Upending Control System for the Ninian Field Southern Platform

ABSTRACT This paper describes the latest "state-of-the-art" equipment developed for controlled flooding and upending of very large offshore oil drilling platforms with built-in flotation. Because of the large-size and cost of these platforms which must be set accurately in place under less than ideal sea conditions, much effort is required to design, detail, construct and operate reliable and versatile flooding systems. The philosophy of design to arrive at systems which will operation under most foreseeable situations is discussed. Redundancy of components and alternatives to cover possible field breakdown are covered. A brief look into details of air hydraulic valve operation are included with discussions of manual, electric and remote radio coupled systems for operation of mechanical components. Methods of protecting equipment and personnel in a submerged environment are described. The flooding system developed for this project was highly successful in remotely upending the Ninian Southern Platform. Predecessor systems were also used with excellent results on the Maui, Brent and Thistle Platforms. The lessons learned and design details are applicable to a variety of future structures in the ocean which must be installed by controlled flooding. Problems in previous systems and how they were overcome are discussed Weaknesses in present methods and suggestions for future improvement are covered. INTRODUCTION With the advent of the very large platforms developed for offshore oil use today it is no longer a matter of simply opening a few valves and lifting the top of the platform with a derrick barge to upend it. The sheer weight of these structures (20,600 tonnes in the case of the Ninian Southern Platform Fig. 1) is well beyond the capacity of even the largest offshore crane ships. Even with a fleet of large lift cranes, the coordination and perfect sea conditions required would make a lift-flood method impractical and abnormally expensive. Also, because of the large dimensions of these structures and the number of tanks to be flooded, manual opening of valves from reach rods at the tower top would be extremely difficult requiring a fair size crew to coordinate. Therefore a system for flooding and upending (See Fig. 2) these types of structures is needed that would be under some sort of centralized control. The control would require rapid response time on opening and closing flood valves. With a tower design such as the Ninian Southern Platform which floats on large buoyant legs, it was possible to add a central control system located on the tower in such a manner that it would not be submerged during the upending. (See Figure 3). DESIRED CHARACTERISTICS AND REQUIREMENTS OF THE UPENDING CONTROL SYSTEM The idea of central control was a good starting point. But, to take the concept one step further, it was desireable that the final control point for upending be located at a safe distance away from the tower. A location on the control ship or crane barge was preferred.