4D/4C Practical Interpretation at the Valhall Field: Dealing with Technology Change, Seismic Imaging Challenge, and Complex Subsurface on a Mature Field

The Valhall chalk field has been a pioneer for seismic technologies. This giant oil field, on production since 1982, has subsequently seen its subsurface revealed by 2D seismic in the 70's, first streamer 3D seismic in 1992, 3D OBS imaging with both PP and PS events in 1997, then 4D seismic with ultimately the installation of a permanent array on the seafloor in 2003. With 19 ocean-bottom surveys acquired since 2003, the subsurface team has a very dense imaging of the field activity, hence the name Life Of Field Seismic. Global economic constraints have also been influential in the strategy for the field development, but with the constant concern of maintaining safety and quality. Recent years have indeed seen the transition from the use of the permanent array to nodes acquisition. Beyond this technical geophysical challenge, the present paper will focus on the use of the latest 4D/4C seismic, the full field strategy, and highlight some practical challenges linked to the nature of the seismic data (time-variance and data size).