Production • Processing • Handling


Centralisers: keeping well casing and connections from snagging O


il tubular centralisers tend to get taken for granted while they are working correctly, deep down in the


well bore under enormous extremes of pressure and temperature. Until a centralisation problem happens to occurs, that is. The centraliser’s job is to keep the well casing and


its connections from snagging on the bore wall and at total depth to be tough enough to counteract the forces exerted by the tubular, to centralise it in the borehole allowing fluids and cements to move freely through the annulus. This is vital to centralisation, and good centralisation is critical for good cementation. Of all the applications a centraliser has to handle


the underreamed hole is the toughest. A fundamental problem with underreamed wells is getting effective casing centralisation in the underreamed section. Most bowspring centralisers will break if you leave


them to locate in a hole of diameter larger than the casing they have just passed through. To try to solve this


some manufacturers make them oversize to improve standoff down hole, which makes the centralisers so tight in the casing that they need a huge restart force to get them moving and which can prevent passage of the tubular to final depth.


Conventional bowspring centralisers that are wide


enough to fit the underreamed section get so seriously compressed in passing though the narrower casings that the bows lose their elasticity and cannot expand to the diameter of the underreamed hole. Solid centralisers do not break, but by definition


says Cenetek Ltd, they are inflexible and undersized in the open hole providing completely inadequate centralisation. The Centek S2 UR centraliser is made from a single


piece of heat-treated steel and can compress virtually flat to casing, traverse thousands of feet of previously set casing, yet once in the open hole it regains its original size and shape to provide the standoff required for effective centralisation.


Enter 38 or ✔ at www.engineerlive.com/iog


Centek Limited is based in Newton Abbot, Devon, UK. www.centekltd.co.uk


Offshore dehydration plant significantly reduces carbon emissions


P


rior to shipping to shore natural gas is often dried to prevent the formation of gas hydrates; flammable


waxy deposits which can block a high pressure pipeline. Drying offshore is achieved by passing gas through glycol and then regenerating that glycol by boiling off the absorbed water and recycling the glycol in a process loop.


Insufficient drying results in the risk of hydrates


and corrosion forming, while over drying burns up unnecessary amounts of fuel gas used to reboil the glycol or stripping gas. Glycol often fouls the flare burners so this methane rich stripping gas is sometimes vented, unburnt. Methane has a carbon footprint 22 times that of CO2


so any possible improvement is both


economically and environmentally a sound investment for any operator. A North Sea installation trialled an MCM heated


silicon sensor moisture sensing technology, in order to try to optimise the consumption of stripping gas flow by raising the water content closer to the gas export quality - whilst still remaining within contractual limits. The repeatability and accuracy of this sensor


outperformed the installations previous analysers, enabling the operator to reduce the metered ‘gas to flare’ value from a previous average of 1.7tonne/hour to 1.2tonne/hour. A significant saving is made of 30 per cent in ‘gas to


flare’ while comfortably maintaining gas export quality within the contractual specification. Half a ton/hour of stripping gas is equivalent of /hr or a 168tonnes a day. The difference


12tonnes of CO2


in water content is just 2ppmV. Enter 38A or ✔ at www.engineerlive.com/iog


Moisture Control & Measurement Ltd is based in Wetherby, West Yorkshire, England. www.mcm-moisture.com


38 www.engineerlive.com R


apid gas decompression (RGD), also known as explosive decompression (ED), is a major concern


to seals used in the oil and gas industry. RGD occurs, when high system pressure is released within a short period of time, causing absorbed gas to expand and potentially damaging elastomeric seals. This has severe consequences for operational reliability and profitable production. However, due to the flexibility and resilience of elastomers, their ability to self- energize and to compensate for housing tolerances, surface textures or scratches, elastomers are still the first choice of sealing material for applications in the oil and gas industry industry. SKF Economos has continued to develop its


portfolio of sealing materials such as H-ECOPUR (TPU) or different rubber-types like SKF Ecorubber-H (HNBR), SKF Ecorubber-2 (FKM), SKF Ecoperfluoro (FFKM) or SKF Ecoflas (TFE/P), which are suitable for a wide range of applications including subsea and surface trees, well completion and valves. For RGD – and sour gas resistance according to NORSOK M-710 Annex A, B or NACE TM0297 – special grades are available in different specifications. Sour gas and RGD-resistance for sealing application is one of the key factors to reduce maintenance and downtime costs and to increase process reliability.


Enter 38B or ✔ at www.engineerlive.com/iog


SKF Economos GmbH is based in Judenburg, Austria.www.economos.com


Certified sealing solutions for rapid gas decompression


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