Oil Sinking Research Articles

Mechanism of nearshore sediment-facilitated oil transport: New insights from causal inference analysis

A quantitative understanding of spilled oil transport in a nearshore environment is challenging due to the complex physicochemical processes in aqueous conditions. The physicochemical processes involved in oil sinking mainly include oil dispersion, sediment settling, and oil-sediment interaction. For the first time, this work attempts to address the sinking mechanism in petroleum contaminant transport using structural causal models based on observed data. The effects of nearshore salinity distribution from the estuary to the ocean on those three processes are examined. The causal inference reveals sediment settling is the crucial process for oil sinking. Salinity indirectly affects oil sinking by promoting sediment settling rather than directly affecting oil-sediment interaction. The increase of salinity from 0‰ to 35‰ provides a natural enhancement for sediment settling. Notably, unbiased causal effect estimates demonstrate the strongest positive causal effect on the settling efficiency of sediments is posed by increasing oil dispersion effectiveness, with a normalized value of 1.023. The highest strength of the causal relationship between oil dispersion and sediment settling highlights the importance of the dispersing characteristics of spilled oil to sediment-facilitated oil transport. The employed logic, a data-driven method, will shed light on adopting advanced causal inference tools to unravel the complicated contaminants’ transport.

The effect of hydrostatic pressure on the activity and community composition of hydrocarbon-degrading bacteria in Arctic seawater.

Increased ship traffic in the Arctic region raises the risk of oil spills. With an average sea depth of 1,000 m, there is a growing concern over the potential release of oil sinking in the form of marine oil snow into deep Arctic waters. At increasing depth, the oil-degrading community is exposed to increasing hydrostatic pressure, which can reduce microbial activity. However, microbes thriving in polar regions may adapt to low temperature by modulation of membrane fluidity, which is also a well-known adaptation to high hydrostatic pressure. At mild hydrostatic pressures up to 8-12 MPa, we did not observe an altered microbial activity or community composition, whereas comparable studies using deep-sea or sub-Arctic microbial communities with in situ temperatures of 4-5°C showed pressure-induced effects at 10-15 MPa. Our results suggest that the psychrophilic nature of the underwater microbial communities in the Arctic may be featured by specific traits that enhance their fitness at increasing hydrostatic pressure.

Impact of mixing energy and dispersant dosage on oil dispersion and sedimentation with microplastics in the marine environment

Recently, the fate of spilled oil in the presence of microplastics (MPs) in the sea has attracted attention of researchers. Merey crude oil and polyethylene terephthalate (PET) were used as the experimental materials in this study. The effects of mixing energy and dispersant dosage on oil dispersion and sedimentation in the presence of MPs in the water column were investigated by laboratory experiments simulating actual sea conditions. The increase of mixing energy showed a promoting effect on oil dispersion. When the oscillation frequency increased from 140 rpm to 180 rpm, the oil dispersion efficiency (ODE) ranged from 2.1 %–3.7 % to 17.4 %–30.8 %, and the volumetric mean diameter (VMD) of the suspended oil droplets/MPs-oil agglomerates (MOA) decreased from 99.9–131.4 μm to 76.6–88.2 μm after 2 h oscillation. The application of chemical dispersant led to an increase in both the quantity and size of the formed sunken MPs-oil-dispersant agglomerates (MODA). At the dispersant-to-oil ratio (DOR) of 1:5, the ODE declined from 77.7 % to 62.6 % when the MPs concentration increased from 0 to 150 mg/L, while the oil sinking efficiency (OSE) rose from 3.4 % to 15.6 % when the MPs increased from 25 to 150 mg/L; the maximum size of the sunken MODA reached 13.0 mm, and the total volume of the MODA formed per unit volume oil reached 389.7 μL/mL oil at the MPs concentration of 150 mg/L. Meanwhile, the results showed that the presence of MPs inhibited the oil dispersion by increasing the oil-water interfacial tension. The outcomes of this work may provide assistance in predicting the transport of spilled oil and developing emergency measures.

