Three flowlines are used to transport the gas produced from the Exxon Zincsubsea production template (in MC355) to the Alabaster platform (in MC397). Each flowline installation was initiated from Alabaster with a J-tube pull andlaid down into target areas at Zinc. Diverless subsea connections at Zinc werecompleted using the second end lateral deflection method and a diverlessROV-operated collection system.
The Zinc subsea production system is a gas development in 1460 feet ofwater, located in the Mississippi Canyon area of the Gulf of Mexico. Fullwellstream production will be delivered to the Alabaster platform located 6miles to the West in 468 feet of water through a dual 8-inch and single 4-inchflowline system.
The 4-inch flowline is designed for a maximum working pressure of 5000 psito transport gas from the high pressure wells. The 8-inch flowlines aredesigned for a maximum working pressure of 3705 psi to transport gas from thelow pressure wells. Table 1 summarizes the characteristics of the threeflowlines. The maximum working pressures were selected to withstand wellshut-in pressure.
The flowlines and associated piping are designed to allow pigging operationsfrom the Alabaster platform through a removable Pigging Valve Assembly (PVA) onthe manifold piping of the subsea template. The PVA is controlled fromAlabaster through the control system at Zinc and can be configured for variouspigging operations. The dual 8-inch lines allow round trip pigging operationsto be carried out from Alabaster. A parking block in the PVA also allows an8-inch pig to be parked and returned through the same 8-inch line. Pigging ofthe 4-inch line can be performed by pumping the pigs from Alabaster and dumpingthem into the 8-inch loop at Zinc or by using a parking block on the PVA whichallows the pig to be returned to Alabaster in the 4-inch line.
