Evaluation of Loop Current/Loop Current Eddy Fronts to Guide Offshore Oil & Gas Operations

Abstract

The unique circulation characteristics of the Gulf of Mexico (GOM) pose a significant threat to the safety of offshore oil and gas operations pertaining to installation of new production systems, drilling, and maintenance of existing offshore infrastructure. Operators in the area rely on realistic estimates of the location of the sharp fronts (regions of high horizontal shear) characteristic of the warm-core Loop Current (LC) and Loop Current Eddies (LCEs) and smaller cold core cyclonic eddies (CEs) to estimate working windows. However, locating these features is not a trivial undertaking because it requires review and analysis of multiple observational and model data sources. In this paper, we describe the frontal analysis (FA) methodology used to define such features. This technique has been accepted by industry as the best representation of the continuous front that delineates the most distinct current gradients defining the sharp outside edge of the LC/LCEs. Definition of LC/LCE features is accomplished by defining the position and extent of the associated front, defined as the 1.5 knot current threshold. This involves performing an analysis of satellite imagery (snapshots and composites) and satellite-derived products (altimetry and geostrophic velocities), in-situ measurements (i.e., public and proprietary drifting buoys, rig-mounted ADCPs, vessel-mounted ADCP transects, etc.), and previous feature location/progression analyses, all weighted appropriately. The resulting front is then used to map these features and provide actionable information regarding their surface current velocities, migration speed and direction, angular rotation, and axis orientation. Systematic analysis of the behavior of the LC system since 1984 has resulted in a unique oceanographic dataset comprising the location and evolution of LCEs. By incorporating frequent deployment of aircraft-deployed, satellite-tracked, drogued drifting buoys and the analysis of their track data, the FA provides the most accurate and extensive near-real-time information available regarding the location and intensity of currents affecting offshore operations. WHG’s FA product is commonly accepted throughout the industry and within the scientific community as the closest to ground truth for the placement of the major oceanographic features in the region. Understanding the details of this methodology will provide the basis for comparison of observations with new numerical modeling efforts (under development as part of the NASEM UGOS program) to effectively assess the accuracy of nowcast results and will eventually lead to better model forecasts for the benefit of various stakeholders.