Improving seismic processing and measuring seabed subsidence through accurate node depths

In deepwater OBN, uncertainties in sensor positions lead to errors in the static solutions and deteriorate imaging capabilities. In particular, node depths are generally measured with an accuracy of a few meters. Corrections can be applied, but they are complicated by changes in tides and water velocities that couple with positioning errors.The patented DepthWatch technology has been used for decades to monitor the vertical deformation of the seafloor over hydrocarbon-producing fields with an accuracy of a few millimeters. The technology has recently been incorporated into OBN surveys, providing an accuracy of a few centimeters in node depths in deep waters.These new accurate node depths are used in seismic data processing to update the statics solutions. With accurate node depths, timing error corrections are fully decoupled from the bathymetry errors.In 4D applications, the subtraction of accurate node depths at the baseline and repeat surveys provides a measurement of seabed subsidence in the area covered by the node grid. This information is useful for updating and calibrating geomechanical and reservoir models.