Measurement and Modeling of Topographically Trapped Waves Along the Sigsbee Escarpment

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper OTC 20694, ’Measurements and Modeling of Topographically Trapped Waves Along the Sigsbee Escarpment,’ by Steven L. Morey and Dmitry S. Dukhovskoy, Florida State University, and Cortis Cooper, Chevron Energy Technology Company, originally prepared for the 2010 Offshore Technology Conference, Houston, 3-6 May. The paper has not been peer reviewed. Observations of strong currents with wave-like behavior have been documented from specific sites near the seafloor along the Sigsbee escarpment (SE) in the northern Gulf of Mexico (GOM). These currents tend to occur when the Loop Current (LC) or its separated eddies are in the vicinity, typically to the east of the SE. Observational and numerical-modeling efforts were funded in 2008 to understand these events and their dynamics better. The full-length paper summarizes the observations, numerical-model hind-casts, and process studies. Introduction The SE runs through the Walker Ridge and Atwater Valley blocks where many new discoveries are being made and developed [e.g., Jack/St. Malo, Big Foot (BF), and Atlantis]. While these cover a relatively small number of blocks, pipe-lines of blocks developed farther south can be affected by flow dynamics along the SE. Strong near-bottom currents, with instantaneous speeds exceeding 100 cm/s, have been observed along the SE. Such strong currents can cause costly delays in drilling and present major engineering challenges to the design of production risers and pipelines. Despite their importance, only a few strong (greater than 50 cm/s) events have been measured to date, and no well-validated numerical model has been developed. To help fill this gap, DeepStar (DS) funded two efforts in 2008—deployment off four moorings for 1 year along the SE and development of a numerical model. In addition to the DS measurements, Fig. 1 shows the bathymetry of the GOM-model domain (left) with detail of the SE-model domain (right). Locations of the Minerals Management Service I2 and I1 moorings, the DS moorings, and the BF site are shown on the right. Observations along the upper portion of the SE beginning in September 1999 showed strong currents with fluctuations resembling those associated with topographic Rossby waves (TRWs), near the 2000-m bottom, with speeds estimated from the low-pass filtered time series at greater than 85 cm/s. It is interesting that each of the documented strong events occurred when a strong LC eddy (LCE) or meander of the LC was in the vicinity, particularly with the SE near its western edge. During the early months of 2009, the LC had extended far to the northwest and formed the Eddy Darwin. Several events of moderately strong currents were observed near the bottom during this time.