Wind profile and structure is critical in design of offshore structures such as oil/gas platforms or wind farm turbines. Since 2017, three ZX 300M wind vertical profiling LIDAR (Light Distance and Ranging) systems have been installed on two TLPs (Tension Leg Platform) and one Semi-submersible in the Mississippi Canyon in the Gulf of Mexico. The LIDAR system measures wind profile from 10m to up to 200m above deck. This paper presents the wind profile data and analysis from these measurements for several severe storms that passed through the region. It is hoped that this data will provide insights into the structure of the turbulent hurricane boundary layer, to help the design of wind sensitive offshore structures and their components. First, the wind profile time series were divided into small segments of data, then the profile of mean wind speeds, turbulence intensities and gust factor across the wind column were calculated. The measured mean wind profiles, turbulence intensities, peak gust factors are then compared to the Frøya wind profile and time-averaging relations as suggested by ISO 19901-1:2015 and API RP 2MET as well as the formulation given in Engineering Science Data Unit (ESDU) models. These comparisons are used to understand the applicability of the wind models to offshore hurricane conditions and assess the design principles of offshore structures.

Abstract Hurricane Ida made landfall in Port Fourchon, Louisiana, as a Category 4 hurricane on August 29th, 2021, traveling over some offshore oil and gas facilities on its path. Shell Exploration and Production's offshore oil and gas installations in the Gulf of Mexico (GoM) have the most comprehensive suite of metocean instrumentation in the region, including wave and wind systems that captured the passage of hurricane Ida. This paper analyzes the wind and wave conditions measured by some Shell facilities located along the path of hurricane Ida. The number of LiDAR wind profilers and their spatial distribution with respect to Ida makes Shell the only operator in the Gulf of Mexico able to provide a detailed vertical wind profile at multiple locations throughout the extreme wind event. These observations, combined with satellite products such as Sea Surface Height (SSH) and Sea Surface Temperature (SST), help understand the hurricane track and intensity. Three Shell Tension Leg Platforms (TLPs) and one Semi-Submersible offshore Louisiana, measured wave data, with an overall maximum wave height of 21 m and a maximum significant wave height of 13 m. Two Shell TLPs and one Semi-Submersible measured wind profiles with maximum wind speeds of 46.82 ms−1 (91 knots, 104 mph), 43.52 ms−1 (84 knots, 97 mph), and 39.95 ms−1 (77 knots, 89 mph). Out of those three Platforms, the two sites that captured the strongest wind speeds were located right on Ida's path, where it was possible to record the wind direction shift as Hurricane Ida passed over the, and the third site was east of the track.

API SC2 has issued integrity management recommended practices to compliment the planning, design and construction standards that has led to a GOM installed base of 50 floating production facilities. Integrity management involves risk-based inspections in which the collection and analysis of characteristic and conditional data determines if integrity can be assured. The challenge to manage unstructured data with the same design and construction approaches yields inefficient and repetitive activities that can be time-consuming and may lead to a less optimal outcome. The primary objective of the study is to understand the benefits of utilizing a digitized IM approach which involves high resolution metocean data to determine fatigue damage accumulation for tendons and risers instead of traditional design/assessment methods that use condensed metocean criteria data.

This paper describes the development and installation of an ocean surface current monitoring device called SCINS: Surface Current Imaging Nowcast System. We describe the process of designing and building the prototype system, installation on an offshore platform, implementation of real-time reporting, and results from one year of operations. SCINS utilizes passive long-wave infrared imaging of the ocean to derive surface currents. This is done using a time-series of images to observe the phase-speed of the ocean waves. Then, the Doppler shift of the observed waves due to the surface current is determined using a non-linear least squares fit. The primary components of SCINS are a long-wave infrared camera and a data acquisition computer. The camera is mounted several 10s of m above the water surface. The system collects imagery at 2 Hz for 5 minutes every 15 minutes, day and night, and calculates surface currents in real-time. In this paper, we describe the results from deploying SCINS on an offshore platform, Chevron's Big Foot TLP, in the Gulf of Mexico for one year of continuous data collections, including several tropical storm and hurricane events. Results are compared to environmental data to describe system performance as a function of wind, wave, and sea conditions. We describe the engineering challenges and lessons learned from designing and installing this new type of passive imaging system for offshore use. We conclude that SCINS is an effective method for measuring surface currents in the vicinity of offshore platforms, requiring very little maintenance and without the need to put any instrumentation in the water.

