Design and Application of a Dynamic Flexible Pipe Array for Placid's GC 29 FPS

Abstract

Placid Oil Company has installed the first floating production system in the Gulf of Mexico using unprecedented technology. The technology includes a complex rigid-flexible combination riser system. The riser allows production and surface control of each subsea completed well, as well as export of separated oil and gas between a subsea production template and a semi-submersible drilling rig that was modified to allow simultaneous drilling and production operations. Flexible pipe segments, suspended between the semi-submersible's pontoons and the top of the free standing rigid riser, are essential components of the combination riser. The flexible pipes accommodate significant differential motion between the floater and the upper connector of the free standing riser. They are designed to withstand hurricane extreme environmental conditions while enabling the riser to remain connected to the rig. This paper presents the various phases of engineering, manufacturing and installation of the flexible pipe elements. Particular emphasis is placed on engineering methodology used in this frontier development to design a system that accommodates large differential motions in an extremely confined space. INTRODUCTION Placid Oil has installed a subsea production template capable of supporting 24 subsea wells in 1530 feet of water on Green Canyon Block 29. Three satellite trees, one located in adjoining Ewing Bank Block 999 and two in Green Canyon Block 31, are tied back to the template. Two export pipelines, one 16 inch for gas export and one 14 inch for oil, enable production to be sent to shore. Top side process facilities and drilling capability are provided by Penrod 72, a semi-submersible rig converted to drilling, workover and production modes. Flowpaths between the floating production system and the template are provided by a buoyant, self standing rigid/flexible combination riser. The rigid segment of the riser is made buoyant by the use of syntactic foam modules and pressurized air cans (Figure 1). This paper addresses various aspects related to the engineering, manufacturing and installation of the flexible pipe elements of the rigid/flexible combination riser. Flexible pipe is an essential element that renders the concept feasible. PROJECT START UP The contract for engineering and manufacture of the flexible pipe jumpers of the riser system was awarded in February 1986 for a planned installation in February 1987. The contract called for delivery of 27 lines, including a spare 8 inch export line. The 27 lines consisted of:24 production/annulus flowlines: 2.3 inch I.D., 7500 psi working pressure, 11250 psi test pressure, 300 ft long.2 oil export lines: 8 inch I.D., 2160 psi working pressure, 3240 psi test pressure, 300 ft long.1 gas export line: 12 inch I.D., 2160 psi working pressure, 3240 psi test pressure, 300 ft long. The gas export jumper and 12 of the production jumpers were suspended between a porch installed on the port side pontoon of Penrod 72 and the top of the free standing riser.