RESUMEN
An earlier paper demonstrated a methodology for modeling the spreading process with a Gaussian random walk procedure, but was limited to the gravity-viscous spreading regime. Here we extend the methodology of representing spread and transport of oil slicks on calm sea surface by updated Voronoi diagrams to account for the surface tension-viscous spreading regime as well. We have utilized the analogy between diffusion and spreading processes by defining a step length for the particle-based random walk scheme. In this study, calculation of the diffusive length is improved by including the surface tension term in the numerical solution method. The results from the numerical simulation of the spreading oil slick agree very well with the analytical solutions. The solution is robust in that good agreement is achieved for a large range of model and numerical solution parameters. This modeling procedure remains valid only for passive, quiescent spreading. The inclusion of spreading due to important horizontal and vertical turbulent shear processes in the Voronoi diagram paradigm remains a challenge for future work.
Asunto(s)
Gravitación , Difusión , Predicción , Tensión Superficial , ViscosidadRESUMEN
Adverse impacts of drilling discharges on marine benthic environments have been observed since the advent of offshore drilling operations for exploration and production of oil and gas. This study utilizes a marine sediment model based on a system of equations that has been developed earlier to assess environmental impacts of drilling waste discharges. Bioturbation, bio-degradation and natural burial processes are included in the model. The model is based on the diagenetic equations, providing vertical concentration profiles of dissolved oxygen, naturally deposited substances and discharged substances in the marine sediment as a basis for marine risk assessment. The governing equations are solved by a random walk particle-tracking method for each constituent evaluated explicitly in time. The developed model is enhanced with a kernel smoothing method to obtain smooth concentration profiles. Simulation results reveal that the method demonstrates stable behavior for different model parameters, providing a promising alternative to finite difference approaches.
Asunto(s)
Sedimentos Geológicos/química , Modelos Teóricos , Industria del Petróleo y Gas , Ambiente , Sedimentos Geológicos/análisis , Distribución Aleatoria , Medición de Riesgo/métodosRESUMEN
We introduce a methodology for representation of a surface oil slick using a Voronoi diagram updated at each time step. The Voronoi cells scale the Gaussian random walk procedure representing the spreading process by individual particle stepping. The step length of stochastically moving particles is based on a theoretical model of the spreading process, establishing a relationship between the step length of diffusive spreading and the thickness of the slick at the particle locations. The Voronoi tessellation provides the areal extent of the slick particles and in turn the thicknesses of the slick and the diffusive-type spreading length for all particles. The algorithm successfully simulates the spreading process and results show very good agreement with the analytical solution. Moreover, the results are robust for a wide range of values for computational time step and total number of particles.
Asunto(s)
Modelos Teóricos , Contaminación por Petróleo/análisis , Contaminantes Químicos del Agua/análisis , AlgoritmosRESUMEN
Drilling discharges are complex mixtures of base-fluids, chemicals and particulates, and may, after discharge to the marine environment, result in adverse effects on benthic communities. A numerical model was developed to estimate the fate of drilling discharges in the marine environment, and associated environmental risks. Environmental risk from deposited drilling waste in marine sediments is generally caused by four types of stressors: oxygen depletion, toxicity, burial and change of grain size. In order to properly model these stressors, natural burial, biodegradation and bioturbation processes were also included. Diagenetic equations provide the basis for quantifying environmental risk. These equations are solved numerically by an implicit-central differencing scheme. The sediment model described here is, together with a fate and risk model focusing on the water column, implemented in the DREAM and OSCAR models, both available within the Marine Environmental Modeling Workbench (MEMW) at SINTEF in Trondheim, Norway.
Asunto(s)
Ambiente , Industria Procesadora y de Extracción , Sedimentos Geológicos/análisis , Medición de Riesgo/métodos , Ecotoxicología/métodos , Modelos Teóricos , Noruega , Océanos y MaresRESUMEN
Drilling discharges are complex mixtures of chemical components and particles which might lead to toxic and nontoxic stress in the environment. In order to be able to evaluate the potential environmental consequences of such discharges in the water column and in sediments, a numerical model was developed. The model includes water column stratification, ocean currents and turbulence, natural burial, bioturbation, and biodegradation of organic matter in the sediment. Accounting for these processes, the fate of the discharge is modeled for the water column, including near-field mixing and plume motion, far-field mixing, and transport. The fate of the discharge is also modeled for the sediment, including sea floor deposition, and mixing due to bioturbation. Formulas are provided for the calculation of suspended matter and chemical concentrations in the water column, and burial, change in grain size, oxygen depletion, and chemical concentrations in the sediment. The model is fully 3-dimensional and time dependent. It uses a Lagrangian approach for the water column based on moving particles that represent the properties of the release and an Eulerian approach for the sediment based on calculation of the properties of matter in a grid. The model will be used to calculate the environmental risk, both in the water column and in sediments, from drilling discharges. It can serve as a tool to define risk mitigating measures, and as such it provides guidance towards the "zero harm" goal.