We seek to characterize the behavior of extreme waves in the Gulf of Mexico, using a 109 year-long wave hindcast (GOMOS). The largest waves in this region are driven by strong winds from hurricanes. Design of offshore production systems requires the estimation of extreme metocean conditions corresponding to return periods from 1 year to 10,000 years and beyond. For extrapolation to long return periods, estimation using data for around 100 years from a single location will incur large uncertainties. Approaches such as spatial pooling, cyclone track-shifting and explicit track modeling have been proposed to alleviate this problem. The underlying problem in spatial pooling is the aggregation of dependent data and hence underestimation of uncertainty using naïve analysis; techniques such as block-bootstrapping can be used to inflate uncertainties to more realistic levels. The usefulness of cyclone track-shifting or explicit track modeling is dependent on the appropriateness of the physical assumptions underpinning such a model. In this paper, we utilize a simple spatial statistical model for extreme value estimation of significant wave height under tropical cyclones, known as STM-E, proposed in Wada et al. (2018). The STM-E model was developed to characterize extreme waves offshore Japan, also dominated by tropical cyclones. The method relies on the estimation of two distributions from a sample of data, namely the distribution of spatio-temporal maximum (STM) and the exposure (E). In the current work, we apply STM-E to extreme wave analysis in Gulf of Mexico. The STM-E estimate provides a parsimonious spatially-smooth distribution of extreme waves, with smaller uncertainties per location compared to estimates using data from a single location. We also discuss the estimated characteristics of extreme wave environments in this region.

In 2005 the Department of the Interior, through the Minerals Management Service (MMS), issued a Notice to Lessees (NTL No. 2005-G05) requiring collection of ocean current speed and direction profiles in active oil and gas exploration and production sites. The NTL stipulates that ocean current profiles be collected down to 1000 meters (from ∼ 30 meters) at a minimum of 20 minute intervals and be delivered to the Department of Commerce, National Oceanic and Atmospheric Administration's National Data Buoy Center (NOAA NDBC) at a minimum interval of 12 hours. Available technology at the time was largely limited to acoustic Doppler current profiling (ADCP) instruments manufactured by Teledyne RD Instruments (TRDI). By default, these instruments have been virtually the sole mechanism of data collection in the Gulf of Mexico until recently. The complete NDBC database of ocean current measurements stretches back to 2005 for many of the installations and contains mid to upper level current measurements of immediate (e.g., operational thresholds, search and rescue, etc.) and long term application (e.g., riser fatigue analysis, large scale ocean dynamic studies, etc.). Though the data has been quality controlled in regards to the current magnitude measurements, verification of the direction profiles has been identified as problematic. RPS Evans Hamilton Inc. (RPS) and Shell Global Solution Inc. (Shell) recently entered into a collaboration to assess the quality and variation of the water column ocean current data collected on Shell assets. While the measurements of ocean current velocity appear to be robust, the current direction time series from many of the installations on drill ships exhibit full water column variation over very short timescales that are likely not representative of the environmental conditions. These anomalies manifest as full-profile shifts in current direction spanning the full range of heading measurements (0–360 degrees). The shifts do not appear to be correlated with physical phenomena in the area of data collection but do appear to correlate with changes in the floating platform's operational heading. The scale and deviation of the shifts vary widely and randomly, with no correlation to the measured instrument heading change observed by the onboard motion reference unit (MRU). RPS and Shell Metocean have hypothesized that the anomalies exhibited in the current direction measurements may originate in the onboard MRU utilized by the above-mentioned ADCPs to determine relative heading for transformation of the measured raw beam velocity data. To test this hypothesis, a true north-seeking fiber optic MRU has been added to the deployment configuration on one of the Shell drill ships. Initial results indicated that the fiber optic MRU heading measurements were much more stable and did not exhibit the radical variation observed in the onboard MRU during repositioning of the floating drillship. Post-processing of the raw beam velocity data using the recorded fiber optic MRU output completely eliminated the anomalous shifts in water column current direction profiles and agreed well with independent measurement and synoptic scale predictions.

