Design Of Insulated Flowlines For Mobile Bay

ABSTRACT Insulated CRA flowlines are used in Mobile Bay for connecting well templates to host processing platforms. This paper describes the design of the flowline insulation system. Design issues for structural integrity are presented. Inlet temperatures of up to 200°F and operating pressures of up to 11,000 psi are accounted for. The flowline system consists of a 4-inch CRA pipe in an 8-inch carbon steel jacket. INTRODUCTION Gas reserves in three offshore fields in the Mobile Bay area are being developed; the Bon Secour Bay Field (inside Mobile Bay), the Northwest Gulf Field (south of Dauphin Island), and the North Central Gulf Field (south of Fort Morgan Peninsula). Water depths in the area range from 10 to 50 feet. Insulated subsea flowlines were designed to connect three 8-pile production platforms to seven remote well templates, while a gathering system connects the production platforms to an onshore processing plant in south Mobile County. The primary fluid service is hot, high pressure, sour gas. The flowline system consists of two fluid conduits, produced gas and dilution water, and an 8 Kv rated electric power cable. Deoxygenated dilution water is pumped from shore to the production platforms and then to the well templates for use in flushing out the wells to dissolve salts. Power is supplied from the production platforms to the well templates. The produced gas flowline design pressure is based on shut-in tubing pressures of 8700 psi for Bon Secour Bay and North Central Gulf Fields and 11,000 psi for Northwest Gulf Field. The design flowline temperature is based on a maximum cooler inlet temperature of 2000 F. The flowline is Insulated to prevent hydrate formation under reduced f10wrates during winter months. The flowline field arrangement (In Figure 1) includes the following:Bon Secour Bay (BSB) Field Production platform In Alabama State Block 62 connected to a remote well template In Alabama State Block 63 with two (2) gas flowlines, two (2) dilution lines, and one (1) power cable.North Central Gulf (NCG) Field Production platform In Alabama State Block 115 connected to a remote well template In Alabama State Block 114 with one (1) gas flowline, one (1) dilution line, and one (1) power cable.Production platform in Alabama State Block 115 connected to a remote well template in Alabama State Block 827 with one (1) gas flowline, one (1) dilution line, and one (1) power cable.Northwest Gulf (NWG) Field Production platform In Alabama State Block 112 connected to a remote well template In Alabama State Block 112 with one (1) gas flowline, one (1) dilution line, and one (1) power cable.Production platform In Alabama State Block 112 connected to a remote well template In Alabama State Block 868 with one (1) gas flowline, one (1) dilution line, and one (1) power cable.