Water Velocity and Tide Measurement in Marine Seismic Acquisition

Uncertainties in water velocity and tidal variations make significant contributions to the non-repeatability of marine time-lapse seismic data, and affect the quality of 4D data processing and interpretation. To reduce such uncertainties, we developed a seafloor device called Pressure Inverted Echo Sounder (PIES) that provides direct measurements of water velocity and tides during seismic data acquisition. Placing PIES units at multiple locations allows determination of lateral and vertical water velocity profiles. We carried out a series of field trials of PIES in the deepwater Gulf of Mexico. Processing and analysis of the field trial data yields precise measurements of average water velocities and tide height variations that are consistent with remotely operated vehicle (ROV) temperature-pressure-conductivity measurements and oceanographic data from nearby stations. A recent field trial conducted during a 4-month Ocean Bottom Nodes (OBN) survey completed in January 2012 is discussed in details.