The Evolution of 4D Monitoring at the Valhall Field, from Permanent Cables to Retrievable Nodes

The first large scale permanent reservoir monitoring system was installed at the Valhall field in 2003. Ocean bottom cables were trenched beneath the seabed, in order to provide frequent time-lapse images of the reservoir. Changing requirements for acquisition frequency and areal coverage have led to the utilization of retrievable ocean bottom nodes for the most recent surveys.

An overlap in the transition from permanent to retrievable instruments provided an opportunity to make a direct comparison of the 4D signal recorded simultaneously by both cables and nodes. We compare the 4D quality of both systems using standard repeatability metrics, and demonstrate that ocean bottom nodes provide high quality time-lapse images that complement the historical 4D library of data from the permanent array.