of the time‐lapse data has included synthetic seismic modelling to derive CO2 distributions in the reservoir. Convolution‐based modelling has shown that seismic reflection amplitudes are broadly related to layer thickness via a tuning relationship. However acquisition geometry, lateral velocity changes, mode conversions and intrinsic attenuation are all likely to affect amplitudes and need to be incorporated for a rigorous quantitative analysis. A first attempt to incorporate some of these effects, through more realistic pre‐stack elastic modelling and processing, is presented here. Both the acquisition geometry and the processing sequence of the synthetic data are comparable to the real field data. Results support the basic amplitude‐thickness relationship.