POSITION DETERMINATION FOR DYNAMICALLY POSITIONED VESSELS IN DEEP WATER
Many offshore oil fields are in water deep enough that the use of drilling platforms or vessels mounted or moored to the sea bed is not practicable. Therefore, dynamically positioned vessels are used for drilling operations. These vessels are not attached to the sea bed, but use thrusters coupled with a closed loop control system to maintain their position over the well. The control system requires real-time information on the position of the ship relative to the wellhead in order to maintain position. This information is typically provided by an acoustic system. However, there are several occurrences which can cause loss of the acoustic signal. Consequently, a backup position measuring system is necessary to provide satisfactory performance. The approaches commonly used today to provide this backup information are not satisfactory for water depths greater than approximately 1500 feet. This paper discusses a new approach to provide backup position measurements which uses angle measurements at the top and bottom of the marine riser. Computer analyses have shown that the new approach yields position errors of one percent or less of water depth for depths of up to 6000 feet. These analyses have indicated that the concept is feasible for greater depths. Section (2) presents a brief discussion of dynamic ship positioning. Requirements for a position measurement system are presented in Section 3. A discussion of the two approaches most commonly used to obtain backup position data is contained in Section 4. The remainder of the paper is devoted to discussion of the new approach.
Society of Naval Architects and Marine Engineers601 Pavonia Avenue
Jersey City, NJ USA 07306-2907
- Cooper, D L
- Publication Date: 0
- Pagination: 11 p.
- TRT Terms: Analysis; Bow thrusters; Data processing; Drilling; Drilling ships; Dynamic positioning; Underwater construction
- Uncontrolled Terms: Computer aided analysis
- Old TRIS Terms: Deep water drilling; Positioning control systems
- Subject Areas: Marine Transportation; Operations and Traffic Management;
- Accession Number: 00174003
- Record Type: Publication
- Source Agency: Society of Naval Architects and Marine Engineers
- Files: TRIS
- Created Date: May 3 1978 12:00AM