Interactions between Offshore Oil and Gas Operations and the Marine Environment

Offshore oil and gas operations off the east coast of Canada have increased dramatically within the last decade and are expanding to include shallow coastal and deep slope waters. Environmental factors such as ice, waves, currents and seabed structure and stability can greatly affect these activities. Conversely, there is also the potential that some oil and gas activities may impact the environment. DFO and NRCan have an ongoing research program, largely supported by the federal Program for Energy Research and Development, to study the potential impacts of discharges into the environment and seabed factors that may affect oil and gas activities.

An ongoing concern has been the potential environmental impacts associated with the exposure of marine organisms to low-level operational waste discharges. Drilling wastes (spent drilling mud and well cuttings) are the primary concern during exploration and development operations, while produced water recovered from the hydrocarbon bearing strata is the highest volume waste generated during production. Produced water may contain elevated concentrations of metals, nutrients, radionuclides, hydrocarbons, and trace amounts of chemical agents. A multidisciplinary research program has been initiated by DFO to study the environmental pathways, transport rate, and ultimate fate and effects of drilling and production wastes.

Flocculation (the adhesion of smaller particles to form large particles) and surface adsorption (the adhesion of small particles to larger particles and/or droplets) are important processes in the transport of material in the ocean. Laboratory studies of the behaviour of fine drilling waste particles in seawater suggest that flocculation could result in the rapid transport of this material to the seafloor. This is in contrast to the previous view that these particles settle too slowly to accumulate to levels that can impact benthic organisms. While dissolved contaminants are expected to rapidly dilute with seawater to harmless levels, potential toxic metals in produced water were observed to transform from dissolved to particulate forms that settled rapidly. Studies also showed that buoyant oil droplets in produced water could sequester particles on their surface. These studies demonstrate the importance of aggregation processes that mediate the rapid transport of contaminants to both the surface microlayer and the seabed. New sampling methods have been developed at BIO to study waste dispersion around drilling platforms. Application of these technologies has revealed that elevated concentrations of drilling wastes occasionally exist on and above the seafloor around drilling platforms. However, elevated concentrations appear to be transient (days to months) as the wastes are eventually dispersed by currents and waves.

Given these new insights into the fate of waste discharges, laboratory studies are being conducted to assess the potential impact on targeted marine organisms. Scallops feed on particles in the benthic boundary layer, where wastes can accumulate, and exposures to different drilling wastes showed that important biological effects can result at waste levels that are lower than previously reported for other species tested. Observed impacts on growth and reproduction were not caused by waste toxicity, but resulted from fine waste particles interfering with the animals ability to feed. Research is currently in progress to assess the utility of deploying caged scallops around drilling platforms to verify laboratory observations and for monitoring impacts at offshore drilling sites. Laboratory biotests with produced water from the Scotian Shelf showed that the toxicity of produced water was altered as a result of chemical changes that occur following its discharge. Toxicity was associated with both dissolved and particulate fractions. Preliminary studies suggest that chemical components within produced water such as inorganic nutrients and hydrocarbons may stimulate the rates of primary production and/or induce changes in microbial communities in offshore waters.

To determine the potential trajectories and dispersion of operational wastes at drilling sites, the research program has included a quantitative description of the physical environment. Data from current moorings have been used to develop comprehensive three-dimensional circulation models of the eastern Canadian continental shelf. A benthic boundary layer transport model was developed to use information on the currents, the bottom stress and the settling velocity of the drilling mud to calculate the fate of waste discharges. Model predictions have been integrated with results of biological/chemical studies to assess the risk of environmental impacts resulting from offshore oil/gas developments. We have recently improved the model to include computer code from a continental shelf sediment transport model developed by the Geological Survey of Canada Atlantic (GSCA). This has improved predictions of the effects of both currents and waves on the fate of drilling wastes. Recently we have included a simple model of flocculation and break-up processes to allow the settling rate of wastes to adjust to local environmental conditions. Evaluations of the reliability of models is ongoing, including comparisons with industry observations of waste distributions.

Another important environmental concern for offshore oil and gas developments is the presence of seabed geohazards, including difficult foundation conditions (e.g. weak sediment strata, mass failures, shallow gas, faults, and bouldery till), and geologic processes that may alter seabed stability (e.g. sediment transport and erosion, and seabed iceberg scouring). Detailed knowledge of these seabed stability issues and processes is critical to pipeline routing and drilling site selection, safe and cost-effective engineering designs, and the protection of offshore structures and the environment. Geological coring and sampling, geophysical and multibeam surveys, sediment transport measurements, and modeling are used to identify and assess the nature of seabed instabilities and geologic processes which pose constraints to offshore hydrocarbon developments.

To study seabed erosion and sediment transport, cutting-edge instruments (http://agcwww.bio.ns.ca/support/equipment) have been deployed on Sable Island Bank (SIB) to measure flow intensity, seabed scouring, sediment transport, and mobility of small to medium scale bedforms during storms. Instrument deployments have been combined with repetitive sidescan and multibeam surveys to understand the morphology, sediment transport processes and migration of sand ridges. Geological studies have compiled a detailed database of surface and subsurface sediment features on SIB. Past glacial events and related changes in sea-level have given rise to a complex suite of shallow marine sand and clay bodies. Shallow gas is manifest as small pockets or widespread zones, and tend to be concentrated in specific geologic settings. Mass sediment failure events were found to be rare except on the outer slope.

Iceberg scour research has been focused on the northeastern sector of Grand Banks, and a database of almost 6000 scour features (distribution, dimensions and occurrence frequency) has been compiled. A study was conducted to document the seabed effects of scouring icebergs and to provide insights into the processes and rates of scour decay. Nine grounding sites were surveyed using sidescan sonar, sub-bottom profiler, ROV, and towed cameras. These surveys provide case histories for iceberg impacts and form a unique and comprehensive data set.

Research conducted at BIO enhances our ability to address environmental issues expressed by our clients related to offshore oil and gas operations. The knowledge obtained forms the bases for codes, standards and regulations designed to reduce costs to industry while protecting the public, workers, and the environment from the effects of energy related activities.

Anthropogenic impact on the shelf and marine pollution - structure and scale of anthropogenic impact on the marine environment are considered. Marine pollution as the main, most wide spread and most dangerous factor of anthropogenic impact is discussed.

Oil pollution of the sea - oil pollution of the marine environment, including sources and volumes of oil input.

Decommissioning of offshore structures - click here if you want to learn about abandonment options and secondary use of offshore structures. Explosive activities to remove obsolete offshore installations and their impact on marine life are also discussed.

Oil and gas accidents - information on drilling, transportation and storage accidents during the offshore oil and gas activities.

Gas impact on water organisms - gas impact on fish and other marine organisms is considered. Results of field and laboratory studies, including biological consequences of accidental gas blowouts are discussed.

Natural gas in the marine environment - chemical composition and biological impact of natural gas in the sea.

Spilled oil in the sea - fate, transformations and behavior of oil and oil hydrocarbons in the sea during an oil spill.

Waste discharges - sources, types and volumes of waste discharges during the offshore oil and gas activity are discussed. Chemical composition of discharged wastes (drilling muds, drilling cuttings and produced waters) is described. Atmospheric emissions and their impact on the marine environment are considered.

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