EoW March 2010

technical article

3.2.2 Water-based and oil-based drilling muds Water-based systems Divalent cations such as cal- cium and magnesium, added to a freshwater drilling mud, inhibit clay formation and shale swelling. High levels of soluble calcium are used to control sloughing shale and hole enlargement, and to prevent equipment damage. Calcium-treated muds resist salt and anhydrite contami- nation but are susceptible to gelation and solidification at These are based on water-in- oil emulsions, typically with calcium chloride brine as the emulsified phase and oil as the continuous phase. They may contain up to 50% brine in the liquid phase. Invert emulsion muds are a ‘relaxed’ emulsion, with lower electrical stabilities high temperatures [9] . Oil-based systems

ensure the maximum efficiency (minimum downtime and maintenance) of oil and gas production and refining tasks of these installations. Extremely low temperatures (–40°C and –50°C) are common in this kind of environment and therefore it is important to use materials with a low glass transition temperature that ensures mobility of polymer chains at lower energy levels. The mobility of polymer segments in a wide operating temperature range reduces the crystallisation risk and the hardening effect on the polymer. This can be expected in fixed cables for platforms located in regions with harsh environments. The tensile strength (elongation at break) of these compounds has been measured at –40°C and –50°C, as can be observed in Figure 6 . Therban® LT 2007 based compound undoubtedly shows the best performance at –40°C and –50°C (highest elongation at break) followed by the compound based on Therban® LT 2007 and Levapren® 500 HV (prepared with Geniosil® XL 33), a combination of plasticisers (TOTM and DOS) and a combination of different specific surface (BET) aluminium trihydroxides (Apyral ® 120E and SM 200). Effect of coupling agents The high reactivity of an alpha-silane, such as Geniosil ® XL 33, may have contributed to improve the level of polymer and filler interaction and in this way ensure a good balance of mechanical properties and lower crosslinking density. Alpha-silanes are inherently more reactive than standard silanes; this means a higher level of hydrophobation of the ATH could have

Weight/IRMOil902/168h@100ºC Volume/Oil IRM902/168h@100ºC Weight/IRMOil 903/168h@100ºC Volume/Oil IRM903/168h@100ºC

Figure 2 ▲ ▲ : Variation of volume and weight after immersion in oil IRM 902 and 903 for 168 hours at 100°C

Figure 3 ▲ ▲ : Variation of tensile strength properties after immersion in oil IRM 902 and 903 for 168 hours at 100°C

and higher fluid-loss values [9] . The effect on weight, volume and variation of tensile properties can be observed in Figures 4 and 5 . Compounds based on Therban LT 2007 and Levapren 700 HV displayed the best performance and retention of properties. It is important to select materials with a high degree of polarity as polarity of the compounds plays a key role in oil resistance performance.

3.2 Media Resistance 3.2.1 IRM oil 902 and 903

Oil resistance is closely related to the polarity of an elastomer. The polarity of EVM elastomers is determined by the vinyl acetate content and for HNBR elastomers by the acrylonitrile content [5] . The measure- ment of properties and volume change after immersion in oil confirms this effect ( Figures 2 and 3 ). Compounds based on EVM 70% VA content and HNBR LT displayed the lowest swelling and variation of tensile strength property performance. This could be attributed to the high polarity generated by a high content of VA in the EVM polymer (70%) whilst in the case of the HNBR material, the polarity is inherent in the high dipole-dipole effect of the ACN group which, despite the low content in Therban LT 2007, is sufficient to provide the necessary oil resistance demanded for these compounds. The biggest variation of tensile properties can be observed in compounds based on EVM 50% VA content. The polarity of this compound is only good enough to withstand immersion in oil IRM 902 but not oil IRM 903 which is more aggressive and polar than 902. EVM 70% VA content compounds showed comparable oil resistance to HNBR based compound ( Figures 2 and 3 ).

Figure 4 ▼ ▼ : Weight and volume variation after immersion in brine and Carbo Sea drilling mud for 1,344 hours at 70°C

In the case of compounds based on polymer blends, there seems to be some synergy between HNBR and EVM polymers – if extreme physical performance is demanded EVM can be blended with HNBR. This contributes to the reduction of overall compound cost and improves processing while maintaining heat and oil resistance. Blends of HNBR and EVM have been previously developed to meet very demanding specifications, especially in military naval technology specifications, NES 518 (Def-Stand 61-31 part 12) and VG 95218 [10] . 3.3 Low temperature properties The flexibility of cables for offshore platforms in Arctic regions is fundamental to

WeightBrine (CaBr2)/1344h@70ºC VolumeBrine (CaBr2)/1344h@70ºC WeightCarboSea/1344h@70ºC VolumeCarboSea/1344h@70ºC

Figure 5 ▼ ▼ : Variation of tensile strength properties after immersion in brine and Carbo Sea drilling mud for 1,344 hours at 70°C

DeltaTSBrine (CaBr2)/1344h@70ºC DeltaEBBrine (CaBr2)/1344h@70ºC DeltaTSCarboSea/1344h@70ºC DeltaEBCarboSea/1344h@70ºC

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EuroWire – March 2010