Subsidence measurement and improved statics solutions through accurate node depth determination during time-lapse deepwater OBN surveys

Principles from gravity-subsidence surveys have been integrated in OBN operations to accurately measure relative node depths using a technology called DepthWatch. In our deep-water fields, the accuracy obtained is <5 cm, much better than that from OBN-reported depths or acoustic bathymetry data. We present a novel workflow to produce a measurement of seabed subsidence with an accuracy of 3 cm, by comparing node depths measured at successive OBN surveys in the same field. Accurate subsidence measurements are important for geomechanical model calibration and for understanding field-scale compressibility. This information can be useful for early identification of challenges to the stability of field infrastructure. We also demonstrate that accurate node depths contribute to improved OBN water statics solutions and reduce noise in high-fidelity 4D seismic data, improving our understanding of the field in production.