Abstract The subject of oil pollution of the sea by the offshore industry is topical as a result of recent incidents both in the U.K and overseas. Whilst these incidents have primarily involved crude carriers, it has led to pressure to quantify the risk to the environment from the offshore industry in general. Here a method for the assessment of the frequency and size of oil spills from offshore installations is presented. It relies on previously reported spills to determine spill size frequency previously reported spills to determine spill size frequency information for a range of offshore activities, such as transport by pipeline, drilling and processing. Modification factors are used so local conditions, such as the number of wells drilled, throughput and well depth, can be considered in the assessment of the oil spill risk from a particular installation.
Introduction Environmental risk is a relatively recent concept but is quickly becoming an important consideration in:
drilling and platform design and operation, environmental assessments of new developments and, overall field and sector management.
The principal environmental risk associated with the offshore industry is seen primarily as the risk of oil spills from exploration, production and transportation facilities such as, pipelines or loading buoys although other risks are present both pipelines or loading buoys although other risks are present both chronic and acute. While incidents that lead to a large release of oil occur infrequently, quantification of the environmental risk from offshore activities is an important aspect of risk management.
In quantifying the environmental risk from either a specific installation or a complete offshore area a number of steps are required. These are:
characterise the offshore installation(s) and activities;identify cases which may lead to an oil spill;estimate the frequency of these cases occurring;determine the spill size for each of the cases;determine and model the spill behaviour on the waterand;quantify the impact on the environment.
A number of methods can be employed for each of these steps. For example, to estimate the size and frequency of spills, methods ranging from those used as a part of detailed quantitative risk assessment (QRA) of an offshore platform to those used in the environmental assessment of offshore oil and gas leases in the US. QRA techniques consider spill volumes and frequencies from individual failures of pipework, process vessels and pipelines. The approach used in US environmental assessments relates spills, greater than 1000 barrels from platforms and pipelines, directly to total oil production. platforms and pipelines, directly to total oil production. This paper outlines the analysis of historical spill data to estimate the size and frequency of oil spills from offshore oil and gas developments. The results of the analysis can be used for the assessment of existing and potential developments.
This paper is organised in the following major sections. First, the scope of environmental risk studies and the background for this particular work are outlined. Second, an overview of the method and information required and an analysis of historical reported oil spills is presented. Based on this analysis and the level of activity the frequency and size of oil spills from offshore developments is given.
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