Haibo Niu

Application of entropy analysis of in situ droplet-size spectra in evaluation of oil chemical dispersion efficacy.

In situ droplet-size distributions were measured using a laser in situ scattering and transmissiometry (LISST-100X) particle size analyzer during the evaluation of natural and chemical dispersion efficiency of crude oils under different wave and current conditions. An entropy grouping of the in situ dispersed oil droplet-size spectra has classified the multi-modal droplet-size distributions into different groups based on similar droplet-size spectra characteristics within groups and distinction between groups. A generalized linear logistic regression model was fitted to analyze the effects of a number of factors and their interactions on the grouping of oil droplet-size spectra. The grouped results corresponded to the oil dispersion efficiency at different levels. This new method for droplet-size distribution data analysis can have significant implication in field evaluation of natural and chemical dispersion efficiency of oil.

A Method for Assessing Environmental Risks of Oil-Mineral-Aggregate to Benthic Organisms

ABSTRACT Previous studies have shown that Oil-Mineral-Aggregate (OMA) formation enhances the dispersion of marine oil spills, but the potential impacts of settled OMAs on benthic organisms are not well known. A comprehensive numerical approach is proposed here to model the transport of OMAs and assesses their potential risks. The predicted environmental concentrations (PEC) of settled oil in OMAs was calculated using a random walk particle tracking model and the benchmark concentrations (BCs) of individual hydrocarbon groups were computed based on a equilibrium partitioning (EqP) approach. The likely of risks in terms of Hazard Quotient (HQ) were then determined using a Monte Carlo simulation method. HQ for both aliphatic and aromatic hydrocarbon groups were calculated for OMAs formed with two sediments, Mississippi River Delta (MRD) and Standard Reference Material (SRM). Mean total HQs were also determined by a simple sum of individual HQ. The predicted results from a case study based on a spill of 1000 tons of South Louisiana crude oil in the Gulf of St. Lawrence with a water depth of 80 m show that the SRM is unlikely to cause adverse impacts but this may not be the case for MRD. Furthermore, it has been found that the application of chemical dispersant (CD) increased the risks of MRD but it had little effects on SRM.

Ocean Outfall Mapping Using an Autonomous Underwater Vehicle

Ocean outfalls are difficult to observe and the traditional monitoring methods are expensive and can only provide limited information. As an alternative, Autonomous Underwater Vehicles (AUVs) have proved to be an effective tool for outfall mapping. This paper describes an outfall mapping mission by the MUN Explorer AUV off the east coast of Canada. A submerged freshwater outfall with Rhodamine WT dye was discharged into a bay and the MUN Explorer 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 and future work is needed to provide more detailed plume information.

Study of the dispersion/settling of oil-mineral-aggregates using particle tracking model and assessment of their potential risks

A random walk particle tracking model was used to simulate the motions of oil-mineral-aggregates (OMAs) under hydrodynamic conditions involving wave-induced velocities, random velocities due to turbulence, and the settling velocity due to gravity. Wave-induced and settling velocities for OMAs determined from the application of Stokes’s theory and empirical equations derived from experimental data were used in a series of simulations to evaluate the effects of wave characteristics, particle size distribution, and settling/floating velocity on the transport of OMAs formed from two different types of minerals. The study found that the wave effect on advection/diffusion is of secondary importance when compared to tidal currents and turbulence induced velocity. To assess the risk of OMAs to benthic organisms, predicted environmental concentrations (PEC) was compared to the benchmark concentration (BC) derived for eight different hydrocarbon groups. The simulation results indicate that no risk from both aliphatic and aromatic hydrocarbons can be found for the two cases described in this paper with a 1,000 tonnes spill. The study also showed that aromatic hydrocarbons posed more risk than aliphatic hydrocarbons. For both aliphatic and aromatic hydrocarbons, the C9–C12 group posed greater risk than other groups.

A Coupled Model for Simulating the Dispersion of Produced Water in the Marine Environment

This chapter describes a method for simulating the dispersion of produced water in the marine environment. A near field model, PROMISE, has been coupled with the MIKE3 model using the passive offline coupling method. A hypothetical case study has been conducted to evaluate the method and it has been shown that model coupling is critical in accurately simulating the dispersion. A minimum grid size must be maintained in the far field model to introduce the source term from the near field model correctly.

Experimental and Modelling Studies on the Mixing Behavior of Offshore Discharged Produced Water

A probabilistic based steady state model, PROMISE, was developed to predict the mixing behaviors of produced water in the marine environment. The model was also coupled with a MIKE3 model to study the dispersion in non-steady state conditions. Laboratory experiments were conducted in a 58 m towing tank to calibrate the near field model. Field experiments using an Autonomous Underwater Vehicle (AUV) were also performed to test the ability of an AUV in produced water plume mapping.

Transport properties of offshore discharged synthetic based drilling cuttings

The general purpose of the present study was to study the transport properties of offshore discharged drilling cuttings produced with synthetic based drilling fluids (SBFs). The transport mechanisms include flocculation and settling. For this reason, a digital imaging system was developed to observe the time variation of floc size distribution under a variety of combinations of fluid shear, solid concentration, and salinity. The system was also employed to measure the settling velocities of both aggregated flocs and individual drilling cuttings particles of different shapes. The samples used in this study were collected from a production oil well on the east coast of Canada. Thermal treated samples were also used to study the effects of oleophyllic components on the transport properties. From the experiments, it was shown that the untreated cuttings flocculate faster and have much larger steady state median floc diameter than thermal treated cuttings due to the bridge effect of oleophyllic components. For the same cuttings, the steady state median floc diameter and time needed to reach steady state decreased as the fluid shear, solid concentration, and salinity increased. The settling velocity of flocs was found to be a function of both floc diameter and fluid shear. The settling velocity increased as the fluid shear increased. The solid concentration had no distinguishable effects on the settling of flocs in this study. The flocs produced from thermal treated cuttings settled faster than those produced from untreated cuttings. For individual particles with diameters larger than 0.1 mm, the equations of settling velocity were derived for both untreated and thermal treated cuttings particles. It was demonstrated by the experiments that the particle shape significantly affects the settling velocity of thermal treated cuttings particles of this size range, while it has no effects on the untreated cuttings particles. For cuttings with the same density, treated cuttings settles faster than untreated cuttings. Experimental results are presented and discussed in the paper.