Petroleum Platforms Research Articles

Temporal and Spatial Relationships of Yellowfin Tuna to Deepwater Petroleum Platforms in the Northern Gulf of Mexico

AbstractIn 2006–2007, 110 Yellowfin Tuna Thunnus albacares were tagged with acoustic transmitters near deepwater oil platforms and one drillship in the northern Gulf of Mexico off the Mississippi River delta to determine the extent to which platforms act as fish aggregating devices (FADs). Vemco acoustic receivers were installed on six deepwater platforms to detect the presence of tagged individuals. Five of 12 Yellowfin Tuna captured in 2006 were detected in 2007, demonstrating multi‐year presence in the region. Ninety Yellowfin Tuna were detected in 2007, resulting in 221 platform residencies and 32 single detections. Duration of residence at a platform was positively correlated with the platform's depth, and the number of transitions decreased with platform‐to‐platform distance. In total, 109 movements between platforms by 46 (51%) different individuals were detected, traveling distances of up to 98.2 km. Yellowfin Tuna displayed interactions with deepwater platforms in the northern Gulf of Mexico similar to their interactions with FADs and other studied geological features, by way of aggregating or using them as meeting points, landmarks, and stopovers within a movement corridor. The large number of oil and gas platforms located in the northern Gulf of Mexico may have a significant effect on distribution, retention, and migration of Yellowfin Tuna populations in this area of the gulf.

Assessing the size spectra of marine fish communities with hydroacoustics: examining the challenges of abundant schools, diverse assemblages, and variable orientations

Assessing marine fish community size spectra with hydroacoustics is challenging, as communities are diverse, schooling and swim-bladder-less fishes are common, and fish orientation is variable. We developed an approach to examine these challenges and applied it to data from 51 optic–acoustic surveys of fishes at petroleum platforms throughout the US Gulf of Mexico. When in situ target strength (TS; dB re 1 m2) distributions were used to calculate the density (and subsequently abundance) of schooling fishes, fish lengths and size spectra slopes were significantly smaller than in simulated communities and fish community censuses at platforms (i.e., reference datasets). However, acoustic slopes were comparable to reference slopes when simulated TS values (based on species composition) were used to calculate schooling fish abundance. These findings held regardless of whether specific or general models were used to convert TS to length. Fish orientation was not a useful predictor of TS or slope, but may explain why in situ TS measurements from small groups of fishes around schools were unsuitable for abundance calculations. By examining the challenges associated with assessing size spectra with acoustics, this study aids progress towards using acoustic size spectra metrics for ecological inferences.

Centralized power generation with carbon capture on decommissioned offshore petroleum platforms

The existing cogeneration systems on offshore petroleum platforms face clashing targets intrinsic to offshore applications, namely, weight, area, cost and efficiency. Moreover, the prolonged offdesign operating conditions during their lifetime further increase the inefficiencies, leading to increased environmental impact. Thus, in this work, centralized power stations are designed for supplying the electricity required by various identical floating production, storage and offloading units (FPSOs) in the offshore oil and gas sector. This approach aims to increase the performance and alleviate the environmental burden that the conventional utility systems are responsible for by integrating carbon abatement technologies. Since these modifications bring about an increase in the initial investment cost and the financial feasibility of the system, a techno-economic assessment and optimization process is necessary in order to determine the optimal configuration of the power hubs. To this end, a combined thermodynamic, environmental and economic analysis, together with space and weight allowance quantification is performed. The use of adapted and decommissioned FPSOs for installing the power hub is a novel proposal that reduces the initial investment cost. As a result, the advanced utility systems provide higher overall power generation efficiencies (above 10 percentage points) compared to existing simple cycle gas turbine systems, even at fourfold lower emissions. The incremental economic analysis has found that, for moderate carbon taxations (> 40 USD/tCO2), the advanced power generation systems may economically outperform the conventional offshore power plants. Lastly, a delay in entry of operation between FPSOs of up to 4 years may reduce the investment cost by 50%, while maintains the same thermodynamic performance.

