Computer Modeling of Oil Spill Trajectories With a High Accuracy Method

This paper proposes a high accuracy numerical method to model oil spill trajectories using a particle-tracking algorithm. The Euler method, used to calculate oil trajectories, can give adequate solutions in most open ocean applications. However, this method may not predict accurate particle trajectories in certain highly non-uniform velocity fields near coastal zones or in river problems. Simple numerical experiments show that the Euler method may also introduce artificial numerical dispersion that could lead to overestimation of spill areas. This article proposes a fourth-order Runge–Kutta method with fourth-order velocity interpolation to calculate oil trajectories that minimize these problems. The algorithm is implemented in the OilTrack model to predict oil trajectories following the “Nissos Amorgos” oil spill accident that occurred in the Gulf of Venezuela in 1997. Despite lack of adequate field information, model results compare well with observations in the impacted area.     

Remote sensing of ocean surface currents with the Seasonde HF radar

The SeaSonde high-frequency radar is a portable, shore-based system for measuring ocean surface currents in real time over coverage areas exceeding 1000 km². It utilizes compact antennas and direction finding methods to extract information on currents from the sea echo signals. Experiments with the radar in sheltered coastal waters in Canada and oceanic conditions in the Pacific Ocean have shown reasonable agreement with drifters and current meters. Forecasting methods have been developed that provide estimates of the slowly varying flows produced by tide, wind and buoyancy, and estimates of the spatially varying eddy diffusivity, based on a few days of measurements. These current data are suitable for use in oil spill models.     

Probable Effects of Langmuir Circulation Observed on Oil Slicks in the Field

Although the presence of Langmuir circulation (LC) cells is evident from observations in lakes, ponds, and coastal waters, the effects of these cells on oil slicks have received less attention. This paper considers the effects as inferred from field data of LC cells on oil slicks. Examples from observed experimental oil slicks in the field are presented. The importance of these LC cells is discussed from the point of view of oil spill contingency.     

Comparative occurrence rates for offshore oil spills

Estimates of occurrence rates for offshore oil spills are useful for analysis of potential oil spill impacts and for oil spill response contingency planning. As the Oil Pollution Act of 1990 (U.S. Public Law 101–380, 18 August 1990) becomes fully implemented, estimates of oil spill occurrence will become even more important to natural resource trustees and to responsible parties involved in oil and gas activities. Oil spill occurrence rate estimates have been revised based on U.S. Outer Continental Shelf platform and pipeline spill data (1964–1992) and worldwide tanker spill data (1974–1992). These spill rates are expressed and normalized in terms of number of spills per volume of crude oil handled. The revisions indicate that estimates for the platform spill occurrence rates declined, the pipeline spill occurrence rates increased, and the worldwide tanker spill occurrence rates remained unchanged. Calculated for the first time were estimates of tanker and barge spill rates for spills occuring in U.S. waters, and spill occurrence rates for spills of North Slope crude oil transported by tanker from Valdez, Alaska. All estimates of spill occurrence rates were restricted to spills greater than or equal to 159 m³ (1000 barrels).     

Quantitative analysis of alternate oil spill response strategies using OSCAR

A three-dimensional numerical model of the physical and chemical behavior and fate of spilled oil has been coupled to a model of oil spill response actions. This coupled system of models for Oil Spill Contingency and Response (OSCAR), provides a tool for quantitative, objective assessment of alternative oil spill response strategies. Criteria for response effectiveness can be either physical (‘How much oil comes ashore?’ or ‘How much oil have we recovered?’) or biological (‘How many biologically sensitive areas were affected?’ or ‘What exposures will fish eggs and larvae experience in the water column?’). The oil spill combat module in the simulator represents individual sets of equipment, with capabilities and deployment strategies being specified explicitly by the user. The coupling to the oil spill model allows the mass balance of the spill to be affected appropriately in space and time by the cleanup operation as the simulation proceeds. An example application is described to demonstrate system capabilities, which include evaluation of the potential for both surface and subsurface environmental effects. This quantitative, objective approach to analysis of alternative response strategies provides a useful tool for designing more optimal, functional, rational, and cost-effective oil spill contingency solutions for offshore platforms, and coastal terminals and refineries.     

