Environmental statement - Flyndre and Cawdor - Maersk Oil

Flyndre and Cawdor Environmental Statement
Section 5 Assessment of Potential Impacts and Control Measures
Vessel type
Total fuel
used (te)
Emissions
CO2 NOx N2O SO2 CO CH4 VOC
Survey vessel 440 1408 26.1 0.10 1.8 6.9 0.8 0.88
DP reel‐lay vessel 575 1840 34.2 0.13 2.3 9.0 0.10 1.15
Trenching support vessel 680 2176 40.4 0.15 2.7 10.7 0.12 1.36
Diving support vessel 1350 4320 80.2 0.30 5.4 21.16 0.24 2.7
Rock placement vessel 150 480 9.0 0.03 0.6 2.4 0.03 0.3
Guard vessel 200 640 11.9 0.04 0.8 3.1 0.04 0.4
Supply vessel 200 640 11.9 0.04 0.8 3.1 0.04 0.4
Total from installation 3,595 11,504 213.7 0.79 14.4 56.36 1.37 7.19
Total from drilling vessels
(Table 5‐3) 6,950 22,246 412.6 1.53 27.83 109.1 1.25 13.9
Total from all vessels
10,545 33,750 626.3 2.32 42.23 165.46 2.62 21.09
2008 UK domestic
shipping emissions 1
‐ 5,400,000 ‐ ‐ ‐ ‐ ‐ ‐
% of UK total ‐ 0.62 ‐ ‐ ‐ ‐ ‐ ‐
1
Source; Department for Transport, 2010.
Note: Atmospheric emissions have been calculated using emission factors from the EEMS Atmospheric
Calculations Issue 1.810a (Austin, 2008).
Table 5‐5 Vessel emissions associated with installation infrastructure.
From Table 5‐5 it can be seen that in the worst case scenario the vessel emissions associated with
drilling of the three wells and installation of the infrastructure amounts to 0.62% of CO2 generated by
UK domestic shipping emissions in 2008.
5.2.2. PHYSICAL PRESENCE
VESSEL ANCHORS
A Dynamically Positioned (DP) reel‐lay vessel will be used to lay the pipelines and hence no anchor
damage to the seabed will be associated with this vessel. However other vessels associated with
laying the infrastructure may hold their position with the use of anchors and a wire mooring spread.
Anchors and anchor spreads can interact with other infrastructure in the marine environment for
example pipelines and cables. However, the risk of interaction between anchor spreads and subsea
infrastructure occurring can be minimised by careful laying of the anchor spread to avoid existing
infrastructure.
As each anchor is laid the depth of anchor penetration will be dependent on the shear strength and
load bearing capacity of the seabed soils; a firm seabed will result in less depth of penetration than a
soft seabed.
A small area of the seabed where each anchor is placed will be compressed as the anchors sink into
the soft seabed, and further disturbance and re‐suspension will occur again as the anchors are
retrieved. Anchor placement can cause mortality or displacement of benthic species in the
immediate area surrounding the disturbed sediment, and a direct loss of habitat and mortality of
sessile seabed organisms that cannot move away from the contact area. Additionally, when the
anchors are removed there is the potential for scars/mounds to be left on the seabed. The seabed is
soft, and damage caused from any anchors are expected to be visible for a number of years. Anchor
scars are formed from the deployment and recovery of anchors in sedimentary areas, particularly
where clay is present immediately beneath the seabed. Although the predominant seabed sediments
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