Research Document - 2002/120

Modelling Oceanic Fates of Oil, Drilling Muds and Produced Water from the Offshore Oil and Gas Industry, with Application to the Queen Charlotte Basin.

By Crawford, W., Cretney, W., Cherniawsky, J., Hannah, C.

Abstract

This manuscript describes the fate of oil, produced water and drilling muds that may be introduced into the ocean by offshore oil exploration and production, and also discusses models of these fates. Oil releases are generally accidental, whereas produced water and drilling muds enter as a normal part of oil exploration and production.

Efforts to model the oceanic fates of contaminants from the offshore oil and gas industry require both generic models and site-specific models. Generic models, which simulate the behaviour of contaminants in the ocean, have been developed over a period of several decades, and include the cumulative knowledge of laboratory and field experiments, theoretical studies, and experience with acute and chronic releases of contaminants, assembled to provide the industry and regulatory agencies with guidelines for safe, environmentally benign operations. Oil spreading on the ocean, oil advection over the ocean by winds, and oil evaporation are examples of such processes.

The role of combining these individual processes into a computer application that will provide reasonable accounting of the risks and impacts of contaminants, is filled by integrated computer models. In the past decade several commercial products have been developed to fill this requirement, along with a few additional products developed by government and non-profit agencies. These integrated models address two issues. First, the contaminant spread and drift through the ocean must be simulated prior to exploration to answer questions such as:

• If contaminant is spilled at a given spot, what shoreline locations are likely to be affected?
• Where might a spill occur that could threaten a particular shoreline location of concern?
• What concentrations of contaminants will likely reach a given spot, through individual releases of large quantities, or smaller volume but more frequent releases?

Second, if hydrocarbon exploration proceeds, integrated models must be available to predict the motion of any contaminant released, to enable clean-up and protection operations.

It is expected that integrated models will be available to provide the means to address issues such as these for release of floating contaminants. In the case of drilling muds and produced water, which might be released into the ocean at reasonably small rates over the entire life of an oil and gas production region, the computer applications may require additional development. All integrated models require site-specific information. Processes such as oil evaporation, spreading, and emulsification depend on features of local oil. Processes such as drift, emulsification, and shoreline adhesion require knowledge of shoreline slope and material, ocean currents, tidal currents, wind and wave regime, usually at each site in the basin, at each season of the year.

Funding was provided until 1996 by the Panel for Energy Research and Development (PERD) and by Fisheries and Oceans Canada to examine the physical oceanography of the Queen Charlotte Basin, with concentration of effort for seasons between late spring and early autumn. These studies provided information on the general oceanographic properties of this region, as presented by Cretney et al. (2003), and began the development of numerical hydrodynamical models of ocean currents for input to the integrated computer models. The faster computers and cheaper memory and disk storage now available will enable the required improvement of these numerical models.

Recommendations

• Successful modelling of sub-lethal impacts of drilling muds and produced water requires an active laboratory program measuring the dose-response relationships for the contaminants of concern and the organisms of interest.
• Integrated models of contaminant fates must be implemented for the Queen Charlotte Basin, and applied to determine risk of contaminant impact on sites within this region. If oil is discovered during exploration, its properties must be determined and input to integrated models of fates of contaminants in this region prior to oil and gas development. These models must include local meteorological, oceanic and shoreline characteristics.
• Several numerical, hydrodynamical, ocean models have been applied to the Queen Charlotte Basin, and evaluated with oceanographic observations. PERD funding for this program ceased in 1996. Faster computers and improved hydrodynamical models have been developed by the international community in the years since the completion of this program, and funding should be provided to apply these improvements to the Queen Charlotte Basin. Upgrades are required to improve imulations of winter currents, tidal currents, bottom currents, rate of exchange of water between basins, penetration of contaminants into inlets, channels and bays, and the potential of oil to sink below surface brackish water and penetrate into inlets below surface.
• Additional observations are required to provide better model simulations of ocean currents and drift. A program to measure winter currents using surface drifters will help determine the penetration of oil-on-surface into inlets. Better measurement of bottom currents will help determine transport of drilling muds away from well heads, and toward unique biological features such as sponge reefs.
• ince completion of the PERD-funded field program in 1996, there have been major interannual changes in seawater properties in the northeast Pacific Ocean that appear to have impacted fish stocks in the Queen Charlotte Basin. Funding should be provided for an ongoing program to determine inter-annual changes in the seawater properties of the Queen Charlotte Basin, and their impact on the ecology and fish stocks. Without such research, it will be difficult to distinguish changes in ecology due to contaminants from changes due to climate variability and change.
• Accurate wind measurements and forecasts are essential for spill prediction and risk assessment. The present array of Canadian Weather Buoys on the Pacific Coast should be considered a minimum number for data input to oil-spill models and for evaluation of regions-at-risk. Canadian Weather Buoys measure winds in mid-strait, and do not provide needed information on near-shore winds that will influence adhesion of oil on the beaches, or into inlets and narrow channels. Real-time winds as measured at Canadian Weather Buoys and forecast winds based on regional, high resolution models must be available to oil spill responders in the event of an oil spill, if hydrocarbon exploration is to take place

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