| This study has two major components: hydrodynamic modeling and ecological risk assessment (ERA) of produced water discharge. The general objective was to develop a framework for ecological risk-based design of produced water discharge from an offshore platform. A new approach to initial dilution modeling was proposed based on the hypothesis of additive shear and forced entrainment combined with nonlinear regression. A comparison with other available models shows that the proposed model is better in a number of ways: (1) it does not assume that the current has no effect in the buoyancy-dominated near field (BDNF), which other available models do; (2) in the buoyancy-dominated far field (BDFF) region the model has one parameter fewer than a previously available model yet it is no less accurate; (3) in the transition region it gives a unique solution which the asymptotic models do not; (4) unlike the previous models, the proposed model has approximately the same precision for all regions, i.e. the BDNF, the BDFF, and the transition; and (5) the proposed model can also be presented in a probabilistic form that permits calculation of failure probability for specified model inputs and a threshold dilution.; Hydrodynamic modeling was carved out by integrating near and far field models. A comparison using a case study showed that the proposed hydrodynamic model and the Cornell Mixing Zone Expert System model are generally in good agreement, particularly in estimating average effluent concentrations. However, the proposed model also provides the concentration field in the X-Y directions so that it may be applicable for analysis of mixing zones, which in some cases is defined in terms of the horizontal area around the discharge location. The proposed model can also be readily used in a probabilistic analysis to take into account the uncertainty associated with the model inputs, model coefficients and error term.; The framework was presented systematically using a case study by evaluating design scenarios of produced water discharge relevant to an offshore oil production platform, the Terra Nova oil field, located on the Grand Banks, southeast of St. John's, Newfoundland; Canada. Emphasis of the case study is to show how the risk-based design of produced water discharge could be undertaken. (Abstract shortened by UMI.)... |
