Zinc is a 10 slot subsea production template and manifold installed in awater depth of 1460 feet in the Exxon Mississippi Canyon Block 354 Field in theGulf of Mexico. Zinc, which is located approximately 50 miles south of GrandIsle, produces through three flowlines to the Exxon Alabaster Platform locatedin Mississippi Block 397 approximately 6 miles to the west of Zinc. AnElectrohydraulic Multiplexed Control System provides for control and monitoringof the Zinc subsea and platform equipment.
This paper describes Exxon's maintenance and remedial action approach forthe Zinc Subsea Control System. A companion overview paper describes theequipment resulting from this approach.
Subsea equipment reliability/availability is a critical factor in keepingsubsea wells on production, and thus in maximizing a subsea project's economicreturn. Equipment availability is dictated by the combination of (a) theequipment's inherent reliability, (b) the levels of redundancy provided, (c)the capability to perform routine equipment inspection, performance evaluation, and maintenance, and (d) the timeliness that repairs can be effected whenrequired. The challenge for the Zinc Project Team in providing for maintenanceand repair capabilities was to achieve a proper balance of these factors, thusbalancing the project's initial investment and operating costs.
Zinc has a planned production life of 20 years. To be assured of achievingthis production life, considerable maintenance capabilities have beenincorporated into the Zinc equipment. The most extreme of these capabilities isretrieval and reinstallation of the Zinc Subsea Production Manifold, whichcontains all manifold piping and valves, the Subsea Control System equipment, and the hydraulic distribution network. This is done independently of theSubsea Template; however, to do so will require that all wells be killed andsuitably plugged and the X-mas Trees removed.
Retrieving and reinstalling the Subsea Manifold for repair will be verycostly and not without risk to the wells and equipment. To minimize the chancesof having to undertake this operation due to control system failure, the ZincElectrohydraulic Multiplex Subsea Control System equipment has incorporatedsubstantial redundancy and maintenance provisions as the clearly preferredmeans of repair.