Integrated Study of a Complex Seabed For the Stones FPSO

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Abstract
Shell's Stones field is located below the Sigsbee escarpment on the continental rise in the Walker Ridge area of the Gulf of Mexico, in a water depth of approximately 9,500-ft. The seafloor is irregular due to the presence of furrows, which have been eroded by bottom currents. These features, combined with positioning uncertainties associated with surveys in this extreme water depth, posed a unique challenge to characterization of the seabed and to siting of infrastructure. Design soil properties were selected by integrating Autonomous Underwater Vehicle survey data with data from two geotechnical investigations. These data sets are typically correlated by using the seafloor as the vertical reference datum. This was not possible in the Stones field, so the data was instead correlated to a marker horizon, which was common to both the shallow seismic and the geotechnical data sets. Additionally, seafloor bathymetry data were screened using pre-determined criteria to optimize FPSO mooring anchor locations. This paper presents sample geophysical and geotechnical data from the Stones field and describes the process used to integrate the data and develop design information. The selection of FPSO mooring anchor locations within the variable bathymetry is also described. Finally, installation records from the FPSO mooring system are presented, which demonstrate the value of the integrated approach to site characterization. The process for data integration at Stones can serve as a model for future developments, with complex seafloors.