Absolute Abundance Estimates for Red Snapper, Greater Amberjack, and Other Federally Managed Fish on Offshore Petroleum Platforms in the Gulf of Mexico

AbstractOffshore petroleum platforms provide habitat utilized by an array of reef fish that are valuable to both commercial and recreational fishers. However, thousands of offshore platforms have been decommissioned in the Gulf of Mexico over the past decade, with many of the removals being accomplished using explosive severance methods. Here, we estimate the impact of platform removal in the Gulf of Mexico on five stocks of federally managed reef fish based on the percentage of each stock that is resident on platforms. We conclude that the gulfwide impact of removal will be relatively minor (1% to 8% of the estimated stock abundance) for four species, Red Snapper Lutjanus campechanus, Gray Triggerfish Balistes capriscus, Vermilion Snapper Rhomboplites aurorubens, and Cobia Rachycentron canadum. In contrast, losses for the Greater Amberjack Seriola dumerili stock would potentially represent 45% of the known stock. An alternative explanation is that the actual abundance of Greater Amberjack is much larger than the most recent stock size estimate; in either case, we suggest this issue needs further examination. Removal impacts could also be significant for reef‐fish fisheries (especially the Red Snapper fishery) in areas where platforms are presently abundant but other high‐relief natural or artificial reefs are not present. Removal of the platforms from these areas will greatly impact the local fisheries.

Multi-functional epoxy composite coating incorporating mixed Cu(II) and Zr(IV) complexes of metformin and 2,2\-bipyridine as intensive network cross-linkers exhibiting anti-corrosion, self-healing and chemical-resistance performances for steel petroleum platforms

Metal-organic network cross-linking agents are commingled with epoxy for establishing multi-functional coating system with robust resistance properties for steel protection applications in harsh atmospheres. To support this concept, the present study relates to fabrication of new mixed ligand Cu(II) and Zr(IV) complexes of metformin (MF) and 2.2′bipyridine (bpy) as coating surface cross-linking modifiers to guard the steel surface of petroleum platforms from corrosion in severe environments. CHN analysis, molar conductance, magnetic susceptibility, FT-IR, UV–Visible, 1 H NMR and TGA/DTG analysis were performed for full characterizations of the two ligands and their mixed complexes. The elemental analysis data affirmed the chemical formula of the formed complexes. Molar conductance measurements proved that the complexes were electrolytic in nature with 1:2 (metal:ligand) molar ratio. The FT-IR analysis for MF, bpy and their complexes manifested that MF and bpy chelated with metal ions as bidentate ligands through two imines (-C = NH) groups in MF and through two nitrogen of pyridine rings in bpy. The TGA/DTG analysis demonstrated the thermal stability and decomposition of the complexes. The magnetic moment measurements offered paramagnetic properties for Cu(II), μ eff = 1.70 B.M. The structure geometry survey affirmed a distorted octahedral geometry of the formed Cu(II) and Zr(IV) complexes. Epoxy coating formulations loaded with the same concentration of MF, bpy, Cu(II), and Zr(IV) compounds were applied and evaluated. Salt spray corrosion trial demonstrated that PA-DGEBA/MC-Cu coating achieved advanced corrosion mitigation demeanor at blistering size of #8, few frequency and calculated rust grade at 10. SEM morphology and EDX analysis were performed to explicate the protective performance in which PA-DGEBA/MC-Cu coated layer displayed the least Fe peak count at 2.5 without appearance of rusting. AFM microstructure of surface-modified Cu(II) epoxy coating offered the most smooth surface (Ra = 1.78 nm, Rq = 2.99 nm), with a harder matrix and perfect nonporous coating surface. Acid spot test checked the chemical resistance of these coatings and elucidated that DGEBA/MC-Cu coating achieved the highest acid resistances at Level 0 by H 2 SO 4 (96%), HNO 3 (70%) and HCl (37%) against full deterioration of blank neat epoxy at Level 3.