Removal of Oil from the Sea Surface through Particulate Interactions: Review and Prospectus

The fate of oil spilled in coastal zones depends in large part on the interactions with environmental factors existing within a short time of the spill event. In addition to weathering which produces changes in the chemistry of the hydrocarbon stock, physical interactions between oil and suspended particulate matter (SPM), both organic and inorganic, play a role in determining the dispersal and sedimentation rates of the spill. This in turn affects the degradation rate of the oil. This paper provides a comprehensive literature review of the role of oil–particle interactions in removal of petroleum hydrocarbons from the sea surface and provides estimates of the degree to which SPM may augment the deposition of oil. Both field and laboratory observations have shown widely varying rates of oil removal due to particulate interactions. The discussion covers the interaction between oil weathering, injection, sinking, adsorption, microbial processes, flocculation and ingestion by zooplankton, which all contribute to packaging oil and SPM into settling aggregates.     

The Social and Political Meaning of the Exxon Valdez Oil Spill

In this paper we argue that the Exxon Valdez oil spill gained so much attention because of its setting in Alaska. Alaska symbolizes for many Americans the wilderness or frontier that has long been part of American thought. At the same time, American national development has largely depended on the discovery and use of the nation’s abundant natural resources. The setting of the Valdez spill in the seemingly pristine waters of Prince William Sound brought the tension between our national identification with wilderness and our national need for further natural resource exploitation into sharp focus. In the aftermath of the spill, a legislative deadlock was passed and the Oil Pollution Act of 1990 was passed. The Valdez accident had longer-term consequences as well, most prominent of which is related to the ongoing debate over whether to open up the coastal plain in the Arctic National Wildlife Refuge to further development.     

Introduction/Overview to In Situ Burning of Oil Spills

In situ burning is an oil spill response technique or tool that involves the controlled ignition and burning of the oil at or near the spill site on the surface of the water or in a marsh (see Lindau et al., this volume). Although controversial, burning has been shown on several recent occasions to be an appropriate oil spill countermeasure. When used early in a spill before the oil weathers and releases its volatile components, burning can remove oil from the waters surface very efficiently and at very high rates. Removal efficiencies for thick slicks can easily exceed 95% (Advanced In Situ Burn Course, Spiltec, Woodinville, WA, 1997). In situ burning offers a logistically simple, rapid, inexpensive and if controlled a relatively safe means for reducing the environmental impacts of an oil spill. Because burning rapidly changes large quantities of oil into its primary combustion products (water and carbon dioxide), the need for collection, storage, transport and disposal of recovered material is greatly reduced. The use of towed fire containment boom to capture, thicken and isolate a portion of a spill, followed by ignition, is far less complex than the operations involved in mechanical recovery, transfer, storage, treatment and disposal (The Science, Technology, and Effects of Controlled Burning of Oil Spills at Sea, Marine Spill Response Corporation, Washington, DC, 1994).However, there is a limited window-of-opportunity (or time period of effectiveness) to conduct successful burn operations. The type of oil spilled, prevailing meteorological and oceanographic (environmental) conditions and the time it takes for the oil to emulsify define the window (see Buist, this volume and Nordvik et al., this volume). Once spilled, oil begins to form a stable emulsion: when the water content exceeds 25% most slicks are unignitable. In situ burning is being viewed with renewed interest as a response tool in high latitude waters where other techniques may not be possible or advisable due to the physical environment (extreme low temperatures, ice-infested waters), or the remoteness of the impacted area. Additionally, the magnitude of the spill may quickly overwhelm the deployed equipment necessitating the consideration of other techniques in the overall response strategy (The Science, Technology, and Effects of Controlled Burning of Oil Spills at Sea, Marine Spill Response Corporation, Washington, DC, 1994; Proceedings of the In Situ Burning of Oil Spills Workshop. NIST. SP934. MMS. 1998, p. 31; Basics of Oil Spill Cleanup, Lewis Publishers, Washington, DC, 2001, p. 233). This paper brings together the current knowledge on in situ burning and is an effort to gain regulatory acceptance for this promising oil spill response tool.     

