The Davis Strait - DCE - Nationalt Center for Miljø og Energi

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(wells and pipelines) and to discharges to sea and emissions to air. The major
discharge to the sea is produced water.
2.7 Produced water
Produced water is by far the largest ‘by-product’ of the production process.
On a daily basis some Canadian offshore fields produced between 11,000
and 30,000 m 3 /day (Fraser et al. 2006), and the total amount produced on the
Norwegian shelf was 174 millions m 3 in 2004 (OLF 2005). Produced water
contains small amounts of oil, salts from the reservoir and chemicals added
during the production process. Some of these chemicals are acutely toxic, or
are radioactive, contain heavy metals, have hormone disruptive effects or act
as nutrients which influence primary production (Lee et al. 2005). Some are
persistent and have the potential to bio-accumulate. The produced water
moreover contributes to the major part of the oil pollution during normal
operations, e.g. in Norway up to 88 %.
Produced water has usually been discharged to the sea after a cleaning process
which reduces the amount of oil to levels accepted by the authorities (in
the North Sea sector of Norway, for example, 40 mg/l or 30 mg/l as recommended
by OSPAR). Discharges of produced water and chemicals to the water
column appear to have acute effects on marine life only in the immediate
vicinity of the installations due to the dilution effect. But long-term effects of
the releases of produced water have not been studied, and several uncertainties
have been expressed concerning, for example, the hormone-disrupting
alkylphenols and radioactive components with respect to toxic concentrations,
bioaccumulation, etc. (Meier et al. 2002, Rye et al. 2003, Armsworthy et
al. 2005).
Due to environmental concerns in the Arctic environment, discharges will be
further reduced, e.g. by the discharge policy in the Lofoten-Barents Sea area
(Anon 2003b), where produced water will be re-injected except during a 5 %
‘off-normal’ operation time (Anon 2003b).
2.8 Air emmissions
Emissions to the air occur during all phases of petroleum development, including
seismic survey and exploration drilling, although the major releases
occur during development and production. Emissions to air are mainly
combustion gases from the energy producing machinery (for drilling, production,
pumping, transport, etc.). For example, the drilling of a well may
produce 5 million m 3 exhaust per day (LGL 2005). But also flaring of gas and
trans-shipment of produced oil contribute to emissions. The emissions consist
mainly of greenhouse gasses (CO2, CH4), NOx, VOC and SO2. The production
activities produce large amounts of CO2 in particular, and, for example,
the emission of CO2 from a large Norwegian field (Statfjord) was
more than 1.5 million tonnes in 1999 (STF 2000), and the drilling of the three
exploration wells in 2010 in the Disko West area resulted in the emission of
105,000 tonnes of CO2.
Another very active greenhouse gas is methane (CH4), which is released in
small amounts together with other VOCs from produced oil during transshipment.