Formation of oil-particle aggregates in the presence of marine algae.

After an oil spill, the formation of oil-particle aggregates (OPAs) is associated with the interaction between dispersed oil and marine particulate matter such as phytoplankton, bacteria and mineral particles. Until recently, the combined effect of minerals and marine algae in influencing oil dispersion and OPA formation has rarely been investigated in detail. In this paper, the impacts of a species of flagellate algae Heterosigma akashiwo on oil dispersion and aggregation with montmorillonite were investigated. This study has found that oil coalescence is inhibited due to the adhesion of algal cells on the droplet surface, causing fewer large droplets to be dispersed into the water column and small OPAs to form. Due to the role of biosurfactants in the algae and the inhibition of algae on the swelling of mineral particles, both the oil dispersion efficiency and oil sinking efficiency were improved, which reached 77.6% and 23.5%, respectively at an algal cell concentration (Ca) of 1.0 × 106 cells per mL and a mineral concentration of 300 mg L-1. The volumetric mean diameter of the OPAs decreased from 38.4 μm to 31.5 μm when Ca increased from 0 to 1.0 × 106 cells per mL. At higher turbulent energy, more oil tended to form larger OPAs. The findings may add knowledge about the fate and transport of spilled oil and provide fundamental data for oil spill migration modelling.

A mesoscale assessment of sinking oil during dispersant treatment

Although much is known about the sinking of oil in marine environments, considerable gaps persist when modelling the oil sinking process. Scientific models are still needed to characterise the sunken oil and understand its mechanisms under various environmental conditions. In this study, a model is developed to investigate the sinking characteristics of oil with and without the effect of dispersant treatment. By coupling a Lagrangian particle module, a wave action module, a weathering module, and a droplet size variation module, the model is tested by experimental data obtained from a mesoscale wave tank (32 m × 0.8 m × 2 m). The influence of dispersant on the formation of small (d < d50) and large droplets (d ≥ d50) in the experimental oil is identified, and the contribution of dispersants to the effective sinking of oil is given by model simulation. The model results show that the addition of dispersants can significantly increase the amount of sunken oil, with the effect of dispersants being enhanced by wave action. The model establishes mechanisms to explain oil sinking characteristics, clarifying oil spill behaviour and providing new ideas for the dispersant treatment of sinking oil.

Performance of dispersed oil and suspended sediment during the oil-sediment aggregation process

Oil-sediment aggregation is an important transport and transformation process of spilled oil, which has been considered as a pathway of spill remediation. This work focused on the individual performance of dispersed oil and sediment during the aggregation process. Dispersion of three oils was first tested and validated in a water tank. An approach of estimating the mass variation of the sediment that has participated in forming the oil-sediment aggregates (OSAs) has been developed by density analysis. Results indicated that the density of the formed OSAs increases during the aggregation. In the context of remediation, it takes longer for sediment to reach equilibrium than for dispersed oil, especially under high mixing energy at a large sediment concentration, which results in the formation of dense OSAs, as well as high aggregation degree and rate. Roncador oil possesses a relatively high capability of capturing sediment to form dense OSAs, especially at an initial sediment concentration of over 150 mg/L. Oil sinking efficiency and the characteristic change rate of aggregated oil mass seem to be proportional to oil dispersion efficiency, and decrease with the mean size of dispersed oil droplets. The process of aggregation can further promote the dispersion of oil into water column. This study also provides fundamental data for the formation kinetics of OSAs.

