Per S. Daling

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

Droplet breakup in subsurface oil releases – Part 1: Experimental study of droplet breakup and effectiveness of dispersant injection

Size distribution of oil droplets formed in deep water oil and gas blowouts have strong impact on the fate of the oil in the environment. However, very limited data on droplet distributions from subsurface releases exist. The objective of this study has been to establish a laboratory facility to study droplet size versus release conditions (rates and nozzle diameters), oil properties and injection of dispersants (injection techniques and dispersant types). This paper presents this facility (6 m high, 3 m wide, containing 40 m(3) of sea water) and introductory data. Injection of dispersant lowers the interfacial tension between oil and water and cause a significant reduction in droplet size. Most of this data show a good fit to existing Weber scaling equations. Some interesting deviations due to dispersant treatment are further analyzed and used to develop modified algorithms for predicting droplet sizes in a second paper (Johansen et al., 2013).

Quantitative analysis of alternate oil spill response strategies using OSCAR

Abstract 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.

Characterization of crude oils for environmental purposes

Abstract A new approach for predicting the behaviour of oil spilled on the sea has recently been developed at IKU, Sintef-Group. The approach includes an extensive laboratory investigation of an oils properties when exposed to weathering. Parameters especially tested are the tendency of the oil to form water-in-oil (w/o) emulsion (mousse), and the susceptibility of the w/oemulsion or water-free weathered oil to disperse using oil spill dispersants. The laboratory results are transformed to field conditions in a numerical model which predicts the rate of weathering processes at sea under different weather conditions. The computer system displays graphical chartsfor the development of each property with time, and estimates the ‘time window’ e.g. for effective application of dispersants under a chosen set of sea conditions. The system may represent an important tool, for contingency planning andfor ‘on-scene’ commanders to facilitate decision-making concerning the use of different countermeasure techniques during oil spill combat operations. This approach may form the basis for a standard method for future characterization of the weathering properties of different oil types which may be spilled under a variety of environmental conditions.

Weathering of Oils at Sea: Model/Field Data Comparisons

Abstract The SINTEF Oil Weathering Model (OWM) has been extensively tested with results from full-scale field trials with experimental oil slicks in the Norwegian NOFO Sea trials in 1994 and 1995 and the AEA 1997 trials in UK. The comparisons between oil weathering values predicted by the model and ground-truth obtained from the field trials are presented and discussed. Good laboratory weathering data of the specific oil as input to the model is essential for obtaining reliable weathering predictions. Predictions provided by the SINTEF-OWM enable oil spill personnel to estimate the most appropriate “window of opportunity” for use of chemical dispersants under various spill situations. Pre-spill scenario analysis with the SINTEF Oil Spill Contingency and Response (OSCAR) model system, in which the SINTEF-OWM is one of several components, has become an important part of contingency plans as well as contingency training of oil spill personnel at refineries, oil terminals and offshore installations in Norway.

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.

Depletion and biodegradation of hydrocarbons in dispersions and emulsions of the Macondo 252 oil generated in an oil-on-seawater mesocosm flume basin.

Physically and chemically (Corexit 9500) generated Macondo 252 oil dispersions, or emulsions (no Corexit), were prepared in an oil-on-seawater mesocosm flume basin at 30-32 °C, and studies of oil compound depletion performed for up to 15 days. The use of Corexit 9500 resulted in smaller median droplet size than in a physically generated dispersion. Rapid evaporation of low boiling point oil compounds (C⩽15) appeared in all the experiments. Biodegradation appeared to be an important depletion process for compounds with higher boiling points in the dispersions, but was negligible in the surface emulsions. While n-alkane biodegradation was faster in chemically than in physically dispersed oil no such differences were determined for 3- and 4-ring PAH compounds. In the oil dispersions prepared by Corexit 9500, increased cell concentrations, reduction in bacterial diversity, and a temporary abundance of bacteria containing an alkB gene were associated with oil biodegradation.

Chemical comparison and acute toxicity of water accommodated fraction (WAF) of source and field collected Macondo oils from the Deepwater Horizon spill

Two Source oils and five field collected oil residues from the Deepwater Horizon incident were chemically characterized. Water accommodated fractions (WAFs) of the Source oils and two of the field-weathered oils were prepared to evaluate the impact of natural weathering on the chemical composition and the acute toxicity of the WAFs. Toxicity test species representing different tropic levels were used (the primary producer Skeletonema costatum (algae) and the herbivorous copepod Acartia tonsa). The results suggest that the potential for acute toxicity is higher in WAFs from non-weathered oils than WAFs from the field weathered oils. The Source oils contained a large fraction of soluble and bioavailable components (such as BTEX (benzene, toluene, ethyl benzene, xylenes) and naphthalene), whereas in the surface collected oils these components were depleted by dissolution into the water column as the oil rose to the surface and by evaporative loss after reaching the sea surface.

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.

Emerging CEN methodology for oil spill identification

The objective of the emerging European Committee for Standardization (CEN) methodology is to provide a forensic tool for the identification of waterborne oil by comparing samples from spills with those of suspected sources. The two working groups under the CEN task force BT/TF 120 have produced two draft guidelines that describe the new methodology: part 1—sampling and part 2—analytical methodology and interpretation of results. Two results that can be achieved in forensic oil spill investigation, “identity” and “nonidentity,” depending on whether spill and candidate source samples are “identical” or “nonidentical.” The emerging CEN methodology for oil spill identification is based on a three-level tiered approach, including gas chromatography–flame ionization detection screening of all involved samples (Level 1), gas chromatography–mass spectrometry fingerprinting of selected spill and candidate source samples (Level 2), and correlation of spill and candidate oil samples based on those diagnostic ratios that can be precisely measured and are resistant to weathering effects (Level 3). By statistical treatment of the ratios and an overall assessment of results from all analytical levels, the oil spill identification using this methodology can be concluded with respect to one of four operational and technically defensible terms: positive match, probable match, inconclusive, or nonmatch.