This paper reports on the implementation of real-time processing in the Remote Ocean Current Imaging System (ROCIS). ROCIS exploits time-space processing of airborne ocean wave imagery to produce maps of surface currents. ROCIS may enable new understanding of ocean processes and be employed to provide improved regional ocean forecasts.

Abstract As part of the Bureau of Ocean Energy Management, Regulation and Enforcement(BOEMRE) sponsored study for ocean current monitoring from 500 - 1,000 metersin the Gulf of Mexico, this paper describes the methodology and results ofassessing the characteristics of the forcing and occurrence of elevated currentevents. BOEMRE NTL ADCP data, historical mooring current data and three types ofPrinceton Regional Ocean Forecasting System (PROFS) model data were used forthis study. Based on the analysis of current characteristics, ocean currentkinetic energy distribution and observational data availability, fourrepresentative zones are indentified. For each zone, the long term and eventcurrent profile characterizations and subsurface elevated event screening areundertaken, and long- and short-term full water column current profilecharacterizations (representative current profiles and associatedprobabilities) are derived from selected quality controlled NTL ADCP data, historical mooring data and PROFS model data. These current profiles andspecific riser models for each type (Drilling, SCR, TTR, Hybrid Risers, and TLPTendons) are used to assess the VIV damage, which is documented in theaccompanying paper by Ozturk et al. (OTC 23570). This study will evaluate the significance of ocean currents in water depthsbetween 500 and 1000 meters on riser and mooring systems, as well as toidentify whether any significant events have resulted. The study results willhelp BOEMRE to define whether monitoring below 500 meters is justifiable inregards to fatigue analysis of riser or mooring systems. 1. INTRODUCTION Safe and efficient exploration and development of deepwater offshore oil andgas fields require the development of a comprehensive knowledge of the localoceanographic current regime. The study of ocean current monitoring from 500 -1,000 meters in the Gulf of Mexico was sponsored by the Bureau of Ocean EnergyManagement, Regulation and Enforcement (BOEMRE) of the U.S. Department of theInterior. The purpose of this study was three-fold:Assess the characteristics of Gulf of Mexico current forcing in the 500 to1,000 meter range and occurrence of elevated events;To evaluate the significance of ocean currents in water depths between 500and 1000 meters on the fatigue and design of risers, moorings and TLPtendons;Based on the findings, to form a recommendation on whether monitoring below500 meters is justifiable in regards to fatigue analysis of riser or mooringsystems. This paper describes the activities associated with the first purpose of thestudy. The accompanying paper by Ozturk et al. (OTC 23570) addresses theremaining goals.

In 2008 a pioneering bathymetric LIDAR survey of the Torres Straits was undertaken. Due to the ever finer spatial details in the data and complex tidal regime, extensive water level data was collected at 19 stations to allow the reduction of the LiDAR survey data. A model with the ability to provide the water level at any location and instance in time was developed to replace the traditional tidal correction method of discrete tide zoning. This paper presents the results of this data collection program and describes techniques that were used to analyze and predict water levels in the region, which are some of the most complex ever monitored.

