Alun Lewis

Oil spill modeling towards the close of the 20th century: overview of the State of the Art

Abstract The state-of-the-art in oil spill modeling is summarized, focusing primarily on the years from 1990 to the present. All models seek to describe the key physical and chemical processes that transport and weather the oil on and in the sea. Current insights into the mechanisms of these processes and the availability of algorithms for describing and predicting process rates are discussed. Advances are noted in the areas of advection, spreading, evaporation, dispersion, emulsification, and interactions with ice and shorelines. Knowledge of the relationship between oil properties, and oil weathering and fate, and the development of models for the evaluation of oil spill response strategies are summarized. Specific models are used as examples where appropriate. Future directions in these and other areas are indicated

Oil and water separation in marine oil spill clean-up operations

Abstract This paper discusses the changes in spilled oil properties over time and how these changes affect differential density separation. It presents methods to improve differential density, and operational effectiveness when oil-water separation is incorporated in a recovery system. Separators function because of the difference in density between oil and seawater. As an oil weathers this difference decreases, because the oil density increases as the lighter components evaporate. The density also increases as the oil incorporates water droplets to form a water-in-oil emulsion. These changes occur simultaneously during weathering and reduce the effectiveness of separators. Today, the state-of-the-art technologies have limited capabilities for separating spilled marine oil that has weathered. For separation of emulsified water in an emulsion, the viscosity of the oil will have a significant impact on drag forces, reducing the effect of gravity or centrifugal separation. Since water content in an emulsion greatly increases the clean up volume (which can contain as much as two to five times as much water as the volume of recovered oil), it is equally important to remove water from an emulsion as to remove free water recovered owing to low skimmer effectiveness. Removal of both free water and water from an emulsion, has the potential to increase effective skimming time, recovery effectiveness and capacity, and facilitate waste handling and disposal. Therefore, effective oil and water separation in marine oil spill clean-up operations may be a more critical process than credited because it can mean that fewer resources are needed to clean up an oil spill with subsequent effects on capital investment and basic stand-by and operating costs for a spill response organization. A large increase in continuous skimming time and recovery has been demonstrated for total water (free and emulsified water) separation. Assuming a 200 m3 storage tank, 100 m3 h−1 skimmer capacity, 25% skimmer effectiveness, and 80% water content in the emulsion, the time of continuous operation (before discharge of oil residue is needed), increases from 2 to 40 h and recovery of oil residue from 10 to 200 m3. Use of emulsion breakers to enhance and accelerate the separation process may, in some cases, be a rapid and cost effective method to separate crude oil emulsions. Decrease of water content in an emulsion, by heating or use of emulsion breakers and subsequent reduction in viscosity, may improve pumpability, reduce transfer and discharge time, and can reduce oily waste handling, and disposal costs by a factor of 10. However, effective use of emulsion breakers is dependant on the effectiveness of the product, oil properties, application methods and time of application after a spill.

Oil Spill Dispersants

Introduction: The purpose of any oil spill response is to minimise the damage that could be caused by the spill. Dispersants are one of the limited number of practical responses that are available to respond to oil spills at sea. When oil is spilled at sea, a small proportion will be naturally dispersed by the mixing action caused by waves. This process can be slow and proceed to only a limited extent for most situations. Dispersants are used to accelerate the removal of oil from the surface of the sea by greatly enhancing the rate of natural dispersion of oil and thus prevent it from coming ashore. Dispersed oil will also be more rapidly biodegraded by naturally occurring microorganisms. The rationale for dispersant use is that dispersed oil is likely to have less overall environmental impact than oil that persists on the surface of the sea, drifts and eventually contaminates the shoreline. The development of modern dispersants began after the Torrey Canyon oil spill in 1967. Many lessons have been learned since that spill, and consequently the modern dispersants and application techniques in use today have become an effective way of responding to an oil spill. For example, the dispersant response to the Sea Empress spill in 1996 demonstrated that dispersants can be very effective and prevent a much greater amount of environmental damage from being caused (6). This chapter describes the chemistry and physics of dispersants, planning and decision-making considerations, and finally their practical application and operational use in oil spill response.

Norwegian Testing of Emulsion Properties at Sea--The Importance of Oil Type and Release Conditions

This paper is a review of the major findings from laboratory studies and field trials conducted in Norway in recent years on the emulsification of oils spilled at sea. Controlled bench-scale and meso-scale basin experiments using a wide spectrum of oils have revealed that both the physico-chemical properties of the oils and the release conditions are fundamental determinants of the rate of emulsion formation, for the rheological properties of the emulsion formed and for the rate of natural dispersion at sea. During the last decade, several series of full-scale field trials with experimental releases of various crude oils have been undertaken in the North Sea and the Norwegian Sea. These have involved both sea surface releases, underwater pipeline leak simulations (release of oil under low pressure and no gas) and underwater blowout simulations (pressurized oil with gas) from 100 and 850 m depth. The field trials have been performed in co-operation with NOFO (Norwegian Clean Seas Association for Operating Companies), individual oil companies, the Norwegian Pollution Control Authority (SFT) and Minerals Management Services (MMS). SINTEF has been responsible for the scientific design and monitoring during these field experiments. The main objectives of the trials have been to study the behaviour of different crude oils spilled under various conditions and to identify the operational and logistical factors associated with different countermeasure techniques. The paper gives examples of data obtained on the emulsification of spilled oil during these field experiments. The empirical data generated from the experimental field trials have been invaluable for the validation and development of numerical models at SINTEF for predicting the spreading, weathering and behaviour of oil released under various conditions. These models are extensively used in contingency planning and contingency analysis of spill scenarios and as operational tools during spill situations and combat operations. � 2003 Elsevier Science Ltd. All rights reserved.