Marine Oil Snow, a Microbial Perspective

Under certain conditions, dispersed crude oil in the sea combines with organisms, organic matter, and minerals to form marine oil snow (MOS), thereby contributing to the sinking of oil to the seafloor. Marine microbes are the main players in MOS formation, particularly via the production of extracellular polymeric substances. Distinct groups of microbes also consume the majority of the hydrocarbons during descent, leading to enrichment of the less bioavailable hydrocarbons and asphaltenes in the residue. Here we discuss the dynamics of microbial communities in MOS together with their impacts on MOS evolution. We explore the effects of dispersant application on MOS formation, and consider ways in which laboratory experiments investigating MOS formation can be more representative of the situation in the marine environment, which in turn will improve our understanding of the contribution of MOS to the fate of spilled oil.

Oil dispersion and aggregation with suspended particles in a wave tank

Suspended particulate matter (SPM) in marine environments plays an important role in determining the fate of spilled oil via the generation of oil-particle aggregates (OPAs). A series of mesoscale wave tank experiments and sedimentation tests were conducted to fill the knowledge gap on how the turbulent mixing, temperature, and oil type affect the dispersion of spilled oil and properties of OPAs. Generally, the oil dispersing efficiency was significantly enhanced by high wave energy, which also led to effective oil sinking, large size of OPAs and wide distribution of trapped oil. Nonlinear fitting results indicated that the oil sinking efficiency followed an exponential growth over time. The effect of temperature on oil dispersion and formation of OPAs is primarily attributed to its influence on oil viscosity and interfacial tension. Viscous oils are more likely to interact with particles above 25 °C. However, below 20 °C, a specific oil viscosity that will bring about the maximum OPAs exists. Excessive oil viscosity will lead to a weak binding between oil and SPM and a centralized distribution of trapped oil. Furthermore, spilled oil with a high asphaltene can interact more effectively with particles. Our finding suggested that early prevention of offshore oil sinking is key in summer.

Life under an oil slick: response of a freshwater food web to simulated spills of diluted bitumen in field mesocosms

Heavy crude oil transportation over land is increasing, yet the ecological impacts of spills, particularly of diluted bitumen, in freshwater environments remain poorly understood. We simulated spills of diluted bitumen in 1400 L land-based mesocosms containing water and sediments from a boreal, oligotrophic lake and monitored the response of natural planktonic communities over 11 days. Most species of phytoplankton (chrysophytes and dinoflagellates) and zooplankton (copepods and cladocerans) were sensitive to oil, exhibiting &gt;70% overall abundance reductions in response to the spills. Declines in nano- and microphytoplankton were short-lived and began to recover after the oil sank, whereas picophytoplankton and zooplankton populations remained depressed at the end of the experiment. In contrast, oil spills stimulated bacteria known to degrade hydrocarbons, especially Alphaproteobacteria, whereas Gammaprotobacteria (a common marine oil spill bacterial class) increased less. This is the first experiment to examine the effects of diluted bitumen in a multitrophic freshwater community.

Distribution of Polycyclic Aromatic Hydrocarbons in Sunken Oils in the Presence of Chemical Dispersant and Sediment

The formation of sunken oils is mainly dominated by the interaction between spilled oils and sediments. Due to their patchiness and invisibility, cleaning operations become difficult. As a result, sunken oils may cause long-term and significant damage to marine benthonic organisms. In the present study, a bench experiment was designed and conducted to investigate the quantitative distribution of polycyclic aromatic hydrocarbons (PAHs) in sunken oils in the presence of chemical dispersant and sediment. The oil sinking efficiency (OSE) of 16 priority total PAHs in the sediment phase was analyzed with different dosages of dispersant. The results showed that the synergistic effect of chemical dispersant and sediment promoted the formation of sunken oils, and the content of PAHs partitioned in the sunken oils increased with the increase of dispersant-to-oil ratios (DORs). Furthermore, with the addition of chemical dispersant, due to the solubility and hydrophobicity of individual PAHs, the high molecular weight (HMW) PAHs with 4–6 rings tended to partition to sediment compared with low molecular weight (LMW) PAHs with 2–3 rings. The synergistic effect of chemical dispersant and sediment could enhance the OSE of HMW PAHs in sunken oils, which might subsequently cause certain risks for marine benthonic organisms.