Abstract The HYCOM (HYbrid Coordinate Ocean Model) consortium, sponsored by the National Ocean Partnership Program (NOPP), provides near real time global estimates of daily mean current data back to November 2003. In April 2005, the US Minerals Management Service (MMS) issued a Notice to Lessees and Operators (NTL) regarding the reporting of ocean current data in the deep water of Gulf of Mexico. An extensive body of NTL current data has since been collected by the offshore oil and gas industry and made available via the National Data Buoy Center (NDBC) web site. This provides an extremely valuable source of observational data for current model validation at deepwater drilling locations in the Gulf of Mexico. Careful validation of the HYCOM model is required to ensure critical features of the current regime are adequately represented and to assess model skill. The paper describes the methodology and results of a HYCOM current model validation exercise using the MMS NTL observations in the Gulf of Mexico. The suitability of the model for the offshore industry in Gulf of Mexico is discussed. Introduction As the offshore industry is moving to ever-deeper waters, assessment of the ocean current is required. The knowledge of the ocean currents through depth is essential to riser design and control, operation of Dynamically Positioned Vessels, and other elements of engineering design and operation of deepwater oil and gas facilities. The Hybrid Coordinate Ocean Model (HYCOM) consortium is a multi-institutional effort funded by the National Ocean Partnership Program (NOPP), as part of the U. S. Global Ocean Data Assimilation Experiment (GODAE), to develop and evaluate a data-assimilative hybrid isopycnal-sigma-pressure (generalized) coordinate ocean model (called HYbrid Coordinate Ocean Model or HYCOM). The horizontal dimensions of the global grid are 4500 × 3298 grid points resulting in ~7 km spacing on average. There are up to 32 vertical layers, depending on the water depth, with output at standard Levitus depth levels. Daily data are available from 3 November 2003 to three days into the future (Chassignet et al., 2009). On April 21, 2005, the US Minerals Management Service (MMS) issued a Notice to Lessees and Operators (NTL) regarding the reporting of ocean current data in the deep water of Gulf of Mexico. Since then, the offshore oil and gas industry has collected and reported current data, using Acoustic Doppler Current Profilers (ADCPs), at 78 deep water drilling locations in the Gulf of Mexico. The extensive body of NTL ADCP current data has been made available via the National Oceanic and Atmospheric Administration (NOAA) National Data Buoy Center (NDBC) web site1. This provides an extremely valuable source of observational data for model validation at deepwater drilling locations in Gulf of Mexico. Based on the results of the HYCOM validation in the Gulf of Mexico, this study assesses the suitability of the model for application by the offshore industry in the Gulf of Mexico.

Abstract Since strong bottom currents with long durations have been observed in many deepwater developments, scour hazards may become a serious concern which can have major consequences for pile foundations and associated equipment. While bridge scour has been studied and well documented, offshore scour prediction remains an uncertain art. In most cases, local experience is relied on as the best guide for scour prediction, and an operating strategy of monitoring and remediation is considered necessary. This can result in excessive contingencies and design allowances and the need for expensive and time consuming monitoring. In this paper, selected bridge scour concepts are extended to apply to deepwater pile scour prediction after necessary modifications. Pile behaviors with the presence of scour are studied, to identify the sensitive scour range for various types and sizes of offshore piles. Introduction There has been a rapid growth in the number of structures installed in deepwater. Considering the tremendous investment and the extremely harsh environment that are associated with offshore projects, foundations of offshore structures have to meet very stringent requirements. In current offshore foundation design practice, one of the common and plaguing issues is how to select the appropriate scour parameters and evaluate the scour effect. The presence of seabed scour " affects both lateral and axial pile performance and capacity?? as stated in API RP 2A-WSD (2005). However, " scour prediction remains an uncertain art. The sediment transport studies may assist in defining scour design criteria but local experience is the best guide. The uncertainty on design criteria should be handled by robust design or by an operating strategy of monitoring and remediation as needed.?? Scour is the erosive action of flowing water, which excavates and carries away materials from streambeds and banks. It is a very complex process involving soil, flow and the geometry characteristics of structures placed in the flow path. These three elements by themselves are also defined by many variables. Scour is initiated when the flow generated bed shear stress is larger than a threshold value of the soil erosion resistance, which is known as the soil critical shear stress (tc). A chart showing the typical value of critical shear stress for various soils was developed by Briaud el al (1999) and is presented in Fig 1. Around a foundation, the total scour usually is comprised of general scour and local scour. The general scour occurs on an open seabed where the flow itself is strong enough to erode away the seabed materials and is expressed by seabed scooping in a relatively large area. Local scour involves removal of material from around structures placed in the flow path and is caused by the acceleration of flow and resulting vortices induced by the flow obstruction. Development of local scour is presented as a scour hole around the foundation. Fig 2 shows a local scour developed around a cylindrical pile in cohesive soils studied in Texas A&M University by Briaud et al (2003). It is known that scour in cohesive soils (clays) differs from that in loose granular materials (sand/silt) mostly by the slow erosion rate. Under a constant flow, while it may take hours to reach the maximum scour depth in sands, weeks and months of time is required to complete the same process in clays.

