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

een eliminated on the grounds of environmental concerns. OBMs may be
used for special drillings, but then the mud is injected into wellbores or
brought to land for treatment.
The general pattern of impacts on benthic animals from cuttings from Norwegian
wells is that OBM cuttings elicit the most widespread impacts and
WBM cuttings the least. Ester-based cuttings have been shown to cause severe
but short-lived effects due to their rapid degradation, which may result
in oxygen depletion in the sediments. Olefin-based cuttings are also degraded
fairly rapidly, but without causing oxygen deficiency and therefore have
short-lived and moderate effects on the fauna.
Most of the impact studies on mud and drill cuttings are made with OBMs
(e.g., Davies et al. 1984, Neff 1987, Gray et al. 1990, Ray & Engelhardt 1992,
Olsgaard & Gray 1995, Breuer et al. 2004). Effects from OBMs were widespread
(up to 6 km from the release site) and persisted longer than the release
phase. Furthermore, the area affected continued to increase in size for
several years after discharge ceased (Breuer et al. 2008) and sublethal effects
in some species of fish living near drill sites were also detected (Davies et al.
1984). A further risk from discarding cuttings polluted with oil residues is
tainting of commercial fish (see Section 11.2.6).
Synthetic mud also leads to impacts on benthic fauna, though less pronounced
than around platforms where OBMs were used (Jensen et al. 1999).
Field studies on impacts from WBMs are relatively few. A few specially designed
surveys indicated that effects are restricted to a distance of less than
100 m from the platforms (Schaaning et al. 2008 and references therein). The
use of WBM combined with cleaning of the cuttings may therefore limit the
effects on the benthos to highly localised areas around each exploration drill
site (Table 10.1.2). The use of WBM potentially moves effects on the seafloor
to the water column, where dilution is a major factor in reducing impacts. In
Norway a change to WBM has resulted in a marked decrease of the level of
impacts on the seafloor (Renaud et al. 2007).
Cold water corals and sponges are also sensitive to suspended material in
the water column (Table 10.1.2) (Freiwald et al. 2004, SFT 2008). Corals have
been found in the western part of the Davis Strait (Edinger et al. 2007) and in
Greenland waters they are frequently encountered along the continental
slope of Southwest Greenland, including the assessment area (ICES 2010a).
Recently, a ban against trawling in two areas south of Maniitsoq (64°N) was
suggested due to observations of high abundance of corals. As the seabed at
all potential drill sites is surveyed for these organisms before drilling, it
should be possible to avoid impacts on this sensitive biota in Greenlandic
waters.
Multiple drillings carried out when a field is developed may cause more
widespread effects on the benthos and it is important to note in this regard
that the seafloor fauna in the assessment area is still poorly known. Discharges
of cuttings with water-based drill fluids are likely to disperse widely
in the water column before reaching the seabed and may also impact pelagic
organisms such as plankton (Røe & Johnsen 1999, Jensen et al. 2006). However,
more knowledge is needed on the hydrodynamics to evaluate the
spreading, dilution and sedimentation of the substances. Biological effects
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