TDW Completes Subsea Services on GOM's Independence Trail Pipeline

Subsea Flex-Joint Isolation Ops
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Subsea Ops on Independence Pipeline
(Click to Enlarge)

TDW Offshore Services has successfully completed a key subsea flex-joint isolation operation on the Independence Trail natural gas pipeline for Enterprise Products Partners L.P. in the Gulf of Mexico. The isolation operation allowed critical repairs to be made on the FlexJoint™ assembly of the 20-inch export riser on the Enterprise Independence Hub platform in Mississippi Canyon Block 920 that had begun to leak in April 2008.

Gas Pressure Maintained While Repairs Made

Safe and timely repairs were essential on the leaking subsea flex-joint due to the important role of this natural gas export riser. The Enterprise Independence Hub platform has the capability of handling more than 10% of the natural gas transported from the Gulf of Mexico. Located approximately 85 feet (26 m) below sea level, the FlexJoint allows the riser to withstand the movements of the platform. In order to facilitate the riser repair, Enterprise engaged TDW to isolate this FlexJoint assembly, with its piggable, tetherless, SmartPlug isolation tool.

The platform riser had previously been assessed by TDW for possible isolation with its remote-controlled SmartPlug high pressure pipeline isolation tool. This assessment allowed TDW to quickly mobilize a double block module 20-inch SmartPlug tool to the platform where it was temporarily installed in early May. The tool was launched and pigged (pumped by water) into the riser just below the FlexJoint. This allowed Enterprise to maintain pipeline pressure downstream of the FlexJoint. With ambient pressure above the FlexJoint, divers then replaced the o-ring gasket subsea and then after resealing, the entire riser was successfully pressure tested. Consequently, Enterprise was able to resume the gas flow from its production fields through the riser. The entire isolation operation was completed in just 10 days.

"This was a challenging situation for Enterprise, especially in view of the 134-mile length of the pipeline and the fact that the Steel Catenary Riser (SCR) is operating in a depth of 8,000 feet of water," said Mark Roberts, General Manager Americas for TDW Offshore Services. "The FlexJoint repair was achieved without degassing and flooding the riser, and recommissioning it post repair, which would have been far more costly in terms of production downtime and marine spread cost," he added.

Emergency Preparedness

Assessment of the Independence system for isolation emergencies -- undertaken earlier by TDW -- permitted record breaking response from TDW for isolation of this important 20 inch riser. According to TDW, the Enterprise operation is one of the fastest mobilizations the company has ever carried out, due in part to the advanced preparations of the SmartPlug operation for Enterprise.


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