Germany’s biggest oil reservoir and its most productive oilfield is located deep below Schleswig Holstein’s Wadden Sea, around eight kilometres from the Dithmarschen coast. In view of the sensitivity of the eco-system, a unique drilling and production island was developed and constructed. The latest technology and highly qualified technicians were employed for the construction of the Mittelplate island. This combination ensured an optimum safety package, guaranteeing reliable protection of the environment during oil production on the Mittelplate to this day. The safety and environmental protection measures that were applied have set standards and perform an international exemplary function.
Protection and safety ensured by complete separation
The basic principle of the Mittelplate is on the one hand to protect the island from the forces of nature and on the other hand to separate it from the outside world to protect the environment. For that reason, the 70 x 95-metre drilling and production island was constructed as a leakproof steel and concrete basin on the tidal sandflats. The external sheet piling walls are eleven metres high. Nothing leaves the island unchecked. Even seepage is excluded. Nothing can get in, apart from rain and spray. The design, selected according to thorough hydrographical, water flow-related and meteorological investigations, offers optimum strength and stability. The entire structure is also permanently protected against erosion.
The North Sea is not polluted
The principle of separation extends to everything that could affect the environment.
- Nothing leaves the island unchecked.
- The wastewater from the living and kitchen areas is cleaned in a wastewater treatment plant, then collected in tanks and disposed of on land just like the solid waste.
- The water recovered with the oil is separated and fed back into the reservoir. This is a closed system.
- The solid basin structure, designed to withstand extreme loads, has another advantage. The impermeable surface of the island, sealed by specially developed concrete and the sheet pile walls, could hold far more oil than is stored on the island at any one time. The extensive pipe and cable ducts are also sealed against oil leakage, as are the large rig cellars.
Seamless disposal system for drilling operations
The Mittelplate’s seamless disposal system ensures safe drilling operations, which do not pollute the North Sea. The rig cellar and the boreholes are located inside the sealed concrete basin. During drilling work, the drilling fluid brings sand and cuttings to the surface. It is separated on the Mittelplate and taken ashore in containers for processing.
Monitoring and control systems for all areas of operation
Production work is controlled and monitored around the clock by control systems and technicians. There are multiple safeguards against possible risks. If there are any problems during production, the oil pumps switch off automatically and the subsurface safety valve closes the borehole. More closing valves on the well head provide additional security against rises or falls in pressure.
As all the process tanks are connected to a closed system by means of vapour recovery pipes, emissions can be prevented. The associated oil gas produced with the oil is separated and used to generate power and heat in a sound-insulated gas turbine.