Oil outflow estimates for tankers and barges

Results of an analysis to estimate potential oil outflow from tankers in the event of groundings and collisions is presented. Three baseline tanker types are considered: pre-MARPOL (COW), MARPOL '73 (SBT only), MARPOL '73/'78 (PL/SBT) before and after these tankers have been retrofitted with various combinations of pollution prevention measures. Specifically the analysis examines four tanker sizes, 46 600, 71 000, 152 000 and 268 000 dwt, and various pollution measures — protectively located spaces (PL/spaces) in various ballast arrangements and with clean ballast tanks (CBTs), hydrostatically balanced loading (HBL), probabilistically located HBL, combinations of HBL and PL/spaces, double bottom or double side retrofits, and replacement of the tanker with a double hull vessel. Additionally, oil outflow estimates are presented for a US coastal and an ocean going barge of over 5000 gt with and without PL/spaces, PL/SBT, and HBL. The accidental oil outflow estimates are developed in accordance with probabilistic and deterministic models of IMOs MARPOL Annex I Regulations 13F and 13G. The accidental oil outflow estimates presented in the paper may provide oil spill response and related organizations with information to assist in planning for oil spill response activities.     

The Svalbard Intertidal Zone: A Concept for the Use of GIS in Applied Oil Sensitivity,Vulnerability and Impact Analyses

Historical oil spills have shown that environmental damage on the seashore can be measured by acute mortality of single species and destabilisation of the communities. The biota, however, has the potential to recover over some period of time. Applied to the understanding of the fate of oil and population and community dynamics, the impact can be described by the function of the following two factors: the immediate extent and the duration of damage. A simple and robust mathematical model is developed to describe this process in the Svalbard intertidal. Based on the integral of key biological and physical factors, i.e., community specific sensitivity, oil accumulation and retention capacity of the substrate, ice-cover and wave exposure, the model is implemented by a Geographical Information System (GIS) for characterisation of the habitat’s sensitivity and vulnerability. Geomorphologic maps and georeferenced biological data are used as input. Digital maps of intertidal zone are compiled, indicating the shoreline sensitivity and vulnerability in terms of coastal segments and grid aggregations. Selected results have been used in the national assessment programme of oil development in the Barents Sea for priorities in environmental impact assessments and risk analyses as well as oil spill contingency planning.     

Langmuir Circulation and the Dispersion of Oil Spills in Shallow Seas

Aspects of Langmuir circulation (Lc) which relate to the dispersion of floating material are reviewed. These include convergence, dispersion by advection (particularly of a plume of floating oil when wind and current are in different directions) and the spread and dispersion by cell instability or breakdown first described by Csanady. There are, however, processes which compete with Lc to diffuse floating material. In shallow tidally mixed seas, where the environmental impact of an oil spill may be greatest, cross-wind dispersion caused by Lc will dominate over that produced by bottom turbulence if the ratio of the wind speed, W, to current, U, is sufficiently large. Observations and rough estimates suggest a transition near W/U=15. A simple model is devised to estimate cross-wind dispersion in shallow unstratified waters when turbulence generated at a flat seabed dominates that produced by Lc, but when the effects of Lc are still evident in aligning filaments of oil, as may commonly be the case in moderate winds in coastal or continental shelf waters.     

An approach to evaluate the application of the vulnerability index for oil spills in tropical Red Sea environments

The Egyptian national marine oil pollution contingency plan was urgently initiated after the Nabila oil spill in 1982, to provide an estimate of its environmental effects on the Egyptian Red Sea coastal areas and to determine geomorphological features and cuastal processes, together with physical, chemical and biological baseline data for this tropical environment.The ‘Vulnerability Index’ (VI) was applied to evaluate and calibrate the effect of the Nabila oil spill on the Egyptian Red Sea Coastal area. A detailed in situ coastal survey was conducted during two visits in November 1982 and May 1983 to 80 shore sites from Suez to Ras Banas to monitor the oil pollution and to apply the ‘Vulnerability Index’. A comparative assessment of the index over time by comparing it with a quick ground inspection in November 1993 to some sites to evaluate the applicability of this index for oil spills in such environments. In addition, the physical effects of fresh and weathered crude oil and/with dispersant on water filtration by different beaches were preliminary studied.The geomorphological/Vulnerability Index results show that most of the Egyptian Red Sea coastal environments have medium to high vulnerability to immediate and medium term oil spill damage. The oil pollution spread estimated to be 250 km south of the oil spill and about 200 km north of it. The quantity of oil along the shoreline was reduced by about 60% due to natural and authorities clean up. The third survey after 11 years showed that the VI could be used as a predictive tool for assessment of oil spill effects on such tropical environments.     

