Seafloor subsidence is an observable effect of reservoir compaction, and hence provides important information for the management of offshore reservoirs. In some extreme cases, seafloor subsidence can compromise the safety of the installations and even cause well failure.

This abstract proposes a new, patented system for real-time monitoring of subsidence over large areas with sub-cm accuracy. The system consists of two main elements. The first is a grid of pressure sensors permanently deployed on the seafloor. The sensors can be integrated in a full-scale permanent reservoir monitoring system or a smaller caprock integrity monitoring system.

The second element is a periodical surveying that provides the calibration of the seafloor sensors, by means of the comparison of the real-time seafloor measurements with the subsidence measured between the baseline and the repeat surveys.

This abstract describes first the method used for the periodical surveying, traditionally used for measuring both 4D gravity and subsidence. Then, the challenges related with the integration of pressure sensors in a permanent monitoring system at the seafloor are introduced, and the need for an in-situ correction for the drift of the sensors is motivated. The new method for solving this problem is described in the last section.


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