Optic–acoustic Analysis of Fish Assemblages at Petroleum Platforms

Petroleum platforms provide high‐relief reef habitat in several ocean basins and are important to fishes and fishers alike. To determine which variables were important for shaping platform‐associated fish assemblages on a basin‐wide scale in the U.S. Gulf of Mexico, we employed optic and acoustic methods to measure fish distribution (geographic and water‐column), abundance, biomass, density, size, diversity, and richness at 54 platforms. We found that variables related to freshwater inflow and meso‐scale circulation patterns (e.g., salinity) affected more metrics than platform characteristics (e.g., platform depth). Platform fish assemblages varied gradually along gradients of these variables instead of exhibiting distinct assemblage groupings in non‐metric multidimensional scaling space. These effects contributed to the presence of biomass, density, diversity, and richness “hotspots” at platforms offshore of the Atchafalaya River. Our findings underscore the importance of freshwater inflow and circulation patterns in explaining variation in reef fish assemblages in the U.S. Gulf of Mexico.

Optimal design of power hubs for offshore petroleum platforms

Even though advanced power generation systems offer higher efficiencies than simpler gas turbines, severe area and weight restrictions keep on impeding their widespread implementation in offshore petroleum industry. If those restrictions could be resolved, the performance of the utilities systems on offshore platforms may be drastically enhanced. In order to overcome these practical limitations, the installation of a power hub is proposed to centralize the energy supply required by a number of floating production, storage and offloading units (FPSOs). However, many challenges are still brought to companies contemplating this approach, such as incremental costs and prolonged offdesign operating conditions. This circumstance renders necessary to determine the optimal number, layout and operating load of the modular power units on the hub. Thus, in this work, a computational framework is developed to assist in the selection of the most suitable hub setups, so that the trade-off between higher overall efficiency and lower investment cost can be elucidated. This framework consists of a group of subroutines that evaluates, compares and ranks alternative offshore utility systems in terms of well-defined objective functions, whereas is subject to restricted weight and space allowances. As a result, the power hub configurations based on the largest bottoming cycles benefit from the economies of scale, as well as from an increased efficiency, if compared to other designs based on smaller bottoming cycles. Levelized costs of electricity reaches 40 USD/MWh when only gas turbines are installed, which can be reduced by 13% if combined cycles are preferred. The weight-to-power ratio of the hubs based on combined cycles remains 12–28% higher than that of the conventional setup, whereas the efficiency increase achieves up to 7 percentage points.

Characterizing the second wave of fish and invertebrate colonization of an offshore petroleum platform

Abstract Offshore Oil and Gas (O&G) infrastructure affords structurally complex hard substrata in otherwise featurless areas of the seafloor. Opportunistically collected industrial ROV imagery was used to investigate the colonization of a petroleum platform in the North Sea 1–2 years following installation. Compared to pre-construction communities and pioneering colonizers, we documented 48 additional taxa, including a rare sighting of a pompano (Trachinotus ovatus). The second wave of motile colonizers presented greater diversity than the pioneering community. Occurrence of species became more even over the 2 years following installation, with species occurring in more comparable abundances. No on-jacket sessile taxa were recorded during first-wave investigations; however, 17 sessile species were detected after 1 year (decreasing to 16 after 2). Motile species were found to favour structurally complex sections of the jacket (e.g. mudmat), while sessile organisms favoured exposed elements. Evidence of on-jacket reproduction was found for two commercially important invertebrate species - common whelk (Buccinum undatum) and European squid (Loligo vulgaris). Moreover, abundance of larvae-producing species experience an 8.5-fold increase over a 2-year period compared to baseline communities. These findings may have implications for decommissioning and resource-management strategies, suggesting that a case-by-case reviewing approach should be favoured over the most common “one size fits all”.

Understanding patterns of fish backscatter, size and density around petroleum platforms of the U.S. Gulf of Mexico using hydroacoustic data