Update of Comparative Occurrence Rates for Offshore Oil Spills

Estimates of occurrence rates for offshore oil spills are useful for analyzing potential oil-spill impacts and for oil-spill response contingency planning. With the implementation of the Oil Pollution Act of 1990 (US Public Law 101-380, August 18, 1990), estimates of oil-spill occurrence became even more important to natural resource trustees and to responsible parties involved in oil and gas activities.Oil-spill occurrence rate estimates have been revised based on US Outer Continental Shelf (US OCS) platform and pipeline spill data (1964 through 1999), worldwide tanker spill data (1974 through 1999), and barge spill data for US waters (1974–1999). These spill rates are expressed and normalized in terms of number of spills per volume of crude oil handled. All estimates of spill occurrence rates were restricted to spills greater than or equal to 1000 barrels (159 m³, 159 kl, 136 metric tonnes, 42,000 US gallons).The revisions compared to the previously published rates calculated through 1992 (Anderson and LaBelle, 1994) indicate that estimates for the US OCS platform spill occurrence rates continue to decline, primarily because no spills have occurred since 1980. The US OCS pipeline spill occurrence rates for spills greater than or equal to 1000 barrels remained essentially unchanged. However, the rate for larger OCS pipeline spills (greater than or equal to 10,000 barrels) has decreased significantly. Worldwide tanker spill rates, rates for tanker spills in US waters, and rates for barge spills in US waters decreased significantly. The most recent 15-year estimates for 1985–1999 (compared to rates for the entire data series) showed that rates for US OCS platforms, tankers, and barges continued to decline.     

Stochastic Modeling Concepts in Groundwater and Risk Assessment: Potential Application to Marine Problems

Parameter uncertainty is ubiquitous in marine environmental processes. Failure to account for this uncertainty may lead to erroneous results, and may have significant environmental and economic ramifications. Stochastic modeling of oil spill transport and fate is, therefore, central in the development of an oil spill contingency plan for new oil and gas projects. Over the past twenty years, several stochastic modeling tools have been developed for modeling parameter uncertainty, including the spectral, perturbation, and simulation methods. In this work we explore the application of a new stochastic methodology, the first-order reliability method (FORM), in oil spill modeling. FORM was originally developed in the structural reliability field and has been recently applied to various environmental problems. The method has many appealing features that makes it a powerful tool for modeling complex environmental systems. The theory of FORM is presented, identifying the features that distinguish the method from other stochastic tools. Different formulations to the reliability-based stochastic oil spill modeling are presented in a decision-analytic context.     

Water-in-oil emulsion formation: A review of physics and mathematical modelling

A literature review of the physics and modelling of water-in-oil emulsification is presented. The understanding of the physics of emulsion formation is still incomplete, but developing. The formation of emulsions is due to the surfactant-like action of polar compounds (resins) and asphaltenes in oil. These compounds act to maintain small (1–20 μm) droplets of water in oil. Volatile aromatic compounds in crude oils solubilize asphaltenes and resins. Crude oils containing lower quantities of these volatile compounds or BTEX (benzene, toluene, ethylbenzene, xylenes) will form emulsions given sufficient turbulent sea energy. Oils may lose the BTEX component by weathering before being capable of forming stable emulsions. The kinetics and energy of formation of emulsions is not well understood. Emulsions are often reported to form rapidly after the necessary chemical conditions are achieved and where there is significant wave action or other turbulent energy. Oil spill models generally employ a first-order rate law (exponential) to predict emulsion formation.     

Looking to the Future––Setting the Agenda for Oil Spill Prevention,Preparedness and Response in the 21st Century

The Oil Pollution Act of 1990 (OPA 90) was largely driven by the catastrophic EXXON VALDEZ tanker spill and several other major tanker spills that followed in 1989. Under the OPA 90 mandate, the US Coast Guard, in partnership with other Federal agencies and industry have implemented a number of initiatives that have significantly enhanced the national oil spill prevention, preparedness and response capability. Declining trends in the volume of oil spilled into US waters indicates that these initiatives are at least in some measure successful.The Coast Guard is now concerned about what the future may hold in terms of oil pollution threats, and prevention, preparedness and response program shortcomings and opportunities in the future. To address this issue, the Coast Guard, in partnership with other National Response Team agencies and industry, is conducting a Broad-Based Programmatic Risk Assessment to develop a comprehensive vision and strategy for the Oil Spill Prevention, Preparedness and Response (OSPPR) Program in the 21st Century. This study will characterize the current and emerging oil spill threats by source category, assess the potential impacts of these threats to define overall risk, and examine the current and projected effectiveness of OSPPR initiatives in minimizing these risks. Key issues, problems and focus areas will be identified and targeted for follow-on risk analysis and management activities by the Coast Guard and agency and industry stakeholders.     

