Environmental statement - Flyndre and Cawdor - Maersk Oil

Flyndre and Cawdor Environmental Statement
Section 5 Assessment of Potential Impacts and Control Measures
Vessel type
Fuel Use
(te) 1
Emissions (te)
CO2 NOx N2O SO2 CO CH4 VOC
Anchor handling vessel 3,820 12,224 227 0.84 15.28 60 0.69 7.64
Supply vessel 2,970 2 9504 176 0.65 11.9 46.6 0.53 5.94
Standby vessel 162 518 9.6 0.04 0.65 2.5 0.03 0.32
Total 6,950 22,246 412.6 1.53 27.83 109.1 1.25 13.9
1
Total fuel use assuming three Cawdor wells.
2
This is assuming the supply vessel is at worst only serving one rig each trip. This tends to be unlikely
and therefore represents the worst case.
Note; Atmospheric emissions have been calculated using emissions factors from EEMS Atmospheric
Calculations Issue 1.810a (Austin, 2008)
Table 5‐3 Summary of emissions associated with the drilling support vessels.
Proposed Control Measures
The drilling rig will be subject to audits ensuring compliance with UK legislation.
The impact from emissions will be mitigated by optimising support vessel efficiency.
Low sulphur fuels will be used in accordance with prevailing EU and MARPOL requirements.
EMISSIONS TO AIR FROM WELL CLEANUP AND WELL TEST
A screening assessment of the significance of the environmental risk associated with emissions to air
from well clean‐up and well test operations was undertaken. The assessment indicated the risk to be
low due to the low volumes of oil and gas flared and the short duration of activities. However, such
activities may contribute to the greenhouse effect, acid rain and local air pollution.
Well clean‐up is necessary to ensure the well no longer contains any drilling and completion related
debris (mud, brine, cuttings) which could potentially damage the topsides when completion and
production begins. A well test flow period may be required to obtain reservoir properties, flow rate
information and fluid samples dependent on the information obtained during the drilling of the
reservoir section. Emissions of CO2, CH4 and VOCs are higher during clean up and well test operations
than similar emissions from rig and vessel activities associated with drilling and completions.
A maximum of 2,151 tonnes of hydrocarbons (1,450 tonnes of liquids and 701 tonnes of gas) will be
flared over no greater than a 24 hr period as part of the clean up and well test operations associated
with each well. Assuming that a maximum of 3 production wells are drilled at Cawdor this will result
in the flaring of 3,384 te of liquid and 1,805 te of gas.
Atmospheric emissions resulting from the well test and clean up have been calculated using emissions
factors from the EEMS Atmospheric Calculations Issue 1.10 (Austin, 2008) and are presented in Table
5‐4. From Table 5‐4 it is evident that the emissions from the Cawdor wells clean up and well testing
activities will account for a very small portion (e.g. for CO2 = 0.4%) of the total emissions produced as
a result of well testing in UKCS waters.
D/4114/2011 5 ‐ 3