The Removal of the Maureen Steel Gravity Platform

Abstract The Maureen drilling, production and oil storage platform is located in 95.6m of water in block 16/29 of the U.K. Continental Shelf, and consists of a large integrated deck structure having production, drilling, and quarters facilities which in turn is supported off a steel gravity platform structure having an integral 650,000 barrels of oil storage. The Maureen platform and the field development at the Maureen location is entirely unique from anything developed elsewhere in the North Sea and the rest of the world. The platform was installed in 1983, and is at the end of its useful production life whilst at the Maureen location. It is planned to remove the platform from the seabed and to tow the complete structure to a safe inshore deep water anchorage, in order to either execute any modifications necessary for platform re-use, or to complete the onshore disposal of the entire platform. This paper addresses the main technical problems and procedures associated with the extraction of the 110,000 tonnes platform from the seabed, the subsequent deballasting to a towing draft, and the tow to a deep water inshore location. Introduction The Maureen oil field is located in block 16/29 of the UKCS, and was initially developed with the installation of the Maureen gravity platform and integrated deck structure, having oil export through a seabed pipeline to a concrete articulated loading column, and thence to an export tanker. Subsequent developments tied in the Moira field with a subsea wellhead structure connected via pipelines and umbilical to the main platform. Figure 1 provides a schematic layout of the Maureen facilities at the location. The concept of using a steel gravity platform with integral oil storage for early production in the North Sea has been described previously (1). The field was initially developed with pre-drilled wells running through a seabed template structure, which in turn was initially connected to two 84 inches diameter docking piles located at the seabed. The docking piles were used during the platform installation in order to accurately control the final position of the Maureen platform over the pre-drilled wells located within the template structure. The Maureen field is now coming towards the end of its production life, and this will entail the decommissioning and removal of the facilities at the Maureen location. By far the most technically interesting aspects of decommissioning and removal of the Maureen facilities is the removal of the Maureen platform, and this paper mainly concentrates on this aspect. The platform removal and re-float operations require several systems to be operational, and these are listed below :–ballasting/deballasting system–compressed nitrogen system–compressed air system–control system–underbase water/mud injection system–electrical power generation–marine fleet For purposes of providing an outline of the procedures for the removal of the Maureen steel gravity platform from the location, an outline of the operations have been divided into seven main phases, which are described in more detail in subsequent sections :-–platform preparation–pre re-float tests–pre charging storage tanks with compressed nitrogen, and deballasting/dewatering of secondary spaces–underbase soil pressurisation and soil breakout–float-up