Computer Simulation of Offshore Oil Spill Cleanup Operations

Abstract

ABSRACT Computer simulation provides a powerful tool for use in selection and design of oil spill control equipment. This paper describes an oil spill simulation program which enables the user to assess the effects of weather and of the performance characteristics of oil spill control equipment on the recovery of spilled oil. Results of a sample case are shown which indicate the trends which might be expected from variations in the number of skimmers used, their ability to operate to different maximum wave heights, other skimmer performance characteristics, length of time spent on the job, and size of the spill. INTRODUCTION Anyone faced with purchase of oil spill control equipment has a serious problem: How much of what type of equipment is needed? Until recently, there has been no logical answer to this problem. Purchase of oil spill control equipment has, at best, been based on educated guesses. The purpose of this paper is to present a better method by which we can select equipment for oil spill containment and recovery. The performance of oil spill control equipment in calm water is easy to assess. However, the performance generally deteriorates as the weather becomes more severe. If the weather becomes very severe, it may be necessary to shut down operations or to seek shelter. The most important weather variable which affects the performance of oil spill skimmers and booms is the wave height; we can usually determine a characteristic wave height above which a given skimmer cannot operate. Similarly, the maximum wave height above which a given boom will not contain oil can be determined. Thus, we can characterize the performance of oil spill control equipment in terms of wave height. Historical (statistical) weather data for any given offshore location can usually be obtained. These data can be used to generate realistic synthetic weather synopses, using the theory of Markov chains.1,2 In turn, the weather synopses can be used to deduce corresponding oil spill recovery synopses, using a computer simulation program we have developed.3 In any run, using the oil spill simulation program, the computer keeps track on the weather, which can affect not only the ability of skimmers to recover oil or booms to retain spilled oil but also the ability of equipment to mobilize and leave shelter for the job site. The program also keeps track of the spreading of oil on water and (if desired) evaporation of the lighter components, and from this information the computer deduces the area1 extent of the oil spill and the resulting average oil thickness. This information is needed because the recovery efficiency (oil: water ratio) of any skimmer depends on the oil thickness. Booms or surface tension modifiers can be used to contain the spilled oil. The end result of the computations in any single computer run is the amount of oil recovered in that run. For our simulations, we usually generate 100 different weather synopses (thereby giving a statistical distribution of weather simulations) and compute the oil recovery for each.