Integration of 3D seismic with satellite imagery at in salah CO 2 sequestration project, Algeria

Abstract

The Krechba field is located in the Algerian central Sahara desert, and was developed in July 2004 as part of a joint venture with BP, Sonatrach and Statoil. The natural gas in the fields contains up to 10% , which has to be reduced to 0.3% before sale, resulting in the production of around 1 million tonnes/year . The is re‐injected into the water leg of the Krechba Carboniferous Sandstone gas producing reservoir (20 m thick) at a depth of 1,900 metres. An exploration 3D seismic survey was acquired in 1997 but this was designed to image prospects in the Carboniferous and Devonian sequences rather than the overburden where quality is low. However, for sequestration monitoring the structure and characteristics of the overlying section are important for understanding and modelling of long‐term behaviour. Further seismic survey(s) are planned for overburden imaging and 4D time lapse evaluation of movement and long term sequestration in the subsurface. Time lapse satellite images (InSAR) collected since start of injection show clear ground elevation of up to 8mm/year around the three injectors while subsidence is apparent in the area of maximum gas production. The images have also confirmed the is moving in the direction of preferred fracture orientation at reservoir level. Integration of the 3D seismic with the satellite images, when combined with other measurements such as wellhead samples, is proving to be a powerful tool in tracking the subsurface migration of at Krechba.