Environmental statement - Flyndre and Cawdor - Maersk Oil

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Flyndre and Cawdor Environmental Statement Section 2 Proposed Development Structure Dimensions (m x m) Total footprint (m 2 ) Flyndre manifold 5.5 x 5.2 28.6 Cawdor manifold 12.4 x 10.8 133.92 SSIV 5 x 5 25 Table 2‐8 Subsea footprint of manifolds and SSIV associated with the development. The manifolds will be piled to resist accidental loadings arising from interaction with fishing equipment. Four piles will be used to hold each manifold in place, the piles have the following dimensions and penetration depths: penetration length = 15 m outside diameter = 600 mm The seabed conditions are expected to be similar to those found at the Affleck development. Maersk Oil has collected information on the pile driving information required to install piles at the Affleck development. In this case a submersible hammer (IHC Hydrohammer S‐90) and piles that had a diameter of 610 mm were installed to a depth of 16.5 m, details of this are presented in Table 2‐9. At the time of writing this ES it was expected that the drivability results presented here would represent the most onerous driving scenario at the Flyndre and Cawdor fields as the scenario presented is for a greater piling penetration length and a marginally wider outside pile diameter. Hammer Total Blows IHC Hydrohammer S‐90 963 Driving Time (min) 32 24 19 16 13 12 10 9 8 8 Blow Rate (b/min) 30 40 50 60 70 80 90 100 110 120 Table 2‐9 Drivability results summary. The SSIV will be a gravity based structure and will not require piling. 2.6.3. PIPELINE DESIGN Hydrocarbons from the Flyndre and Cawdor fields will be tied back to the Clyde production facilities via a common Subsea 8”/12” pipe‐in‐pipe export pipeline. The Flyndre to Cawdor line is 4.2 km while the Cawdor to Clyde is 20.46 km. A pipe in pipe system was selected for the project as it provides the most robust system with regard to operability and integrity. The carrier pipe material will be carbon steel and a dry insulation will be used within the annulus. 2.6.4. PIGGING REQUIREMENT Routine operational pigging is not envisaged, however to address unforeseen events, the pipeline will be designed to be pigged and the subsea facilities will be configured with a temporary pigging connection at the Flyndre end of the pipeline. The Clyde platform will provide space to enable temporary pig launching/receiving equipment to be installed. 2‐ 12 D/4114/2011
Flyndre and Cawdor Environmental Statement Section 2 Proposed Development 2.6.5. METERING Subsea Multiphase Meters (MPM) will be installed subsea at both the Flyndre and Cawdor manifolds and additional meters will be fitted to the Cawdor trees. 2.6.6. SUBSEA UMBILICALS A static subsea umbilical will be installed between the Clyde platform and the Cawdor manifold (20.46 km) and a second umbilical of similar construction will be installed between the Cawdor manifold and the Flyndre manifold (4.2 km). A breakout point will be located at the SSIV structure to provide controls for the SSIV. The umbilical will supply all required chemicals, hydraulic fluids and electrical power. 2.6.7. SUBSEA INFRASTRUCTURE PROTECTION PIPELINE AND UMBILICAL TRENCHING A pipelay vessel that is equipped with Dynamic Positioning will be used. The pipeline will be laid and trenched and backfilled using a towed plough arrangement (Figure 2‐7). The plough will be used to firstly cut a trench containing the pipeline to a target depth of 1.8 m and then backfilled using a backfill plough. The trench is not envisaged to provide any obstruction to fishing gear that may encounter it. Figure 2‐7 Pipeline trenching plough (CTC Marine, 2011). There are two options for the installation of the subsea umbilical: Trench and mechanical backfill; The main umbilical is laid in a dedicated trench using a towed plough and the trench is either mechanically backfilled or left to backfill naturally. The backfilling operation can be carried out with the same plough as is used for trenching except that the blades are configured differently. Simultaneous lay and trench; A device similar to a pipeline plough (Figure 2‐8) is used to lay and trench the umbilical simultaneously. D/4114/2011 2‐13
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Environmental statement - Flyndre and Cawdor - Maersk Oil

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