Accurate Measurement of Seabed Subsidence at the Ormen Lange Field


Field-wide seafloor subsidence measurements are a mature reservoir monitoring technology, utilized in ten hydrocarbon fields in Norway. These measurements provide lateral information on pore compaction and pressure depletion in the reservoir. The survey method uses water pressure measurements at the seafloor as a starting point and reaches accuracies of 2 – 5 mm. Field cases demonstrate that the lateral distribution of subsidence can be used to identify undrained compartments and to calibrate the geomechanical model, hence providing improved interpretation of seismic time-shifts in the overburden.

Shell manages the Ormen Lange field by utilizing a combination of technologies: time-lapse gravity is used to quantify mass changes in the reservoir, providing valuable constraints for dynamic reservoir modelling; seabed subsidence is used as an indirect measurement of compaction throughout the reservoir; and 4D seismic provides the vertical resolution required to interpret these datasets in three dimensions.

In this abstract we present a solution, based on temperature-stabilization, that eliminates temperature-induced effects in subsidence surveys. We show that it provides sub-centimeter accuracy at the Ormen Lange field, with a range of depths extending for almost one kilometer. Finally, we discuss how this data is used and combined with other data types to manage the reservoir.

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