Dispersion of offshore discharged produced water in the marine environment : hydrodynamic modeling and experimental study

Niu, Haibo (2008) Dispersion of offshore discharged produced water in the marine environment : hydrodynamic modeling and experimental study. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

This study has two major components: hydrodynamic modeling and experimental study of the dispersion of produced water in a marine environment. The general objective was to develop a hydrodynamic model that predicts the concentration of produced water and conduct experiments to validate the model. This consisted of seven more specific objectives: (1) developing a steady state model that predicts the near field, intermediate field, and far field mixing process; (2) integrating the wave effects into the steady state model; (3) conducting uncertainty analysis and expanding the model to probabilistic format; (4) conducting laboratory experiments and validating the model; (5) applying the model to a case study dealing with the discharge from an offshore oil platform; (6) coupling the steady state model with a non-steady state model to study the far field time-dependent dispersion; (7) collecting field data using an Autonomous Underwater Vehicle. -- For the objective (1) and (2), a steady state model named PROMISE (PROduced water Mixing In Steady-state Environment) was developed in this study. The model has four major hydrodynamic modules: (1) a Lagrangian based integral type near field model that employs a new entrainment formulation based on extensive laboratory experiments was employed; (2) a wave effects model that considers the effects of both ocean surface waves and internal waves. A new wave effect formulation based on previous experimental and analytical studies was developed; (3) upstream intrusion and downstream control module; and (4) a buoyant spreading and turbulent diffusion model. Unlike previous approaches which treat the buoyant spreading and turbulent dispersion separately, a unified approach that considers both effects simultaneously was used. -- By analysis of the uncertainties associated with modeling parameters, statistical distributions for these parameters were derived. Together with the known uncertainties of the ambient and discharge conditions, the PROMISE model was used in a probabilistic analysis using the Monte Carlo simulation technique. -- To validate the formulation of the PROMISE model, laboratory experimental data from various sources have been collected. The model has been executed under different conditions to compare with these data. While most of the previous experiments were conducted at small scales, relatively large scale laboratory experiments were conducted in this study to further validate the model. -- To test the performance of the model, a hypothetical study has been performed. Two scenarios were tested: one with the effects of waves and the other without. By integrating the hydrodynamic model with a food chain model, a simulation which studies the distribution of Phenol among the food chain components, especially fish, was performed. -- To study the dispersion of produced water under a non-steady state environment, the PROMISE was coupled with a three-dimensional non-steady state model, MIKE 3. While most previous coupling was only one-way coupling, a two-way coupling was adopted in this study. -- To collect field data to validate the hydrodynamic model and test the potential of using an Autonomous Underwater Vehicle (AUV) to map the produced water outfall, two field experiments using the MUN EXPLORER AUV were conducted. A submerged freshwater outfall with Rhodamine WT dye was discharged into the Holyrood Bay and the AUV equipped with a fluorometer was used to measure the dye concentration and the extent of the dispersed plume. The results have shown that the AUV can be effectively used to map the outfall.

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