Troika- Towed Bundle Flowlines

Abstract

Troika is a deepwater (2,700 ft) oil development located in the Gulf of Mexico approximately 150 miles south of New Orleans, Louisiana. The reserves are being recovered through an 8 slot manifold cluster subsea production system1,2 in Green Canyon (GC) 200 tied back to the Bullwinkle platform in 1,350 ft water depth in GC 65. Commingled flow from 5 initial wells will be produced to Bullwinkle through two 14mile long 10-in. diameter pipe-in-pipe insulated flowlines. Well control is maintained with an electro-hydraulic control system through separate electrical and hydraulic/chemical umbilicals. The two 14 mile long flowlines were installed by the bottom tow method in four 7 mile long segments. Each 7 mile segment was fabricated at a beach makeup site, laterallylaunched, bottom towed 400 statute miles, positioned in the field and connected. Connection to the Bullwinkle platform entailed lifting the riser end to the surface and securing it to the jacket leg in a catenary configuration. Insulated steel pipe jumpers were used to join the 7 mile sections at the mid and subsea manifold end points. This paper presents the design, fabrication and installation of the Troika flowlines. Introduction The Troika subsea development is depicted in Fig. 1. Two identical 14 mile long pipe-in-pipe insulated flowlines deliver the well fluids (37° API oil with a Gas-Oil-Ratio of approx. 1800 scf/bbl) from the subsea manifold to the Bullwinkle platform. Each 14-mile flowline is comprised of two 7-mile bundle segments connected together with a midline jumper. The first 7-mile segment consists of the 2,400 ft long steel catenary riser (SCR), flowline bundle and midline sled. The second 7-mile segment consists of a midline sled, flowline bundle and manifold sled. The SCR at Bullwinkle is comprised of a lO-in. production pipe inside an 18-in. casing pipe. The flowline bundle is comprised of a lO-in. production pipe inside a 24-in. casing pipe. By use of a pigging valve and well isolation valves on the subsea manifold, the two flowlines can be isolated for selective well flow or made into a continuous loop for round trip pigging from the Bullwinkle platform. The inset view in Fig. 1 shows the cross section of the pipe-in-pipe configuration along the flowline. The pipe-in-pipe design is utilized to achieve the thermal insulation properties needed to mitigate against paraffin deposition and hydrate formation. The Integrated Project Team (IPT) provided the overall project management and coordinated the design, tow route survey, procurement, fabrication, installation, connection and hydrotest phases of the project. Preliminary engineering for the flowlines began in the 1st quarter of 1996 when both lay and tow methods were evaluated. The towed bundle installation method was selected for the flowline installations in August 1996. The first 7 mile bundle was completed and launched 11 months later in early July 1997. All bundle installation, connection and hydrotest activities were completed successfully by the end of October 1997. First oil was produced November 11, 1997. Like all previous tows in the Gulf of Mexico, the flowline bundles were fabricated along the beach on the Matagorda Peninsula. After fabrication, each 7-mile bundle was cradled into the surf and charged with nitrogen.