Hydroacoustic surveys were conducted at 56 different oil and gas platforms in the U.S. Gulf of Mexico (GOM), along with a commensurate collection of physio-chemical data, in order to characterize patterns of fish distribution around platforms. Relative acoustic measurements of Mean Volume Backscatter “MVBS”, Target Strength “TS” and fish density were examined. These acoustic variables were employed to test if patterns of MVBS, TS and density around GOM platforms differed among seabed depth-based categories (Coastal: 0-30 m; Offshore: 31-60 m; Bluewater: >60 m), and how these patterns varied as a function of the distance to platforms. The acoustic measurements were also examined across the study area to determine the influence of specific environmental factors and platform features (using generalized additive mixed models (GAMMs)), and whether hypoxic waters compressed fish distribution in the water column. Significantly greater mean fish densities and MVBS occurred at Coastal sites and these variables decreased with increasing seabed depth, whilst mean TS was highest at Offshore sites. Greatest values of fish MVBS and density were found at the shortest distances (0-25 m) from platforms. GAMMs suggested that salinity and temperature had a significant effect on fish density, TS, and MVBS. The number of other platforms within 5 km also had a significant effect on MVBS. Dissolved oxygen concentration has a significant effect on fish density. Finally, we found that fish densities and MVBS were significantly higher in the depth layers immediately above hypoxic layers, demonstrating vertical compression of fishes in the water column when hypoxia occurs. Our findings provide further evidence of the influence of environmental conditions and platform features on the regional patterns of fish density, TS and MVBS around platforms, and the influence of platforms on these metrics on a local scale across the GOM. The study highlights the applicability of using hydroacoustics in conjunction with modelling to assess fish distributions around artificial habitats.

Microbial diversity of the glass sponge Vazella pourtalesii in response to anthropogenic activities

Establishment of adequate conservation areas represents a challenging but crucial task in the conservation of genetic diversity and biological variability. Anthropogenic pressures on marine ecosystems and organisms are steadily increasing. Whether and to what extent these pressures influence marine genetic biodiversity is only starting to be revealed. Using 16S rRNA gene amplicon sequencing, we analysed the microbial community structure of 33 individuals of the habitat-forming glass sponge Vazella pourtalesii, as well as reference seawater, sediment, and biofilm samples. We assessed how two anthropogenic impacts, i.e. habitat destruction by trawling and artificial substrate provision (moorings made of composite plastic), correspond with in situ V. pourtalesii microbiome variability. In addition, we evaluated the role of two bottom fishery closures in preserving sponge-associated microbial diversity on the Scotian Shelf, Canada. Our results illustrate that V. pourtalesii sponges collected from protected sites within fishery closures contained distinct and taxonomically largely novel microbial communities. At the trawled site we recorded significant quantitative differences in distinct microbial phyla, such as a reduction in Nitrospinae in the four sponges from this site and the environmental references. Individuals of V. pourtalesii growing on the mooring were significantly enriched in Bacteroidetes, Verrucomicrobia and Cyanobacteria in comparison to sponge individuals growing on the natural seabed. Due to a concomitant enrichment of these taxa in the mooring biofilm, we propose that biofilms on artificial substrates may ‘prime’ sponge-associated microbial communities when small sponges settle on such substrates. These observations likely have relevant management implications when considering the increase of artificial substrates in the marine environment, e.g., marine litter, off-shore wind parks, and petroleum platforms.

Comparative assessment of advanced power generation and carbon sequestration plants on offshore petroleum platforms

On conventional offshore petroleum platforms, the combined heat and power production (CHP) currently depends on simple cycle gas turbine systems (SCGT) that operate at lower efficiency and increased environmental impact compared to modern onshore thermoelectric plants. Additionally, the reduced space and the limited weight budget on offshore platforms have discouraged operators from integrating more efficient, but also bulkier cogeneration cycles (e.g. combined cycles). In spite of these circumstances, more stringent environmental regulations of offshore oil and gas activities have progressively led to a renewed interest in the integration of advanced cogeneration systems, together with either customary or unconventional carbon capture approaches, to maintain both higher power generation efficiencies and reduced CO2 emissions. Thus, in this paper, it is evidenced how advanced gas turbine concepts are promising technologies for maintaining or even increasing efficiency, while facilitating the capture rate of CO2 produced, either for geological storage or enhanced oil recovery. Despite the profuse research works on onshore applications, advanced cogeneration and carbon capture systems have been barely studied in the context of supplying power to offshore petroleum platforms. Accordingly, the performance of a conventional offshore petroleum production platform (without carbon capture system) is compared to other configurations, based on either an amine-based chemical absorption system or oxyfuel combustion concepts ( S-Graz and Allam cycles) for CO2 capture purposes. Since the original power and heat requirements of the processing platform must remain satisfied, an energy integration analysis is performed to determine the waste heat recovery opportunities. Additionally, the exergy method helps quantifying the most critical components that lead to the largest irreversibility and identifying the thermodynamic potential for enhanced cogeneration plants. As a result, oxyfuel equipped platforms provide a diversified set of advantages, while keeping competitive efficiencies. For instance, advanced systems allow for cutting down ostensibly the atmospheric CO2 emissions compared to the conventional and amine-based power plant configurations of the FPSO.

