Installation of ROV-Friendly Cathodic Protection Systems on Two Deepwater Subsea Developments

by D.K Flanery, J Britton, K Thompson and P Sandy (2009)

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Two deepwater subsea production fields, Arnold and Oyster, started producing in 1998 in the Ewing Bank Area of the Gulf of Mexico. The fields contain a total of four subsea wells with wet trees and flow lines back to a fixed platform. Water depths range between 770 feet (235m) and 1,758 feet (536m). During routine surveillance it was noted that some anodes on the well trees and flow lines had excessive depletion. Since the field was undergoing expansion it was decided to supplement the cathodic protection (CP) systems on all the assets to provide an additional 20 years life. This paper describes the CP design and ROV-friendly methodologies used to install 19 anode arrays with 21 clamped tiebacks onto four flow lines and eight subsea components in 73 hours. Details on initial system performance verification will also be presented.

Figure 1: Arnold Field Layout with Anode Pods, Tie-Back Cables and Clamps

Figure 2: Oyster Field Layout with Anode Pods, Tie-Back Cables and Clamps

Figure 3: Anode Pods, Tie-Back Cables and Clamps Preassembled Dockside

Figure 4: Custom clamp engaging the member of Oyster Umbilical Termination Assembly

Figure 5: Anode Pod set on seabed

Figure 6: ROV disconnecting crane rigging from Anode Pod

Figure 7: Clamp connected to flowline; Contact Probe testing for electrical continuity

Figure 8: Clamp engaging the member of a Well Tree

Figure 9: Arnold SDU – Intended clamp location (striped arrow); Actual clamp location (solid arrow)

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