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Canadian Science Advisory Secretariat
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.
. Since 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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