Thermal characteristics of waxy crude oil during its static cooling in an overhead pipeline

By means of additional specific heat capacity and momentum source term methods, the thermal characteristics of waxy crude oil during its static cooling in an overhead pipeline after shutdown are investigated by the numerical simulation. According to the different thermal performances, the cooling can be divided into three stages. In the first stage, the temperature distribution of stratification, the flow pattern of cold oil sinking and hot oil rising is the main performance. In the second stage, the isotherm in the pipeline changes from parallel line into ellipse shape, which implies that the natural convection is gradually replaced by heat conduction. During this stage, the gelled oil generates first at the bottom of the pipeline. And then it extends upward along the pipeline wall. In the last stage, the isotherm gradually becomes a concentric circular shape reflecting the characteristics of heat conduction. In this stage, the jelled boundary is approximately round shape, and the gelled structure is gradually pushed from the pipe wall to the center of the pipe. Furthermore, the detailed evolution characteristics of the temperature and convective heat transfer coefficient along the pipe wall are presented which are significantly influenced by the transition of the heat transfer mechanism.

OIL BEHAVIOUR AND THE RESPONSE TO A SUNKEN OIL SPILL OF SLURRY IN QUINTERO BAY, CHILE

ABSTRACT Slurry oils are one of the few groups of oils that have a density greater than full salinity seawater. Slurry spills at sea are rare, but when they do occur, the response can be difficult, with low final recovery rates. Oil spill response planning and recovery techniques have been refined over many years and the research and development of most methods has been underpinned by the principle that oil floats on water. This recent case study provides an example of the behavior of a slurry spill and the subsequent response operations. A leak of an API gravity 4° slurry occurred from a submarine pipeline in Quintero Bay, Chile, on 14th May 2016. The oil sank to the adjacent sea bed and covered an area of approximately 10,000 m2 in water depths of 18–22 m. The initial response involved over 20 dry-suit divers with surface air to recover the oil with vacuum hoses. These were then supplemented by four diver-operated vacuum dredges. Fortunately weak bottom currents did not redistribute the oil; nevertheless “sea bed booms” were deployed around the perimeter to prevent migration. These “booms” were initially a screen mesh that was later supplemented by sturdier metal frame screens deployed around the zone of the sunken oil in a zigzag configuration. Baseline benthic sediment samples were collected from the adjacent unaffected area and subsequently from the treatment area after completion of operations. A benthic SCUBA SCAT survey using a track-line positioning system was conducted to systematically document the distribution of the oil and post-treatment systematic ROV survey ensured that the end-point oiling conditions had been achieved.

Evaluation of Oil-Sediment Interactions and the Possibility of Oil Sinking in Marine Environments

ABSTRACT 2017-217 One of the major unknowns with respect to the fate and behavior of spilled dilbit is its state of buoyancy, particularly when mixed with sediments. What form do diluted bitumen and sediment mixtures take, and will they float or sink in water column? In this study, we evaluated the fate and behavior of Cold Lake Blend-Winter at three different weathering states (i.e., fresh, medium, and heavily weathered) in high-energy mixing marine conditions, with (and without) sufficient concentrations of sediments to ensure formation of oil-particulate aggregates (OPA). Conventional light crude oil and intermediate and heavy fuel oils were also included to serve as references for behavior of other types of oils. Two mineral sediments including kaolin (fine) and sand (coarse) as well as natural sediment from the Douglas Channel (DC) in northern British Columbia, (medium) were used for this evaluation. The resulting OPAs were characterized in terms of buoyancy, OPA density, particle size distribution, and morphology to better understand the oil-sediment interaction. In the absence of sediment, mixing of the oils with water resulted in meso/entrained–water-in-oil mixtures; these mixtures remained floating on the water surface. However, in presence of kaolin or the DC sediments, a significant portion of the OPA sank to the bottom of the water column for all oils, with the exception of the light crude oil and the highly weathered Cold Lake Blend-Winter. The later did not uptake as much sediment and instead formed discrete free-floating tarballs. In experiments with the larger sand sediment, no OPAs formed. The density and particle size analysis revealed that the OPAs of the oils with higher viscosity tended to have larger densities and particle sizes. Microscopic examination of the OPAs showed that all consisted of oil droplets surrounded by sediment particles and were present in single droplet or multiple-droplet clusters.

