Stratigraphic inversion for CO2 monitoring purposes: a case study for the saline aquifer of Sleipner field

For years, theoretical advances and algorithm improvements in stratigraphic inversion of seismic data have been carried out in the petroleum industry for better reservoir characterization and enhanced oil recovery. Nowadays, these techniques may also be used to evaluate the expansion of a CO2 plume in an underground reservoir. A series of 3D seismic surveys were recorded from 1994 onwards to monitor the injection of CO2 in the Utsira Sand saline aquifer located above the Sleipner East gas field in the Norwegian North Sea. Seismic imaging performed from the vintages acquired in 1999, 2001, 2004, 2006 and 2008 has been shown to be successful in mapping the spread of CO2 over the past decade. The aim of this work is to quantitatively estimate the P-wave impedances via a model-based stratigraphic inversion. We have focused our study on two vintages: the 1994 seismic dataset before CO2 injection, and the 2006 seismic dataset which is the most recent vintage available to us. In spite of some difficulties due to the lack of well log data on the interest area, the full application of our inversion workflow allowed us to obtain 3D impedance cubes including the Utsira Sand.