There have been reports of strong submerged jet currents in the Gulf of Mexico in recent years which have implications for the design and operation of some offshore facilities. This paper describes the methodology and results of a screening study which searched for such events within the extensive body of recent data collected by the offshore oil and gas industry, made available on the NOAA National Data Buoy Center web site. This study was conducted on behalf of a consortium of industry clients with participation by relevant US government bodies. After a first phase investigation, initially well defined screening criteria were revised to avoid the numerous events triggered by clearly invalid data and the potential for missing some critical submerged events. The automatic screening criteria were replaced by manual event selection based on plots showing all available data. The identified events fall into the following broad categories: • Submerged speed peaks due to inertial period currents, most notable after the 2005 hurricanes. • A few submerged jet like events isolated in time with no clear periodicity. • Submerged speed peaks with high vertical and error velocities and often incoherent structures. • Persistent high speed currents near the limit of the ADCP range.

A recent screening study of MMS NTL ADCP 2005 and 2006 data has identified two modes of submerged jet currents in the Gulf of Mexico: (1) submerged speed peaks with inertial period and (2) events isolated in time with no clear periodicity. The latter can be divided further as shallow jet events (between 150m to 600m) and deep jet events (deeper than 600m). The submerged jet events can last a few hours to several days. In order to investigate the jet generation mechanisms and test the predictability of the events, representative events for each mode were studied. Satellite sea surface height (SSH), sea surface temperature (SST) data and forecast data of the Princeton Regional Ocean Forecast System (PROFS) during the selected events have been used. Mode 1 jets are mainly due to downward propagating of inertial oscillations following hurricanes, while the deep jets of mode 2 appear to be caused by deep current propagation along the 1000m isobath. The shallow jets of mode 2 are the result of on-slope flow convergence producing a subsurface downwelling/upwelling cell and frontogenesis over the slope. The comparison of PROFS model and observations shows good predictive skill although the model has the tendency to underestimate current strengths.

Coast-hugging surface flood plumes occur on the inner shelf of northern California during the winter season, generating dense, near-bottom suspensions which may attain fluid mud concentrations as particles settle. The period of storm-heightened waves may continue into the flood period, leading to gravity-driven seaward displacement of the bottom suspension; or the wave regime may ameliorate, leaving the suspension to consolidate as a short-lived, inner-shelf flood bed. Such beds tend to be resuspended within days or weeks by subsequent storm events that may recreate the original high concentrations. The sediment is thus dispersed seaward by gravity flows, to be deposited as a muddy flood bed on the central shelf. The locus of deposition of these “high-concentration regimes” is a function of the relative intensities of river discharge and storm wave height. Greater discharge piles thicker storm beds nearer shore, while intense wave regimes allow deposition of the fluid mud further seaward. During events with high values of both parameters, large amount of fluid mud may bypass over the shelf edge. In contrast, “low-concentration regimes” occur during storm periods when there has been no recent flood deposition on the inner shelf. The shelf floor is better consolidated than in the previous case, and the resulting suspended sediment concentrations are lower. As a consequence, low-concentration regimes are winnowing and bypassing regimes, and the beds deposited are thinner and sandier. Algorithms describing deposition by high and low-concentration regimes have been embedded in a probabilistic model. A simulation of a 400-year sequence of beds deposited by winter storms and floods suggests that on the Eel shelf, the Holocene transgressive systems tract consists of back-stepping, seaward-fining event beds, whose timelines (bedding planes) dip more gently than do their gradational facies boundaries. At these longer time scales, flood beds dominate over storm beds.