Engineering Reduced Graphene Oxide Aerogel Produced by Effective γ-ray Radiation-Induced Self-Assembly and Its Application for Continuous Oil–Water Separation

Reduced graphene oxide aerogel (RGO aerogel) is successfully synthesized via simultaneous reduction and self-assembly of graphene oxide (GO) sheets under γ-ray irradiation. As the resulting RGO aerogel possesses an interconnected macroporous structure with strong hydrophobicity and oleophilicity, it has great potential in oil–water separation. Adsorption–distillation and adsorption–combustion are both utilized to treat oil floating on water or oil sinking below the water surface. More importantly, a simple device has been developed to adsorb continuously and collect floating oil, and it has shown great promise for practical application.

Guidelines to Prepare for Oil Sands Product Spills in Varied Aquatic Environments

ABSTRACT On July 24, 2007, the Westridge Transfer Line in Burnaby, British Columbia, ruptured spilling 1,400 barrels of oil sands product into the area's storm water systems and eventually into the Burrard Inlet at Vancouver Harbor. The response to this spill was considered successful and there is no record of oil sinking. Several years later, in July of 2010, the Line 6B pipeline operated by Enbridge Energy Partners LLP ruptured spilling 20,082 barrels of oil sands product into the Kalamazoo River. In contrast to the Burnaby spill, this response was extremely difficult due to the sinking of large quantities of oil. The variance in fate and behavior of the oil sands products in these two spills demonstrates how environmental factors can result in different response challenges. Many environmental factors affect the fate of spilled oil sands products in aquatic environments because bitumen, a large component of oil sands products, has a density greater than freshwater. By analyzing specific factors in areas at risk, responders can better prepare for, and expect, submergence in oil sands product spills. Areas identified to have low salinity, rough sedimentation, high turbidity, strong sunlight exposure, high temperatures, and strong currents have a high risk of submergence. Response teams in these areas of high risk should have submerged oil recovery equipment readily available for rapid deployment.

Pool fires of transformer oil sinking into a rock bed

Experiments are reported on pool fires of transformer oil (flash point 157°C) burning over a rock bed in a 1.2 m diameter pan, with and without drainage from the bottom of the pan. Levels in the pool are referenced to the mean rock surface level (MRSL), defined as the horizontal plane (level of oil) where 50% of the area of the plane is broken by the surface rocks of the rock bed. Without drainage, using a rock type having a mass median diameter of 23 mm and with an initial oil level 51 mm above the MRSL, there was little change in heat release rate until the oil level regressed 25 mm below the MRSL; subsequently, the heat release rate fell sharply and continued at a low rate for >3 h, when the flames were extinguished manually. With drainage at regression rates of 16–26 mm/min, used in most of the experiments, there was no appreciable decrease in heat release rate until the oil regressed below the MRSL in this case, and the fires self-extinguished when the oil level dropped 23–29 mm below the MRSL, depending on rock type (two types investigated). Heat release rates during active combustion (∼ 570 kW/m2 convective) were little affected by oil drainage, the initial oil level, the preburn interval or the rock type in the ranges investigated.

