Gulf of Mexico low-frequency ocean soundscape impacted by airguns

An accurate prediction of the global response of a floating production and storage offloading (FPSO) system under harsh environmental conditions is of great importance in order to achieve the reliability and safety operation of the whole system. FPSOs may be subjected to significant resonant oscillations in the horizontal plane due to low frequency (LF) wave effects and wind excitation forces. These characteristics may contribute to the increase in surge due to the low level of viscous hull damping. Additionally, it has been observed that when the water depth increases, the coupled effects (damping, inertia and restoring force) contributions from mooring lines and risers increases. This paper investigates the LF response behavior of a deepwater FPSO unit in the Gulf of Mexico by carrying out a coupled analysis based on a nonlinear time domain analysis. A 3D model based on boundary integrated element method is used to investigate the hydrodynamic behaviour of the floater as well as a 3D finite element model for each of the slender elements representing the mooring lines and risers. The LF motions of a FPSO with a typical arrangement of catenary mooring lines and steel catenary risers is studied for surge, sway and yaw mainly. The hydrodynamic characteristics of the FPSO are studied through both Newman’s approach and the full Quadratic transfer function. The coupling effect of the floater and mooring/riser systems is examined by comparing the tensions in mooring lines/risers and the global responses of the system in six degree of freedom. The nonlinearity of the hydrodynamics of wave-vessel interaction and the dynamic contribution of mooring lines and risers are investigated with storm and hurricane events for a particular location in deep water Gulf of Mexico (GOM).

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The Wolfspar experience with low-frequency seismic source field data: Motivation, processing, and implications

The Leading Edge ◽

10.1190/tle41010010.1 ◽

2022 ◽

Vol 41 (1) ◽

pp. 9-18

Author(s):

Andrew Brenders ◽

Joe Dellinger ◽

Imtiaz Ahmed ◽

Esteban Díaz ◽

Mariana Gherasim ◽

...

Keyword(s):

Gulf Of Mexico ◽

Seismic Data ◽

Field Data ◽

Model Building ◽

Low Frequency ◽

Seismic Source ◽

Velocity Model ◽

Seismic Sources ◽

Velocity Model Building ◽

Air Gun

The promise of fully automatic full-waveform inversion (FWI) — a (seismic) data-driven velocity model building process — has proven elusive in complex geologic settings, with impactful examples using field data unavailable until recently. In 2015, success with FWI at the Atlantis Field in the U.S. Gulf of Mexico demonstrated that semiautomatic velocity model building is possible, but it also raised the question of what more might be possible if seismic data tailor-made for FWI were available (e.g., with increased source-receiver offsets and bespoke low-frequency seismic sources). Motivated by the initial value case for FWI in settings such as the Gulf of Mexico, beginning in 2007 and continuing into 2021 BP designed, built, and field tested Wolfspar, an ultralow-frequency seismic source designed to produce seismic data tailor-made for FWI. A 3D field trial of Wolfspar was conducted over the Mad Dog Field in the Gulf of Mexico in 2017–2018. Low-frequency source (LFS) data were shot on a sparse grid (280 m inline, 2 to 4 km crossline) and recorded into ocean-bottom nodes simultaneously with air gun sources shooting on a conventional dense grid (50 m inline, 50 m crossline). Using the LFS data with FWI to improve the velocity model for imaging produced only incremental uplift in the subsalt image of the reservoir, albeit with image improvements at depths greater than 25,000 ft (approximately 7620 m). To better understand this, reprocessing and further analyses were conducted. We found that (1) the LFS achieved its design signal-to-noise ratio (S/N) goals over its frequency range; (2) the wave-extrapolation and imaging operators built into FWI and migration are very effective at suppressing low-frequency noise, so that densely sampled air gun data with a low S/N can still produce useable model updates with low frequencies; and (3) data density becomes less important at wider offsets. These results may have significant implications for future acquisition designs with low-frequency seismic sources going forward.

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Low-frequency current variability observed at the shelfbreak in the northeastern Gulf of Mexico: May–October, 2004

Continental Shelf Research ◽

10.1016/j.csr.2006.08.002 ◽

2006 ◽

Vol 26 (20) ◽

pp. 2559-2582 ◽

Cited By ~ 21

Author(s):

W.J. Teague ◽

E. Jarosz ◽

M.R. Carnes ◽

D.A. Mitchell ◽

P.J. Hogan

Keyword(s):

Gulf Of Mexico ◽

Low Frequency ◽

Northeastern Gulf Of Mexico ◽

Frequency Current

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Low-frequency current variability observed at the shelfbreak in the northeastern Gulf of Mexico: November 2004–May 2005

Continental Shelf Research ◽

10.1016/j.csr.2007.10.005 ◽

2008 ◽

Vol 28 (3) ◽

pp. 399-423 ◽

Cited By ~ 16

Author(s):

M.R. Carnes ◽

W.J. Teague ◽

E. Jarosz

Keyword(s):

Gulf Of Mexico ◽

Low Frequency ◽

Northeastern Gulf Of Mexico ◽

Frequency Current

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Energetics and Kinematics of Inertial Oscillations in the Central Northern GOM

10.4043/31020-ms ◽

2021 ◽

Author(s):

Leonid Ivanov ◽

Rafael Ramos ◽

Drew Gustafson

Keyword(s):

Gulf Of Mexico ◽

Water Column ◽

Low Frequency ◽

Mode Shapes ◽

Loop Current ◽

Inertial Waves ◽

Energy Propagation ◽

Inertial Oscillations ◽

Wide Range ◽

Inertial Currents

Abstract Understanding the physics of generation, propagation, and dissipation of inertial currents is important from a variety of aspects. For the Gulf of Mexico, one such aspect is that these oscillations represent an uncertainty in the measurements and forecasting of the longer-period currents, such as those due to the Loop Current (LC) and meso-scale eddies. The Industry has a practice of applying an ‘uplift’ to estimates of current velocity to account for the effect of tidal and inertial currents in cases when observations or model estimates do not resolve the high-frequency current variability. The value of the ‘uplift’ is assumed to be proportional to the intensity of the low-frequency flow. Our analysis aims at testing whether this assumption is valid by providing a detailed description of the space-time variability, including seasonal changes, of inertial oscillations in the central northern Gulf of Mexico. From the analysis of long-term current profile observations and drifter data we found that, on average, near-inertial oscillations have higher amplitudes outside of the areas of strong low-frequency currents associated with a Loop Current Eddy (LCE). Within the upper 200m of the water column, periods characterized by the downward energy propagation dominate. In the layer below 200m, near-inertial waves propagate upward and downward, and the wave trains cannot be traced to a single source of energy. This suggests near-inertial waves within the main part of the water column are of ‘global’ rather than of ‘local’ origin. For most near-inertial wave generation events through wind forcing, the downward energy propagation could not be traced for any extended period of time and no deeper than approximately 200-m depth. The rate of downward energy propagation in the upper pycnocline is on the order of 10-12 m/day. For the near-inertial currents, the first two Empirical Orthogonal Functions (EOF) contribute only 40% into the total current variability for the period of LCE presence and 52% for the period of benign current conditions. The mode shapes vary within a wide range that, most likely, reflects a random distribution of mode shapes that depend on the lateral geometry of the forcing, mixed layer depth, and stratification.

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