Grondin North East Experimental Station - Diverless Experiments

ABSTRACT Various diverless experiments have been performed during 1979/1980 on the GRONDIN North East subsea production station installed by ELF AQUITAINE in Africa, offshore GABON. Operating and maintenance requirements for a deep water subsea production system are discussed. Main results of the performed experiments are given. Two kinds of diverless techniques studied and then experimented are described:A rail mounted remote manipulator was specified, designed, built and then installed on the GRONDIN subsea station and remotely operated from a surface support. Various functions have been performed: electric and hydraulic connection, jumper pipe assembly, opening and closing of valves.A manipulating arm has been fitted on a manned submarine. This arm can be equipped with specific tools remotely operated from inside the vehicle. Guide lines connections, opening and closing of valves, control of the above mentioned rail mounted manipulator have been made on the GRONDIN subsea station. These experiments were conducted with success and a first conclusion about such systems can be drawn indicating the trends and the aim of a possible improvement. INTRODUCTION The GRONDIN N.E. subsea experimental station was installed during 1976/1977 in 200 feet of water, 1500 meters North-east of the fixed platform complex on the GRONDIN field of ELF GABON, offshore the Republic of GABON, west Africa. The station has dual objectives: Produce oil from the North-east extension of the GRONDIN field. Permit experimentation to prepare ELF AQUITAINE for producing oil in deep waters and in difficult locations. The subsea station includes three subsea wellhead assemblies mounted on a template which is equipped with the required manifolds, flow-lines, and control cables to tie the station to the production facilities on the GRONDIN platform. Wellhead functions are remotely controlled from the platform. Installation, connections and maintenance operations are conducted from a floating service vessel (Barge "Anguille"). Although the subsea station is installed in 200 feet of water depth, a 2000 feet depth limit has been selected for the design and experimental performance of the various equipment and procedures tested. Divers assistance to install, operate and maintain such a deep water subsea production system (2000 feet) cannot be envisaged. So, ELF AQUITAINE has initiated a research program to develop some tools to be experimental on the GRONDIN subsea station, using diverless techniques. The choice of equipment and procedures for economic development of subsea production systems is influenced not only by water depth but by other factors as well including wind and sea conditions, air and water temperature, shipping, ice flows and earthquakes, to mention a few. Because some equipment may be unique and applicable to a specific set of conditions while other equipment may be wide ranging in application, the GRONDIN N.E. Station and the associated experimental program have been designed to test full-size versions of a variety of equipment and systems. Among this various experimental equipment tested on the GRONDIN subsea station two prototypes have been built and experimented during 1979/1980, to perform diverless operations: