Environmental Statement - Maersk Oil

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2.5.4. METERING 2 ‐ 18 Figure 2‐11 Cooling spool assembly. Balloch Field Development Environmental Statement Section 2 Proposed Development Metering of Balloch production will be via dedicated tree‐mounted multiphase flow meters. The lift gas flow meter for Balloch will be installed on the drop down spools on the tree. Controls for these meters will be connected to the tree’s subsea control module. 2.5.5. SUBSEA CONTROL, INSTRUMENTATION AND CHEMICALS The Balloch wells will require the following services: High pressure (HP) hydraulics (345 barg); Low pressure (LP) hydraulics (207 barg); Power and signal facilities; Chemical injection (methanol and scale inhibitor). The Balloch control will be delivered by a subsea umbilical. It is anticipated that chemicals currently deployed for Donan and Lochranza production fluids will also be suitable for Balloch production fluids. To mitigate against fluid compatibility uncertainty, the Balloch wells will be completed with downhole chemical injection. 2.5.6. GAS AND CONDENSATE RE‐CIRCULATION SYSTEM Balloch gas is very rich (i.e. contains components such as butane and propane) and is anticipated to increase the loading on the current topside processing. Current practice relies on the condensate being cycled until it reaches equilibrium within the gas and oil export streams. Modelling of the process to demonstrate the extent to which this constraint will influence base production and exactly how much condensate will be generated has identified this as a potential variable. Flowing of the initial appraisal/production well will provide a more detailed understanding of this phenomenon as it is very much dependent on the exact composition of Balloch fluids and how they interact with Donan and Lochranza fluids. Models currently predict that the Balloch low to mid case profiles can be accommodated within existing processing capacities. There is some technical risk as to whether the high case can be accommodated, but the recently drilled L3Z well has gone some way to mitigating that risk by producing a spot rate of 32,000 bbl/d and an initial average of over 21,000bbl/d. Lochranza fluids are richer than those from Donan, which goes towards supporting the basis that the current GPIII condensate re‐circulation can be optimised and GPIII can handle richer gas throughputs to accommodate the Balloch fluids.
Balloch Field Development Environmental Statement Section 2 Proposed Development GPIII operations and production chemists will continually monitor this constraint and manage GPIII base production. Should this constraint become unacceptable, as part of the ongoing GPIII production management there are condensate handling mitigations that have been identified. De‐ bottlenecking options would be further pursued in the event they are required. 2.5.7. ISOLATIONS AND HOOK‐UP Double block and bleed production isolations currently exist on the DC2 manifold. The Balloch wells can be hooked‐up to the DC2 manifold without the need for production shutdown or extensive flushing of production or lift gas flowlines. Flushing and isolation risk assessments will be prepared and detailed methodologies completed prior to operations. 2.5.8. PIPELINE TESTING AND COMMISSIONING After pipe lay, the pipelines will be hydro tested prior to production to ensure they maintain pressure and do not leak. As part of this process, the pipelines will be flooded with potable water dosed with biocide, oxygen scavenger, dye and corrosion inhibitor. Following the leak test, the pipeline systems shall be de‐watered using dyed Monoethylene Glycol (MEG) and treated seawater. The potable water, along with chemical additives, may be discharged to the sea surface or processed through existing facilities and re‐injected with the produced water stream. The chemicals to be used for pipeline testing have yet to be finalised; however, the dose and quantities will be in accordance with the manufacturers’ specifications. For the purposes of this ES, it is assumed that all displaced water will be discharged overboard. Details of the disposal of pipeline testing chemicals will be provided in the subsequent PON15C. 2.5.9. SUBSEA INFRASTRUCTURE PROTECTION Concrete mattresses and grout bags will be required to provide protection to the subsea infrastructure associated with the proposed Balloch development. It is estimated that a maximum of 30 concrete mattresses and 15 grout bags will be required for the complete development, i.e. assuming three production wells. The mattresses will measure 6 x 3 x 0.15 m (L x W x H) and have a mass of 2.4 te each while the grout bags will measure 1 x 0.5 x 0.5 m (L x W x H) and have a mass of 1 te each. 2.5.10. SUBSEA INSTALLATION SUPPORT VESSELS Vessel type, duration and fuel usage for the installation of the subsea infrastructure are given in Table 2‐13. Table 2‐13 Vessel use and fuel demand associated with the installation of the subsea infrastructure. Vessel type 1 Phase I; appraisal/production wells Duration (days) Working fuel consumption (te/d) 1 Total fuel use (te/d) Diving Support Vessel (transit) 8 22 176 Diving Support Vessel (working) 30 18 540 Phase II; second and third production wells Diving Support Vessel (transit) 2 16 22 352 Diving Support Vessel (working) 60 18 1,080 1 Source: The Institute of Petroleum (2000) 2 It is assumed that the second and third wells will be drilled at different times, requiring the vessels to go offsite between the drilling of each well. Similarly it is expected that the DSV will go offsite between the drilling campaigns. 2‐19
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B ‐ 2 Halocarbon release during e
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Major accidental events Other envir
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Environmental Statement - Maersk Oil

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