Ola Eiken¹, I. Brevik¹, R. Arts², E. Lindeberg³, K. Fagervik⁴

(1) Statoil, Trondheim, Norway
(2) NITG-TNO, Trondheim, Norway
(3) SINTEF, Trondheim, Norway
(4) Schlumberger Geco-Prakla, Trondheim, Norway

ABSTRACT: Seismic Monitoring of CO2 Injected into a Marine Acquifer

Since 1996 Statoil has injected about 3 million metric tons of CO2 for disposal into a saline aquifer. Numerical flow modelling suggested that vertical permeability and horizontal shales will control the short-term CO2 migration, while long term (> 25 years) migration may be controlled by the topography of the top seal and the horizontal permeability. Monitoring the behaviour of the CO2 in the sand formation and the sealing capacity of the overlying shale cap rock are key elements in understanding the dynamics of the injection process. We expected that a large contrasts in seismic properties would cause even thin layers containing CO2 to be detected in a time-lapse seismic survey, and a repeated 3D seismic dataset was acquired in 1999, after about 2 million metric tons of CO2 had been injected.

The time-lapse seismic show a large increase in reflectivity within the sand. Strong reflections arise from several (mainly four) vertical levels. These results indicate that CO2 is trapped beneath thin shale layers, the gas has migrated up to 1 km away from the injection point and is filling up a topographic high. Only a small portion has reached the top of the sand, and there are no signs of CO2 above the top seal. A distinguished velocity push-down can be used to estimate the volume of free CO2 gas. The volume is in agreement with estimates based on total injected masses.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado