Environmental Statement - Maersk Oil

5.1.3. PHYSICAL PRESENCE
5‐ 6
Balloch Field Development Environmental Statement
Section 5 Assessment of Potential Impacts and Controls
This section discusses the potential environmental impacts associated with the physical presence of
the drilling rig and associated vessels, as well as the drilling rig’s anchors and chains.
Rig and associated vessels
The presence of a drilling rig and the increase in associated vessel movements has potential
implications for other sea users, notably those involved in commercial fishing and shipping.
Once in position, the drilling rig will have a temporary 500 m exclusion zone around it meaning that
there will be no fishing or unauthorised vessels within that area. While the drilling rig is on station the
GPIII’s guard vessel will serve the standby requirements of the drilling rig, thus minimising vessel use.
Total fishing effort within the area of the development is approximately 1 % of total UK effort
(Scottish Government, 2012). Shipping activity in the area is also considered to be moderate (DECC,
2012). With mitigation measures in place, there are not expected to be any interactions between the
rig and its associated support vessels and other vessels.
Drilling rig anchors and chains
The drilling rig will be held in place by an anchor mooring spread consisting of a maximum of 12
anchors. The precise arrangement of the anchors around the rig will be defined by a mooring analysis
which will be undertaken prior to bringing the rig into the field. This will take account of the water
depth, tidal and other currents, prevailing wind conditions and any seabed features at the well
location. Each anchor weighs approximately 12 te and will produce a linear scar of approximately
50 m length during setting, before sinking into the seabed. The depth of penetration will be
dependent on the shear strength and load bearing capacity of the seabed soils.
Effects and their duration on the benthic community structure from disturbance caused by the
anchors are related to individual species biology. As the majority of benthic species recorded on the
European continental shelf have short life spans and relatively high reproduction rates, the effect of
the anchors on the local benthic community is likely to be low.
Proposed control measures for impacts associated with physical presence during the drilling phase
Control measures in place to mitigate impacts from the physical presence of the drilling rig and
associated vessels are presented below.
In consideration of the control measures detailed above, the physical presence of the drilling rig and
associated support vessels has been assessed as having a low/negligible impact.
5.1.4. NOISE: DRILLING
The impacts from noise generated by the support vessels and drilling rig are discussed in Section 5.4.
5.2. INSTALLATION PHASE
Proposed Control Measures
An exclusion zone will be established around the drilling rig, enforced by a standby vessel.
Mooring analysis will determine rig anchor position.
This section discusses the impacts associated with the installation of the subsea infrastructure.
Emissions produced during subsea installation are primarily associated with vessel use. Subsea
installation activities will cause disturbance to the seabed and could potentially interfere with other
users of the sea. Underwater noise associated with the installation vessels and piling of the cooling
spools is assessed in Section 5.4. This section considers the emissions to air produced by the vessels,
physical presence of the subsea infrastructure, discharges associated with hydrotesting and the noise
associated with piling of the manifold.