Acquisition Using Autonomous Marine Vehicles: Wave Glider Field Test, Offshore Abu Dhabi

Abstract

Abstract A field test was conducted utilizing autonomous marine vehicles (AMVs) and 3D sensor arrays (3DSAs) to record and compare seismic data generated during an ocean-bottom cable (OBC) survey. The test was a field verification to check that the AMV platform and the sensor array can deliver high-quality seismic data in a form that can be successfully processed and compared to ocean-bottom fixed-receiver data. Three AMVs, each towing a 3D sensor array, were deployed during the acquisition of an OBC 3D survey in shallow water, offshore Abu Dhabi. The test was conducted to (a) assess the feasibility of seismic acquisition using AMVs and 3D sensor arrays including safe deployment and retrieval, (b) evaluate the performance of the 3D sensor arrays based on holding station capability, maintenance of desired depth, and accuracy of measurements of pitch and orientation, and (c) compare the quality of the acquired seismic data with the pressure data recorded in the OBC survey. The water depths across the acquired survey area average approximately 20 m. Due to the very shallow water depths, towed-streamer acquisition is seldom used offshore Abu Dhabi, limiting the marine seismic acquisition methods to either OBC or ocean-bottom nodes (OBN). The AMV and 3D sensor array are ideally suited to operate and record seismic data in this shallow-water environment, providing a potentially viable alternative for off-bottom recording or as a method to supplement OBC or OBN data acquisition. The feasibility test conducted in offshore Abu Dhabi demonstrated the successful and safe deployment, seismic data acquisition, and retrieval of the AMV and 3D sensor array. The evaluation criteria indicate the consistent performance of the AMV and 3D sensor array, and that the recorded data are comparable to the OBC component data in terms of signal-to-noise ratio and frequency bandwidth. The processing flow that may typically be applied on the OBC data for signal processing, velocity model building, and imaging may also be applied to the 3D sensor array data. Marine seismic data can be acquired using towed-streamer arrays, ocean-bottom cables, or nodes in which the receivers are placed in fixed positions on the seafloor. Limitations to acquisition in each case may be determined by water depth and seafloor topography, or operational constraints due to in-situ infrastructure and obstructions. In the cases where these sorts of limitations arise, a loss in operational efficiency may easily result, which will ultimately drive the acquisition cost up, or may even result in poor or no data coverage. Using the AMV offers the potential to acquire seismic data in these cases where adverse existing factors may hamper standard acquisition methods.