A High Load Moderate Speed Deployment System for a Deep Ocean Bottom Working Vessel

Abstract

ABSTRACT A working vessel for deploying and retrieving heavy loads in deep oceans is now operational. This is accomplished by lengthening or shortening a load-connected pipe string and by two pair of yoked, hydraulically powered cylinders that alternately support and transport the pipe string and load. This paper describes the deployment and retrieval system. The system, known as the Heavy Lift System, contains four 19-foot stroke hydraulic cylinders and their power units and 8500-ton capacity connecting yokes for each pair of cylinders. Ancillary hydraulic equipment includes a pipe string engaging latch on each yoke, a 450,000 ft-lb pipe string torquing/ detorquing device on one yoke, a stationary support for "parking" and rotating the load and the hydraulic power units for these elements. In addition, the system includes an instrumentation and control suit to automatically or manually operate the complete deployment and retrieval functions. The system has a stall load capacity of 8500 tons. It has been fully tested and successfully used to deploy and retrieve up to 7500 tons at 6 feet/minute in 17,000 foot depths. INTRODUCTION The GLOMAR EXPLORER is the surface support vessel for an operational system designed to work the ocean bottom. It transports the bottom equipment and provides the work platform from which the bottom equipment is operated, deployed and retrieved. Design parameters for deploying/retrieving were much greater than anything previously done from a vessel, and unique equipment had to be devised, tested, installed and operated. The resulting subsystem is called the Heavy Lift. The mechanical link between the Heavy Lift and the bottom equipment is a rigid pipe string. Deploying/retrieving is similar to current offshore riser and drill string operations, i.e., add/remove a pipe stand then lower/raise the pipe string to the next tool joint. Initial pipe string design payload and depth was up to 4,000 tons and 17,000 feet. To minimize pipe string stress and thereby its weight, the work platform for the Heavy Lift was gimballed and heave compensated1. Platform space was limited and any equipment on the platform added to the gimbal-heave compensator loads. Compact and light Heavy Lift components were needed. The design weather window for deploying/retrieving was' small and the necessary lowering/ raising rates could only be achieved by automation which, in turn, requires remotely controllable components. Finally, pipe stands weighed up to 40,000 lbs each, tool joint torque was up to 450,000 ft-lbs and, in spite of the gimbal-heave compensator refinement, the design payload for the Heavy Lift became 8,500 tons at 17,000 ft depths. High rates and high loads necessitated high powered Heavy Lift components. Compact, low weight, remotely controllable and high power components were achieved by designing hydraulically powered mechanical equipment. These were integrated with an electronic control system to meet the Heavy Lift subsystem functional requirements during automated operations.