Changes in Shrimping Effort in the Gulf of Mexico and the Impacts to Red Snapper.

Despite a complex management landscape and decades of overfishing, Red Snapper (Lutjanus campechanus) stocks have grown substantially in the Gulf of Mexico and restrictions on the fisheries that catch them are being loosened. This year, annual shrimping effort was allowed to increase by 21% after National Marine Fisheries Service scientists concluded that the resulting bycatch of Red Snapper would only reduce the annual allowable catch in other fisheries by ∼1% and have no impact on population growth. Nonetheless, the recreational fishing sector intensely campaigned against this rule, fueled by wild mischaracterization of shrimp trawl bycatch in media outlets targeting anglers. Here, we aim to elevate the debates surrounding Red Snapper management by presenting scientific and historical context for the potential impacts from shrimping. We discuss our views of the current problems facing Red Snapper and key ecological questions to address for more effective management of this resource.

Environmental and Structural Drivers of Fish Distributions among Petroleum Platforms across the U.S. Gulf of Mexico

AbstractPetroleum platforms in the U.S. Gulf of Mexico (GOM) are important habitats for fishes and support regional fisheries. However, drivers of the horizontal (i.e., latitudinal and longitudinal) and vertical (i.e., position in the water column) distribution patterns of fishes associated with these artificial habitats are not fully understood on a GOM‐wide scale. To build upon previous studies on a large spatial scale and focus on species‐specific drivers, we conducted 114 submersible rotating drop‐camera and water quality sonde surveys at 54 platforms throughout the GOM. We then fitted two sets of binomial generalized additive mixed models integrating environmental and structural (i.e., characteristics of platforms) predictors to encounter/nonencounter data for 17 fish species so as to understand their horizontal and vertical distribution patterns throughout the GOM in platform habitat. Significant predictors for horizontal distribution included distance from shore (for Bermuda Chub Kyphosus saltatrix, Greater Amberjack Seriola dumerili, Vermilion Snapper Rhomboplites aurorubens), salinity (Bermuda Chub, Red Snapper Lutjanus campechanus), the number of platforms within 5 km (Blue Runner Caranx crysos, Crevalle Jack Caranx hippos), and dissolved oxygen concentration (Red Snapper). Significant predictors for vertical distribution included temperature (for Atlantic Spadefish Chaetodipterus faber, Bermuda Chub, Blue Runner, Greater Amberjack, Red Snapper), salinity (Greater Amberjack, Red Snapper), dissolved oxygen concentration (Red Snapper), and seafloor depth (Red Snapper). However, the majority of the study species were not influenced by the predictors included in the horizontal (11 of 17 species) and vertical distribution (12 of 17 species) generalized additive mixed models. Thus, many GOM fishes were found to associate with platforms over a relatively wide range of environmental conditions and platform characteristics. This suggests specific environmental conditions and distinct platform characteristics may not be as important as the simple number of available platforms for determining the distributions of many platform‐associated fishes in the GOM.

Developing a Hybrid Data-Driven, Mechanistic Virtual Flow Meter - a Case Study

Virtual flow meters, mathematical models predicting production flow rates in petroleum assets, are useful aids in production monitoring and optimization. Mechanistic models based on first-principles are most common, however, data-driven models exploiting patterns in measurements are gaining popularity. This research investigates a hybrid modeling approach, utilizing techniques from both the aforementioned areas of expertise, to model a well production choke. The choke is represented with a simplified set of first-principle equations and a neural network to estimate the valve flow coefficient. Historical production data from the petroleum platform Edvard Grieg is used for model validation. Additionally, a mechanistic and a data-driven model are constructed for comparison of performance. A practical framework for development of models with varying degree of hybridity and stochastic optimization of its parameters is established. Results of the hybrid model performance are promising albeit with considerable room for improvements.