Modelling of dispersant application to oil spills in shallow coastal waters

Abstract Application of dispersants in shallow water remains an issue of debate within the spill response community. An experimental oil spill to evaluate potential environmental impacts and benefits of applying dispersants to spills in shallow water has therefore been under consideration. One site being considered was Matagorda Bay, on the Texas coast. Coupled three-dimensional oil spill and hydrodynamic models were used to assist in the design of such an experiment. The purpose of the modeling work was to map hydrocarbon concentration contours in the water column and on the seafloor as a function of time following dispersant application. These results could assist in determining the potential environmental impact of the experiment, as well as guiding the water column sampling activities during the experiment itself. Eight potential experimental oil spill scenarios, each of 10 bbl in volume, were evaluated: 4 release points, each under two alternate wind conditions. All scenarios included application of chemical dispersants to the slick shortly after release. Slick lifetimes were under 5 h. Due to the shallow depths, some fraction (2–7%) of the released hydrocarbons became associated with bottom sediments. The algorithms used for the oil droplet—sediment interactions are theoretical, and have not been verified or tested against experimental data, so the mass balances computed here must be considered tentative. Currents computed by the hydrodynamic model are consistent with previous observations: the circulation is largely tidally driven, especially near the ship channel entrance. In the center of the bay, the circulation appears relatively weak. The use of water column drifters with surface markers during the experiment would augment model results in assisting activities to monitor concentrations. These simulations suggest that the eventual behavior of an oil droplet cloud in the middle of the bay will be relatively insensitive to release point or time in the tidal cycle. A limited analysis was run to evaluate model sensitivity to the oil-sediment sorption coefficient. Increasing this coefficient by a factor of 10 results in an approximately linear increase in the fraction of oil in the sediments. Sensitivity of estimated time-to-zero-volume for the 0.1-ppm concentration contour demonstrated that the model prediction of 3.5 days was associated with an uncertainty of ±12 h for a release of 10 barrels. This time estimate is also a function of the oil-sediment interaction rate, since more oil in the sediments means less oil in the water column.

WEATHERING AND DISPERSION OF NAPHTHENIC, ASPHALTENIC, AND WAXY CRUDE OILS

ABSTRACT The chemical composition and physical properties of a crude oil determine the behavior of the oil and the way its properties will change when the oil is spilled at sea. Reliable knowledge ...

SINTEF/IKU OIL-WEATHERING MODEL: PREDICTING OILS' PROPERTIES AT SEA

ABSTRACT This paper describes the empirical approach used in the development of the IKU oil-weathering model (IKU-OWM). Weathering data from field trials with experimental oil spills during the pas...

WEATHERING AND CHEMICAL DISPERSION OF OIL AT SEA

ABSTRACT Small-scale laboratory methods were used to simulate the weathering processes that occur when crude oil is spilled at sea. Changes caused by evaporation and water-in-oil (w/o) emulsificati...

ASSESSING DISPERSANT EFFECTIVENESS FOR HEAVY FUEL OILS USING SMALL-SCALE LABORATORY TESTS

ABSTRACT Four bench-scale dispersant tests were used to evaluate three dispersants, Corexit 9500, Superdispersant 25 and Agma Super-concentrate DR 379 with an IFO (Intermediate Fuel Oil) 180 and an...

Heat and chemical treatment of mechanically recovered w/o emulsions

Abstract Nearly all crude oils and some heavier refined products form stable water-in-oil (w/o) emulsions when spilled and weathered at sea. Breaking these emulsions and discarding the separated water allow more oil to be recovered and stored by OSRVs (Oil Spill Recovery Vessels) and make the handling of oily waste easier due to viscosity reduction. This study was conducted to determine whether a combination of heat and emulsion breaker is more effective than either technique used alone. The results will be used to prepare guidelines for treatment of w/o emulsions and planning of large-scale tests. A bench-scale laboratory study was carried out using emulsions prepared from different crude oil residues (BCF-17, Alaskan North Slope and Bonny Light) and a Bunker C fuel oil/gas oil blend (IF-80). Tubes containing w/o emulsions, with or without emulsion breaker added, were partially submerged in a water bath at different temperatures to simulate the heating system of the recovered oil tanks onboard the OSRVs. The effectiveness of the emulsion breaking was measured by recording settled water over a 24 h period. The results showed that: • • The stability of a w/o emulsion and its response to heat and emulsion breaker is highly dependent on different characteristics of the oil from which it is formed. • • Stable w/o emulsions that can be slowly broken by heat alone were, in general, broken much more rapidly if emulsion breaker was added in addition to heat. • • The w/o emulsions formed from relatively paraffinic crude oil (e.g. ANS) exhibit faster breaking rates than w/o emulsions formed from crude oils with high asphaltene content, such as BCF-17. • • All w/o emulsions formed from the crude oil residues could be broken by the application of moderate amounts of heat. W/o emulsions produced from Bunker C/Diesel oil blend were not broken at all by relatively high heat inputs (up to 100°C) and required both the addition of heat and emulsion breaker to obtain partially breaking.