COASTMAP: An integrated monitoring and modeling system to support oil spill response

One of the most difficult tasks in oil spill response modeling is to provide accurate estimates of the currents and winds during the spill event. This is typically done in an ad-hoc, subjective manner combining very limited field observations with simplified hydrodynamic and meteorological models. As an alternative an integrated environmental monitoring and modeling system, called COASTMAP, is presented. COASTMAP allows the user to collect, manipulate, display, and archive real-time environmental data through an embedded geographic information system and environmental data management tools; to perform simulations with a suite of environmental models (e.g. hydrodynamics, meteorological) in order to predict dynamics in the operational area and to assimilate real-time data into the models to allow hindcasting, nowcasting and forecasting. COASTMAP, operational on a personal computer, is controlled by mouse/keyboard through a series of menus and uses color graphics to present model predictions (plots, graphs, animations) and the results of data analyses. The software is designed using a shell based architecture making application to any geographic location simple and straightforward.In the present paper, COASTMAP is linked with OILMAP to provide a fully operational, real-time system that allows prediction of circulation, winds and oil spill trajectory and fate for estuarine and coastal sea areas. System performance is illustrated by the simulation of the trajectory of oil tracking buoys during two experiments performed in the lower west passage of Narragansett Bay. Simulation results using several forecast procedures, with/without real-time data, are presented.     

Summary of Development and Field Testing of the Transrec Oil Recovery System

This paper summarizes the development, field testing and performance evaluation of the Transrec oil recovery system including the Framo NOFO Transrec 350 skimmer and multi-functional oil spill prevention and response equipment and presents performance data, not published before, from full-scale experimental oil spills in the North Sea from 1981 to 1990. The rare data provides useful information for evaluation of mechanical clean-up capabilities and efficiency, in particular, for responders who are using this equipment in many countries around the world.The development of the Transrec oil recovery system represents one of the most comprehensive efforts funded to date by the oil industry in Norway to improve marine and open ocean oil spill response capabilities. The need for improvements was based upon early practical user experience with different oil recovery systems, and test results from experimental oil spills in the North Sea.The result of the development efforts increased: (1) skimmer efficiency from approximately 15–75% (it reached 100% under favorable environmental conditions); (2) oil emulsion recovery rate from approximately 20–300 m³/h; (3) recovery system efficiency from approximately 15–85% in 1.5 m significant wave height; (4) oil emulsion thickness from approximately 15–35 cm; (5) weather-window for mechanical recovery operations from 1.5 to 3.0 m significant wave height; (6) capability for transfer of recovered oil residue to shuttle tankers in up to 4 m significant wave height and 45 knot winds; (7) capability for operations at night.The new Transrec oil recovery system with the special J-configuration virtually eliminated skimming operation downtime, and damage to booms and equipment failures that had been caused by oil spill response vessel (OSRV) problems with maintaining skimming position in the previous three-vessel oil recovery system with the boom towed in U-configuration. The time required to outfit OSRVs dropped from approximately 30–<1 h, reducing time from notification to operation on site by more than 24 h.Improvement in oil recovery resulted in the acceptance of a new oil spill preparedness and response plan. The new plan reduced the need for oil recovery systems from 21 to 14, towing vessels in preparedness from 42 to 18, and personnel on stand-by from 135 to 70, which subsequently reduced the total contingency and operational costs by almost 50%. These cost reductions resulted from lower contingency fees for personnel, fewer towing vessels on stand-by, less expensive open ocean training and exercises, less equipment and reduced storage space to lease, and simplified equipment maintenance.     

Modeling the fate of oil spills at sea

A numerical model for the simulation of the physicochemical weathering processes of an oil spill at sea is presented based on state-of-the-art models. The model includes the most significant processes: spreading, evaporation, dispersion into the water column, emulsification and the change in viscosity and density. These processes depend on each other and are allowed to vary simultaneously since processes are described by a set of differential equations, solved by a fourth-order Runge-Kutta method. Numerical examples are given, in order to test the results obtained, and compared with available experimental data in the literature. The model predicts well the variation of water incorporation, density and viscosity but seems to overestimate the fraction evaporated. However more experimental data are needed to calibrate and validate the model since differences in the composition of the simulated oil and the samples from which experimental data are taken may occur in evaporation studies. The model is suitable to join other modules for the prediction of the spill trajectory by advection due to winds and currents and sub-sea transport.