Site fidelity, vertical movement, and habitat use of nearshore reef fishes on offshore petroleum platforms in southern California

Off California, economically important nearshore reef fishes inhabit the shallow (<20 m) regions of offshore petroleum platforms on the San Pedro Shelf (SPS). It is essential to understand the degrees to which platforms support fish over time to indicate whether biological requirements (e.g., shelter, diet, reproduction) are being met. To determine the ecological importance of platforms as fish habitat, the site fidelity and depth/habitat use of adult cabezon, Scorpaenichthys marmoratus (Ayres, 1854), grass rockfish, Sebastes rastrelliger (Jordan and Gilbert, 1880), kelp rockfish, Sebastes atrovirens (Jordan and Gilbert, 1880), and California sheephead, Semicossyphus pulcher (Ayres, 1854) were investigated at platforms Edith (50 m bottom depth) and Eureka (212 m). A total of 63 fish were acoustically tagged and monitored for up to 578 d. Sixty-three percent of individuals were still present at platforms at the end of the study (long-term site fidelity), with 55 individuals detected a mean of 66.9% (SD 36.0%) of their total days at liberty (daily site fidelity). All species displayed a shift in seasonal depth use. The shallowest horizontal level, consisting of various horizontal beams at platform Edith (15 m depth) and Eureka (17 m), was the most utilized habitat by grass rockfish, kelp rockfish, and California sheephead. Cabezon at platform Eureka utilized depths (21–31 m) unassociated with horizontal levels, while at platform Edith they primarily utilized the second horizontal level (30 m). Decommissioning options that remove the shallowest 26 m of structure would eliminate the habitat most utilized by three of the four study species that dominate the nearshore reef fish communities at SPS platforms.

Being prepared for emergencies: a virtual environment experiment on the retention and maintenance of egress skills

The retention of safety-critical egress skills is an essential part of emergency preparedness on offshore petroleum platforms. Virtual environment (VE) training has been shown to be an effective method for teaching basic onboard familiarization and offshore emergency evacuation procedures. This technology has the potential to train crews before they are deployed offshore. This paper investigates the long-term retention and maintenance of emergency egress competence obtained using a virtual offshore platform. In particular, the research aimed to answer two questions: (1) what egress skills can be remembered after a period of 6 months? and (2) how effective is a VE-based retraining program at maintaining egress skills? A two-phased experiment was designed to first teach basic egress skills and subsequently assess skill retention after a 6- to 9-month period. The first phase of the experiment used a simulation-based mastery learning (SBML) pedagogical approach to teach naïve subjects the necessary spatial and procedural skills to evacuate safely. In the second phase of the experiment, the same 36 participants were tested after the retention interval on their ability to respond to a series of egress test scenarios. Participants who had trouble remembering the egress procedures were provided retraining on deficient skills. The results of the experiment indicate that emergency egress skills (both spatial and procedural knowledge) are susceptible to skill decay. This paper will highlight the skills that were most susceptible to skill fade after a period of 6 to 9 months and discuss the efficacy of the retraining participants received to return to competence.

Exergy assessment and energy integration of advanced gas turbine cycles on an offshore petroleum production platform

On offshore platform applications, power and heat are normally supplied by simple open cycle gas turbine (OCGT) and heat recovery steam generators (HRSG) at lower efficiencies if compared to onshore combined cycle systems. Certainly, due to the reduced available space and the weight constraints, combined cycles are not commonly considered as cogeneration systems on conventional offshore petroleum platforms. However, more stringent environmental policies for the natural gas and oil production activities have motivated the integration assessment of advanced technological solutions that aim to mitigate the environmental impact that conventional offshore platforms are responsible for. Accordingly, in this paper, the effect of the integration of a low emission, oxyfuel gas turbine cycle is analyzed and compared against an amines-based post-combustion system and a conventional offshore petroleum platform operation in terms of its exergy efficiency and reduced atmospheric CO2 emissions. Indeed, although the conventional configuration is the most efficient, the oxyfuel powered platform configuration presents close power cycle efficiency of 27.10% and the lowest specific CO2 emissions of 0.014 kgCO2/toil, whereas the amines-based layout provides the best cogeneration efficiency (55.34%) of the advanced configurations. Moreover, an energy integration analysis is performed to identify the heat recovery potential, while the exergy method is used to evaluate and quantify the most critical components that lead to the largest irreversibilities along the primary separation, cogeneration and gas compression systems. As a result, the study points to ways of decarbonizing offshore applications in the oil and gas sector.

