Lidar and Wave Radar Observations Analysis for Offshore Hurricane Conditions in the Gulf of Mexico

Abstract

Accurate measurement of the vertical profile of wind offshore has become increasingly important in planning, design, and operations, from existing offshore oil and gas to support for the nascent wind energy industry. Using remote sensing, with laser Doppler anemometer (Lidar) systems, has obviated the need for expensive offshore tower construction historically needed to measure the vertical wind profile, and reduced the uncertainties introduced by traditional single point anemometers, which can often suffer from bad positioning (obstruction) and lack of calibration. Similarly, accurate characterization of the wave environment for offshore facilities is an integral part of planning, design and operations. Remote sensing with new wave radar systems allows remote wave field observation, reducing data contamination associated with traditional upward/horizontal-looking acoustic meters, as well as complications in wave buoy deployment. Shell Exploration & Production Co. has recently included both laser anemometer (Lidar) wind profilers and microwave wave radars on several oil and gas platforms in the Gulf of Mexico to better understand the met ocean conditions in and around these structures. To date more than a year’s worth of data has been collected with the combined system collected at tension leg platform (TLP) Ursa, observing a full range of meteorological and oceanographic conditions, representative of the region, including the passage of a hurricane (Nate, Saturday 07 October of 2017), for the first time. This study evaluated the wind profile through the first 100- meters, simultaneously with wave radar measurements from the deck mounted system. The hurricane’s effect on conditions in the Gulf, and the ability of the measurement systems to successfully capture extreme conditions were examined. Despite some interruptions in the wind and wave time series data the signal continued throughout the storm and provided sufficient data to examine. The wind data recorded sustained wind speeds of 35 m/s and maximum speeds up to 40 m/s (90 mph), consistent with NOAA observations at the peak of the storm. Wave data analysis successfully resolved spatially and temporally coherent wave systems that are consistent with expected hurricane conditions, showing a 10 m significant wave height and a maximum wave height of 15 m. Variability in the wind and shear vertical profiles, wave system response, and correlation between the observed wind and wave signals, were evaluated and the observations showed that a transition from wind sea to swell occurred as the storm peak passes. The data also showed the presence of orthogonal wind sea and swell wave systems after the storm peak.