CONDITIONS UNDER WHICH FLOATING SLICKS CAN SINK IN MARINE SETTINGS

ABSTRACT Ten spills were identified in which the oil initially floated, but eventually sank. In all cases, the oils were heavy residual products (such as No. 6 fuel oil) or heavy crudes. In seven of the cases, oil sank only after mixing with sand, by either stranding on the beach or mixing in the offshore surf zone. In two of the cases, oil sank after being heated during fires. In only one case was loss by evaporation proposed us the cause of the oil's not floating. Because incorporation of sediment (primarily sand) into the oil makes the oil-sediment mixture dense, the oil can separate from the mixture and refloat. It seems likely that the separation or settling out of the sand from the sand-oil mixture depends on the viscosity of the mix, and thus may depend on temperature.

OIL IN NEARSHORE SUBTIDAL SEDIMENTS OF SAUDI ARABIA FROM THE GULF WAR SPILL

ABSTRACT Detailed sedimentological and dynamic-process studies of the shallow, subtidal habitats of Dawhats ad Dafi and al Mussallamiyah and the bays at Tanaqib on the Saudi Arabian coast were carried out one year after the Gulf War oil spill. These studies were part of Leg II of the NOAA ship Mt. Mitchell cruise. Satellite imagery and space shuttle photography were used extensively to develop detailed study plans. Work accomplished during the study included deployment of three current meters, a tide gauge, and suspended sediment traps (at seven locations). Bathymetric surveys were conducted along 14 transects, and 197 bottom observation dives were carried out. More than 170 bottom sediment samples were collected for chemical and/or textural analysis. Sediment hydrocarbon screening by HPLC fluorescence was conducted on board to verify and refine the sampling plan. The results to date show no evidence of large-scale sinking of oil as a result of the spill. Subtidal oil, as sparse tar balls, was visually observed by divers at three locations, all of which were associated with the erosion of oiled sand from outer beaches. On-board chemical results showed that subtidal sediments have been contaminated at levels ranging from 20 to 2,000 mg/kg petroleum hydrocarbons, with the highest contamination up in the sheltered, muddy basins. However, the oil initially stranded in the intertidal zone does not appear to be accumulating in the nearshore subtidal region in significant quantities one year later.

Contamination of nearshore subtidal sediments of Saudi Arabia from the Gulf War oil spill

Detailed sedimentological and dynamic-process studies of the shallow, subtidal habitats along on the Saudi Arabian coast were carried out 1 year after the Gulf War oil spill, as part of the NOAA ship Mt Mitchell cruise. Satellite imagery and space shuttle photography were used to characterize the subtidal habitats and select sampling sites. A total of 197 bottom-observation dives were carried out, and 170 bottom sediment and sediment trap samples were collected for chemical analysis. The results show no evidence of large-scale sinking of oil from the spill. Detailed chemical results showed that surficial subtidal sediments (0–5 cm) have been contaminated at levels ranging from <5 to 900 μg g −1 total hydrocarbons (THC), with the highest contamination in sheltered, muddy basins. In these basins, total PAHs were in the range of 1–7 μg g −1. Little contamination was observed below 5 cm. The oil that had initially stranded in the intertidal zone was not accumulating in the nearshore subtidal region in significant quantities 1 year later.

OIL SPILL CONTROL AND ABATEMENT TECHNIQUES USED AT THE S.S. SANSINENA EXPLOSION SITE—A COAST GUARD PERSPECTIVE1

ABSTRACT At 1938 PST on Friday, December 17, 1976, the Liberian tankership Sansinena exploded and burned while taking on ballast at the Union Oil Terminal, Berth 46, Los Angeles harbor, California. In addition to the loss of nine lives and millions of dollars in property damage, approximately 30,000 barrels of oil was spilled onto Los Angeles harbor waters. The majority of this oil sank to the bottom of the harbor and had to be removed mechanically over the following sixteen months utilizing oil removal equipment designed and constructed especially for this spill. Two years after the Sansinena disaster the reconstructed Union Oil Terminal is in full operation, with only an occasional small oil sheen stirred from the bottom by propwash to remind us of the havoc of that December Friday.