Numerical Modelling and Analysis of Factors Influencing Bearing Capacity of Skirt Foundation

Skirt foundations have been discovered to be one of the alternatives to stacking offshore structures such as wind turbines, petroleum platforms etc. Offshore wind turbines are primarily exposed to vertical and lateral loads due to wind and present conditions. Many scientists have already carried out multiple vertical loading experiments on a circular footing and have found that this category of foundation increases bearing ability, decreases settlement and changes the behavior of load settlement. In this study, a 3D finite element analysis is carried out to evaluate how the skirt foundations are influenced by the vertical loads. The soil medium and skirt foundation were designed for analyses with varying in their aspect ratios (change in dimensions of depth, d and diameter, D) of skirt foundation and area ratio of skirt foundation. The effect of compactness of soil medium is also calculated by using various types of soil parameters. Furthermore, the current results express how the load carrying capacity of skirt foundation is varied by changing in the aspect ratios and area ratios of the skirt foundation. Also conclusions were drawn that compactness of soil medium plays a vital role in carrying vertical load.

Documenting deepwater habitat utilization by fishes and invertebrates associated with Lophelia pertusa on a petroleum platform on the outer continental shelf of the Gulf of Mexico using a remotely operated vehicle

Marine communities associated with oil and gas platforms beyond the continental shelf are poorly described islands of potential interaction between structure oriented and pelagic taxa. Near-bottom, biological surveys were conducted at a petroleum platform located in 305 m water depth off the coast of Louisiana between 268 m and the seabed. Surveys were performed with a remotely operated vehicle (ROV) and consisted of replicated benthic transects on all four sides of the platform extending 125 m outward from the platform. The fouling community on hard surfaces of the horizontal cross-members and verticals were surveyed using HD video and digital still images. Relative abundances of fishes were estimated using digital still images collected at regular intervals under three illumination regimes: no light, red light, and white light, while the ROV hydraulics were switched off to reduce vehicle noise. Additional surveys of fishes were conducted during day and night at the platform and at two far-field sites located 2 km and 3 km from the platform by monitoring species attracted to buckets containing an olfactory attractant. The results indicated abundant coldwater coral Lophelia pertusa present on the platform and on the surrounding rubble near the platform. The fish assemblage at the platform was dominated by American barrelfish Hyperoglyphe perciformis, greater amberjack Seriola dumerili, Darwin's slimeheads Gephyroberyx darwinii, snowy grouper Epinephelus niveatus, misty grouper Hyporthodus mystacinus, American conger Conger oceanicus and Scorpaenidae. The fish community at the farfield site was substantially different and less diverse than that observed at the platform and was dominated by king snake eels (Ophichthys rex) and Scorpaenidae. The results indicate that multiple methods and both day and night surveys are necessary to obtain a more complete picture of the biological community around platforms located on the outer continental shelf. The use of red-filtered lights and quiet surveys without hydraulic pumps on can further reduce avoidance artifacts.

Characterizing the first wave of fish and invertebrate colonization on a new offshore petroleum platform

Abstract Offshore Oil & Gas (O&G) infrastructure creates artificial reef complexes that support marine communities in oceans. No studies have characterized the first wave of colonization, which can reveal information about habitat attraction and ecological connectivity. Here we used opportunistically-collected industrial Remotely Operated Vehicles (ROVs) to investigate fish and invertebrate colonization on a new North Sea O&G platform and trenching of an associated pipeline. We observed rapid colonization of fish communities, with increases in species richness (S), abundance (N), and diversity (H′) over the first four days (the entire study period). By contrast, there was minimal change in motile invertebrate communities over the survey period. After trenching, invertebrate S, N and H′ decreased significantly, whilst fish S, N and H′ increased. This study is the first to report on the pioneer wave of fish and invertebrate colonization on O&G infrastructure, thereby providing rare insight into formation of new reef communities in the sea. These short and opportunistic data are valuable in terms of showing what can be discovered from analysis of ‘pre-installation’ ROV footage of O&G structures, of which there are terabytes of data held by O&G companies waiting to be analyzed by environmental scientists.