Controlling Export Pipeline Pressure To Optimize Gas Throughput From The Mirage Floating Production Unit

Abstract

Abstract Deep-water production in the Gulf of Mexico and other basins normally relies on tying into existing shallow water transmission lines. Efficient production of the reserves from deep-water fields many times requires the incoming lines be operated at a pressure above that for which the downstream segment was designed or that the applicable codes will allow. ATP Oil & Gas Corporation's (" ATP??) Gulf of Mexico Mirage Field in 4000' of water was no exception to this problem. The results of field-production modeling to optimize reserve recovery clearly demonstrated the field's gas export line required operation at a pressure significantly above that of its shallow water transmission line destination. At an early stage in the project, ATP sought the guidance of both the transmission line operator and the Minerals Management Service. Numerous flowing and shut-in conditions were modeled to insure the resultant protection systems were capable of responding to the full range of expected daily operations. It is expected that the methods and systems thus developed will serve as a template for future deep-water export pipeline system planning and operation. Introduction The Mirage Field is the anchor of the first phase of the development of the Telemark Hub (" Hub??) in the Gulf of Mexico. Mirage (MC 941), Morgus (MC 942) and Telemark (AT 63) together constitute ATP's leases in the area. All of these had been discovered and evaluated by other operators and, for various reasons, been judged below their thresholds for development. ATP acquired all three via farmout or purchase. Along with the gas-export pipeline overpressure protection system, the development solution for the Telemark Hub includes the use of several novel approaches for the Gulf of Mexico. The export pipeline's origin is a first-of-its kind floating production system (" FPS??) that is described in another paper at this conference. The top-tension riser system, mooring installation method, well drilling/completion modes and well-control hardware are also either innovative or on the forefront of deep-water field development applications. The oil export system is a 10?? O.D. line that runs almost due northwest from the platform before turning north and tying into the Mars oil export system in MC Block 718. Its total length is approximately 22 miles. The 10?? gas export system (and topic of this paper) runs parallel to the oil export system but continues northwest until it ties in to the Discovery (" Discovery??) gas export system roughly 63 miles away in GI 115. Both lines originate from the FPS as steel catenary risers. Figure one is a high-level sketch of the general arrangement of the platform and its export system.