Drifter and satellite data are assimilated into a circulation model that hindcasts near-surface currents in the Northeastern Gulf of Mexico. Experiments without assimilation, and using assimilation of drifter, satellite sea-surface height (SSH) and sea-surface temperature (SST) data, in various combinations, were conducted. Currents derived from these experiments were used to compute drifter trajectories that were compared against observations. Surface geostropic current fields, calculated from satellite SSH, were also used to generate drifter paths. Assimilation that used a combination of drifter and satellite data reproduced the drifter trajectories with position errors ≈30–80 km over a 10-day period. Comparisons of the modeled currents with moored observations on the West Florida shelf show improvement when data assimilation is used, because of better simulation of deepwater processes (primarily the loop current).

通过对废黄河河口水下三角洲海域水文、泥沙、沉积和地形的调查分析,对组成水下三角洲-10--15m以深的平坦海床、-5--10m间的水下斜坡、-5m以浅的近岸浅滩三个地貌单元的水动力特征以及在波流和潮流作用下底部泥沙冲刷率的横向分布进行计算分析,并建立了水下三角洲地形横向剖面地形的演变预测模式.结果表明,在三角洲不同地貌单元内,由于所处不同的水动力条件和底部泥沙特性,出现了不同的侵蚀状态,其中在-10--15m以深的平坦海床,除了3m以上的大浪外,水动力作用以强劲的潮流冲刷为主,目前已接近冲刷相对平衡的状态;在-5--10m间的水下斜坡,受波浪和潮流的共同作用,冲刷强度大,地形剖面呈继续平行后退状态;-5m以浅的近岸浅滩,潮流作用相对较弱,以波浪对滩面的刷低为主,水深线不断向岸方向移动、滩宽变窄;0m以上的潮间带滩地,则波浪和潮流作用均较弱,近岸高滩接近相对稳定状态,有利于海岸线的工程防护.

A two-dimensional, across-shelf sediment-transport model has been developed to simulate storm deposition on continental shelves. This paper describes the structure of the model and related algorithms. In the model, the time-dependent sediment resuspension, transportation and deposition, and across-shelf transport gradients are simulated as responses to storm waves on the Eel shelf, northern California. The simulations show that the pattern of storm deposition on the sandy inner shelf is different from that on the muddy middle and outer shelf. Storm-bed thickness decreases seaward across the inner-shelf sandy zone as far as the 50-m isobath. Farther seaward, storm-bed thickness increases as the mud component in the sea floor becomes abundant, then decreases again, as the weakening of bottom-wave motion with greater depth becomes the dominant control. Storm-bed thickness in the mud zone thus has a nearly symmetrical cross-shelf pattern, with the maximum thickness at a water depth of 70 m. The pattern suggests that while the sequence of new beds found in February 1995 on the Eel shelf may have had a flood source, their geometry reflects storm resuspension and transport. The new muds found in these beds may have been reworked, transported and redeposited several times by storm waves and other oceanic forces. Numerical simulations illustrate that the critical bottom shear stress for mud erosion, τe, and the coefficient for sand resuspension, γ0, are more important than other parameters in determining storm depositional patterns on the Eel shelf.

<span id="ChDivSummary" name="ChDivSummary" class="abstract-text">废黄河口三角洲的演化主要表现为水下三角洲大面积的冲蚀和三角洲海岸线的夷平,形成了由—10m以深的平坦海床、—5m^—10m间的水下斜坡和—5m以浅的近岸浅滩三个地貌单元构成的地形格局。—10m^—15m水下平台稳定,略有冲刷;而水下斜坡随着往复性潮流长轴与斜坡走向逐渐趋于一致,潮流侧向侵蚀弱化;近岸浅滩则表现为人工护岸条件下的有限下切。这为深水港口的建设提供了良好的近岸水深条件和相对稳定的水陆域环境。</span>