Environmental statement - Flyndre and Cawdor - Maersk Oil

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5‐ 2 Flyndre and Cawdor Environmental Statement Section 5 Assessment of Potential Impacts and Control Measures This section covers the assessment of all impacts apart from those associated with accidental releases of hydrocarbons. Following DECCs latest guidance on oil pollution emergency preparedness issued on 23 rd December 2010 a separate section encompassing hydrocarbon spills, their impacts and Maersk Oil’s response has been provided in Section 6. The hydrocarbon spill scenario covers both an uncontrolled release of hydrocarbons (well blow out) and also the loss of the diesel fuel inventory of the drilling rig. 5.1. DRILLING PHASE Section 5.1 deals with the environmental impacts associated with the drilling phase of the Flyndre and Cawdor development and the proposed mitigation measures against them. 5.1.1. EMISSIONS Gaseous emissions contribute to global atmospheric concentrations of greenhouse gases, regional acid loads and in some circumstances low‐level ozone and photochemical smog formation. The main greenhouse gases are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and halogenated fluorocarbons (the latter are now strictly controlled under the Montreal Protocol). EXHAUST EMISSIONS FROM RIG AND SUPPORT VESSELS Section 2 discusses the predicted duration of the drilling phase and the likely support vessels required for the development. The predicted atmospheric emissions that will result from this are given in Table 5‐2. The emissions have been calculated using emission factors from the EEMS Atmospheric Calculations Issue 1.801a (Austin, 2008) and have been presented as a percentage of total emissions in 2009 from drilling activity in the UKCS. Fuel use (te) Emissions (te) CO2 NOx N2O SO2 CO CH4 VOC Drill Rig 2,220 1 7,104 132 0.49 8.88 35 0.40 4.44 2009 total rig emissions 261,928 4,875 18 245 1,288 35 144 Rig emissions during drilling of Cawdor wells as a % of 2009 total rig emissions 1 Total fuel use assuming three Cawdor wells 2.7 2.7 2.7 3.6 2.7 1.1 3.1 Table 5‐2 Summary of emissions associated with drilling of the three Cawdor wells. The atmospheric emissions from vessels associated with drilling activities are given in Table 5‐3. These emissions have been combined with the atmospheric emissions from installation vessels to allow calculation of cumulative emissions when compared to UK total shipping emissions (Table 5‐5).
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
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Environmental statement - Flyndre and Cawdor - Maersk Oil

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