Product platforms

The oil and gas industry produces much waste material, such as scrap metal, human waste, unspent chemicals, oily sludges and radiation. All of the incoming streams to a facility such as a production platform end up somewhere, and only few of the outgoing streams are useful product. It is one of the responsibilities of the engineer to try to limit the amount of incoming material which will finally become waste material. 

In this section we describe hydrocarbon processing in preparation for evacuation, either from a production platform or land based facilities. In simple terms this means splitting the hydrocarbon well stream into liquid and vapour phases and treating each phase so... 

The function of offshore production facilities are very much the same as those described for land operations. An offshore production platform is rather like a gathering station hydrocarbons have to be collected, processed and evacuated for further treatment or storage. However, the design and layout of the offshore facilities are very different from those on land for the following reasons ... 

This section describes the main types of offshore production platform and satellite development facilities, as well as associated evacuation systems. 

Subsea production systems are an alternative development option for an offshore field. They are often a very cost effective means of exploiting small fields which are situated close to existing infrastructure, such as production platforms and pipelines. They may also be used in combination with floating production systems. 

The most basic subsea satellite is a single Subsea Wellhead with Subsea Tree, connected to a production facility by a series of pipelines and umbilicals. A control module, usually situated on the subsea tree, allows the production platform to remotely operate the subsea facility (i.e. valves, chokes). 

In recent years much more attention has been given to pipeline isolation, after instances in which the contents of export pipelines fed platform fires, adding significantly to damage and loss of life. Many export and in field pipelines are now fitted with emergency shutdown valves (ESDV) close to the production platform, to isolate the pipeline in the event of an emergency. 

Product quality is not limited to oil and gas quality certain effluent streams will also have to meet a legal specification. For example, in disposal of oil in water, the legislation in many offshore areas demands less than 40 ppm (parts per million) of oil in water for disposal into the sea. In the UK, oil production platforms are allowed to flare gas up to a legal limit. 

Metering oi the production for fiscal (taxation), tariffing and re-allocation purposes may take place as the product leaves the production platform, or as it arrives at the delivery point such as the crude oil terminal. If the export pipeline Is used by other fields (including third party users) it would be common to meter the production as it leaves the platform. 

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To recover oil from the continental shelf of arctic Canada and Alaska, drilling and production platforms must be built some miles offshore, in roughly 40 m of water. This is not a great depth, and would present no new problems were it not that the sea freezes in winter to a depth of around 2 m. Wind blowing across the surface of the ice sheet causes it to move at speeds up to 1 m s pressing it against the structure. Ice is... 

Fig. 28.9. Two alternative designs for oil production platforms in ice-covered sea a monopod and an artificial island.

A large number of parameters are involved in the choice of the corrosion protection system and the provision of the proteetion eurrent these are deseribed elsewhere (see Chapters 6 and 17). In partieular, for new locations of fixed production platforms, a knowledge of, for example, water temperature, oxygen content, conductivity, flow rate, chemical composition, biological activity, and abrasion by sand is useful. Measurements must be carried out at the sea location over a long period, so that an increased margin of safety can be calculated. 

Production platforms are coated only in exceptional cases or for the purposes of investigation because the life of the structure is greater than the life of the coating. Therefore in the design of the cathodic protection, only the protection potential Us of the steel need be considered. Steels with an ultimate tensile strength of up to 350 N mm are used for these structures, which are weldable even in thick sections, and the hardness of the welded material can be kept to 350 HV (see Section 2.3.4 [2,10]). Aluminum anodes with the same protection effect and life as zinc anodes have much less weight. This is a very important advantage for... 

The distance between the structure and fixed impressed current anodes is an important factor. The number of anodes has to be small so the anodes need to be relatively large, which will result in too negative a potential if the distance is not sufficiently great. A minimum distance of 1.5 m is prescribed [1-3], but this involves considerable construction effort due to the effects of heavy seas. Besides the so-called restriction on impressed current installations, there is the requirement that the corrosion protection be switched off when diving work is being carried out [14]. This regulation is not justifiable. Work on the underwater region of production platforms takes place continuously, as far as the weather allows if the protection must be switched off each time, the impressed current protection becomes very limited. 

The ASME code requires every pressure vessel that can be blocked in to have a relief valve to alleviate pressure build up due to thermal expan sion of trapped gases or liquids. In addition, the American Petroleum Institute Recommended Practice (API RP) 14C, Analysis, Design, Installation and Testing of Basic Surface Safety Systems on Offshore Production Platforms, recommends that relief valves be installed at vari ous locations in the production system and API RP 520, Design and Installation of Pressure Relieving Systems in Refineries, recommends various conditions for sizing relief valves. 

This analysis forms the basis of a widely used industry consensus standard, American Petroleum Institute, Recommended Practice 14C, Analysis, Design, Installation, and Testing of Basic Surface Systems for Ofi- i orc Production Platforms (RP14C), which contains a procedure tor dcicnniniiig required process safety devices and shutdowns. The procedures ilescribed here can be used to develop checklists for devices not covered by RP14C or to modify the consensus checklists presented in RP14C in areas of the world where RPI4C is not mandated. 

Based on the information contained in these figures it is possible to draw an area classification diagram of the facility. Figure 17-15 shows an example for a typical offshore production platform. 

Figure 17-15. Hazardous area location diogram for a typical offshore production platform.

RP 14F Recommended Practice for Design and Installation of Electrical Systems for Offshore Production Platforms RP. 500 Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified As Class I, Division 1 and Division 2. 

Vickers, K. and Knittel, T. no date. Detonation Arresters for Offshore Production Platforms. Paper presented to API Task Force for API RP I4C. Westecli Industrial Limited, Calgary, Alberta, Canada. 

In an offshore oil production platform, a major accident occurred partly because pump seals failed and therefore an antifoaming agent was not delivered to a crude oil separator. The fact that the pump seals were defective should have been picked up during routine inspections, but the inspections were neglected because of production pressures. The failure to carry out the inspections was a latent error. 

FIGURE 2.10 TRIPOD Failure-State Profiles of Two Production Platforms (Wagenaar, 1992). 

Gas production platform under construction in the Gulf of Thailand. (Corbis-Bettmann)... 

FPN No. 5) For further information on electrical system for hazardous (classified) locations on offshore oil and gas platforms, see Design and Installation of Electrical Systems for Offshore Production Platforms, ANSl/APl RP 14F-1991. 

API Recommended Practice 14E, Fifth Edition Recommended Practice for Design and Installation of Offshore Production Platform Piping Systems, October 1991. 

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