(OTC 23950)AUV3Dm: Detailed Characterization of Shallow Soil Strata and Geohazards Using AUV Subbottom Profiler 3-D Micro Volumes

摘要

This paper describes the acquisition, processing, and application of deepwater subbottom profiler data acquired using an AUV survey vehicle and processed as a micro 3-D seismic data volume (AUV3Dm data). AUV3Dm data precisely defines foundation-zone conditions in 3-D space without gaps. The AUV3Dm methodology consists of doing a very detailed 3-D seismic survey (4-m line spacing) over a very small area (for example, 390 x 500 meters) using a high-frequency seismic (sub-bottom profiler, SBP) source (typ. 2 kHz to 12 kHz). The resulting 3-D data volume has a bin spacing of 4 x 0.5 meter, provides near-core-scale vertical resolution to a maximum of 75 to 100 m or so below seafloor, and allows the robust dataanalysis functionality inherent in 3-D seismic volumes (arbitrary lines, attribute extractions, time and horizon slices, horizon flattening, etc.). This methodology is being used where a very detailed 3-dimensional characterization of shallow soil strata and geologic features (such as thin, discontinuous sandy zones; fault planes; fluid vents; gassy zones, etc.) is required to help optimize deepwater production structure siting and foundation design. One specific application is providing detailed characterization of proposed anchor-pile sites so that faults and other potential hazards can be avoided when installing the anchors. Further, the ~20-cm vertical resolution of the SBP data facilitates detailed correlation with sediment cores and cone-penetrometer data, thus allowing “calibration” of the micro 3-D volume with geotechnical properties, and enhancing its use as a tool to predict soil conditions away from geotechnical stations. Use of the AUV3Dm methodology should be considered whenever shallow foundations are required in areas of complex stratigraphy or local geologic hazards.