Sea, North

Taking into consideration that some of the structures in the North Sea are of unprecedented dimensions and that most of the problems encountered are of a type which has never been tackled before, it is easily understood that the work with these structures has been an exciting challenge. 

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For more than a century petroleum geologists have been looking for oil. During this period major discoveries have been made in many parts of the world. However, it is becoming increasingly likely that most of the giant fields have already been discovered and that future finds are likely to be smaller, more complex, fields. This is particularly true for mature areas like the North Sea. 

Introduction and commercial application Safety and the environment have become important elements of all parts of the field life cycle, and involve all of the technical and support functions in an oil company. The Piper Alpha disaster in the North Sea in 1988 has resulted in a major change in the approach to management of safety of world-wide oil and gas exploration and production activities. Companies recognise that good safety and environmental management make economic sense and are essential to guaranteeing long term presence in the industry. 

The UK government enquiry into the Piper Alpha disaster in the North Sea in 1988 has had a significant impact on working practices and equipment and has helped to improve offshore safety around the world. One result has been the development of a Safety Management System (SMS) which is a method of integrating work practices, and is a form of quality management system. Major oil companies have each developed their own specific SMS, to suit local environments and modes of operation, but the SMS typically addresses the following areas (recommended by the Cullen Enquiry into the Piper Alpha disaster) ... 

Environmental vulnerability varies considerably from area to area. For example the North Sea, which is displaced into the Atlantic over a two year period,-is a much more robust area than the Caspian Sea which is enclosed. Regional standards should reflect those differences. 

With a few exceptions reservoir rocks are sediments. The two main categories are siliciclastic rocks, usually referred to as elastics or sandstones , and carbonate rocks. Most reservoirs in the Gulf of Mexico and the North Sea are contained in a clastic depositional environment many of the giant fields of the Middle East are contained in carbonate rocks. Before looking at the significance of depositional environments for the production process let us investigate some of the main characteristics of both categories. 

If compaction occurs as a result of production careful monitoring is required. The Ekofisk Field in the Norwegian North Sea made headlines when, as a result of hydrocarbon production, the pores of the fine-grained carbonate reservoir collapsed and the platforms on the seabed started to sink. The situation was later remedied by inserting steel sections into the platform legs. Compaction effects are also an issue in the Groningen gas field in Holland where subsidence in the order of one meter is expected at the surface. 

Steel piled jackets are the most common type of platform and are employed in a wide range of sea conditions, from the comparative calm of the South China Sea to the hostile Northern North Sea. Steel jackets are used in water depths of up to 150 metres and may support production facilities a further 50 metres above mean sea level. In deep water all the process and support facilities are normally supported on a single jacket, but in shallow seas it may be cheaper and safer to support drilling, production... 

The legs of the platform can be used as settling tanks or temporary storage facilities for crude oil where oil is exported via tankers, or to allow production to continue in the event of a pipeline shut down. The Brent D platform in the North Sea weighs more than 200,000 tonnes and can store over a million barrels of oil. Topside modules are either installed offshore by lift barges, or can be positioned before the platform is floated out. 

Ship-shaped FPSOs must be designed to weather vane i.e. must have the ability to rotate in the direction of wind or current. This requires complex mooring systems and the connections with the well heads must be able to accommodate the movement. The mooring systems can be via a single buoy or, in newer vessels designed for the harsh environments of the North Sea, via an internal or external turret. Figure 10.33 shows a schematic of the Shell-BP Foinaven FPSO. 

For a typical operation in the North Sea, the transport of personnel to and from the facilities is by helicopter. The transport of materials is normally by supply boat. 

Introduction and commercial application Investment opportunities in the exploration and production (E P) sector of oil and gas business are abundant. Despite areas such as the North Sea, Gulf of Mexico and the North Slope in Alaska being mature areas, there are still many new fields under development in those regions, and new areas of business interest are opening up in South America, Africa and South East Asia. Some fields which have a production history of decades are being redeveloped, such as the Pedernales Field in Venezuela. 

A new approach of partnership between client and inspection service organisations has been established primarily for the North Sea but increasingly finding application elsewhere Benefits accrue to all parties and the technical and commercial lessons learnt in the process have relevance to a wide range of other industries. 

T. Sevel, E. March and N.H. Pedersen, North Sea Flaw Measurements Workshop, 1995, Lillehammer, Norway... 

T. Sevel, NH. Pedersen, C.E. Weinell, B. Lind-Nielsen, North Sea Flow Measurements Workshop, 1996, Peebles, Scotland... 

Ammonium chloride [12125-02-9], ammonium sulfate [7783-20-2], and diammonium phosphate [7708-28-0] have also been used for shale stabilization (102,103). Ammonium ions have essentially the same effect on shales as potassium ions but use of ammonium salts is often objectionable because of the alkaline nature of the mud. In the North Sea and northern Europe, where magnesium-bearing salt formations ate encountered, magnesium chloride [7786-30-3] is used, but in the United States it is used only on a small scale. 

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