AVEVA World Magazine

AVEVA World Magazine 2015 #2

AVEVA World Magazine | Technology insights and customer successes with AVEVA software

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For safety reasons also, PDO needed to ensure that the Operations & Maintenance team worked with up-to-date information; decisions based on inaccurate information could endanger the plant and the engineers working within it. This is especially important for such technically challenging projects as the Harweel oilfield. Another constant challenge was to keep as-built drawings updated after modification work. 'You can't update something if you can't find it,' Mr Al Lawati, noted ruefully. 'It was also difficult to circulate certain types of information, especially information like 3D models and drawings, to all the various stakeholders in the organisation.' Harweel: no room for error Sulphur is a common by-product of deep oil & gas wells, usually in the form of hydrogen sulphide, an extremely corrosive and poisonous gas. Hydrocarbons with a hydrogen sulphide content above 500 parts per million (ppm) are known as sour reservoirs; in Oman such reservoirs, including the Al Noor, Birba and Harweel fields, are in the south of the country. At Harweel, the hydrogen sulphide is collected and pumped back into the well at extremely high pressure, around 500 bar. No manufacturer offers a compressor capable of pumping hydrogen sulphide at this pressure, so the compressor at Harweel is a purpose-built unit. This high pressure forces the gas to mix with the oil, making it less viscous, which increases the oil production rate, so there is a considerable financial incentive to overcome the technical challenges. Hydrogen sulphide would make short work of conventional steel piping, so at Harweel the flow lines are made from corrosion-resistant glass-reinforced epoxy (GRE). And to handle a pressure of 500 bar they have massively thick walls, some 40 cm thick. GRE pipes can only be made in straight lengths; bends must be made of corrosion-resistant alloys. Such specialised materials are expensive. A single 27-metre length of corrosion-resistant alloy pipe costs as much as a new Ferrari, so CAPEX costs are considerable. The alternative approach, adding chemicals to the gas to enable standard piping to be used, may save capital costs but increases operating costs, and requires highly effective supply chain management. Conventionally, valves and pipes are joined by flanges, which are potential sources of leaks. While this is not necessarily serious in a normal facility, at Harweel a single drop of this hazardous mixture presents a serious Health & Safety threat. To avoid this, the valves are actually welded into place, having first been lined with a special corrosion-resistant alloy to make them last longer – a first for the industry. Nevertheless, with 500-bar pressures to withstand, even welded joints are potential weak points, so a rigorous condition monitoring programme is essential and weld information must be both reliable and readily accessible. (continued)

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