bedford institute of oceanography 2001 in review - Région des ...

CROSS CUTTING ISSUESInteractions between Offshore Oil and Gas Operations andthe Marine Environment- Peter Cranford, Shelley Armsworthy, Kenneth Lee, Tim Milligan, Kee Muschenheim (MarineEnvironmental Sciences Division [DFO]), Charles Hannah, John Loder (Ocean Sciences Division [DFO]),Michael Li, Gary Sonnichsen, and Edward King (Geological Survey of Canada – Atlantic [NRCan])Offshore oil and gas operations off the east coast of Canada haveincreased dramatically within the last decade, and are expanding toinclude shallow coastal and deep slope waters (Fig. 1). Environmentalfactors such as ice, waves, currents, and seabed structure and stabilitycan greatly affect these activities. Conversely, there is also the potentialthat some oil and gas activities may impact the environment. DFOand NRCan have an ongoing research program, largely supported bythe federal Program for Energy Research and Development, to studythe potential impacts of discharges into the environment and environmentalfactors that affect oil and gas activities.Potential environmental impacts associated with the exposure ofmarine organisms to low-level operational waste discharges are anongoing concern. Drilling wastes (spent drilling mud and well cuttings)are the primary concern during exploration and developmentoperations, while produced water recovered from the hydrocarbonbearing strata is the highest volume waste generated during production.Produced water may contain elevated concentrations of metals,nutrients, radionuclides, hydrocarbons, and trace amounts of chemicalagents. A multidisciplinary research program has been initiated byDFO to study the environmental pathways, transport rate, and ultimatefate and effects of drilling and production wastes.Figure 1. Map of the eastern Canadian shelf showing areas where licences have been issued for oil and gas explorationand production.36 / BIO-2001 IN REVIEWFlocculation (the adhesion of smaller particles to form large particles)and surface adsorption (the adhesion of small particles to largerparticles and/or droplets) are important processes in the transportof material in the ocean. Laboratory studies of the behaviour of finedrilling waste particles in seawater suggest that flocculation couldresult in the rapid transport of this material to the seafloor. This is incontrast to the previous view that these particles settle too slowly toaccumulate to levels that can impact benthic organisms. While dissolvedcontaminants are expected to rapidly dilute with seawater toharmless levels, potential toxic metals in produced water wereobserved to transform from dissolved to particulate forms that settledrapidly. Studies also showed that buoyant oil droplets in producedwater could sequester particles on their surface. These studies demonstratethe importance of aggregation processes that mediate the rapidtransport of contaminants to both the surface microlayer and theseabed (Fig. 2). New sampling methods have been developed at BIOto study waste dispersion around drilling platforms. Application ofthese technologies has revealed that elevated concentrations ofdrilling wastes occasionally exist on and above the seafloor arounddrilling platforms. However, elevated concentrations appear to betransient (days to months) as the wastes are eventually dispersed bycurrents and waves.Given these new insights into the fate ofwaste discharges, laboratory studies arebeing conducted to assess the potentialimpact on selected marine organisms.Scallops feed on particles in an area immediatelyabove the seafloor, the benthicboundary layer, where wastes can accumulate.Exposure to different drilling wastesshowed that important biological effectscan result at waste levels that are lowerthan previously reported for other speciestested. Observed impacts on growth andreproduction were not caused by wastetoxicity, but resulted from fine waste particlesinterfering with the animals’ ability tofeed. Research is currently in progress toassess the utility of deploying caged scallopsaround drilling platforms to verifylaboratory observations and to monitorimpacts at offshore drilling sites.Laboratory biotests with produced waterfrom the Scotian Shelf showed that the tox-