IAHR, founded in 1935, is a worldwide independent member-based organisation of engineers and water specialists working in fields related to the hydro-environmental sciences and their practical application. Activities range from river and maritime hydraulics to water resources development and eco-hydraulics, through to ice engineering, hydroinformatics, and hydraulic machinery.
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You are here : eLibrary : IAHR World Congress Proceedings : 36th Congress - The Hague (2015) ALL CONTENT : Special sessions : How many runs should we run? Ęc stochastic oil spill modelling for environmental impact assessment o...
How many runs should we run? Ęc stochastic oil spill modelling for environmental impact assessment over large operational areas
Quantifying the potential exposure from hypothetical oil spill scenarios is critical for preparing environmental impact
assessments (EIA), emergency contingency response plans and financial risk analysis for oil and gas operations in
offshore waters. Stochastic oil spill trajectory and fate modelling has become the industry standard and best practice for
assessing risks of exposure. This intensive approach involves running numerous simulations to track the trajectory and
fate of oil at sea due to variable metocean conditions, with the aim of accounting for the natural variability of conditions in a
study region. This allows the determination of, for example, the zone of potential impact (ZPI) and probability statistics for
risk assessment. Such approach is based on the assumption that the specific location where a spill scenario may occur is
clearly defined, which is the case of some operations e.g. a drilling of a well or operations at a specific site. However,
several oil and gas related operations involve large operational areas instead of a single location, e.g. seismic surveys,
laying of pipelines on the seafloor, shipment of hydrocarbons, etc. Adaptation of the conventional, single location,
approach is required to achieve comprehensive assessment of those cases where a spill event could potentially occur
anywhere within an operational area. Basic practical questions in this regard arise, such as: how many potential spill
locations and simulations are required for assessments over large operational areas? Here we present a conceptual
framework to contribute to answering these questions. The framework is inspired on the concept of species-area curve
from ecological sciences, which relates the number of species found within certain environments to the size of its area.
This framework was tested for a hypothetical case study, with 1,000 stochastic oil spill simulations completed at randomly
selected sites within an operational area of approximately 8,000 km2. The simulation outputs were analysed to calculate
the area of the ZPI at a series of threshold concentrations of oil floating on the surface and entrained in the water column.
The cumulative results aggregated for successive sets of 100 simulations indicated that the ZPI area increased, as more
simulations were included in the assessment. However, the relationship between ZPI area and number of simulations
tended to be asymptotic; resembling the species-area curve. For the case study tested, 80% and 95% of the predicted ZPI
area were reached when including 600 and 900 simulations, respectively. A detailed description of the procedure and
insights gained during the assessment are presented herein, with the aim of contributing towards better representation of
the risks when considering exploration and development of our ocean resources.
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Chapter : IAHR World Congress Proceedings
Category : 36th Congress - The Hague (2015) ALL CONTENT
Article : Special sessions
Date Published : 28/08/2015
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