Viscosifiers of water based drilling fluids have a very important role to support hole cleaning by a good yield point; but at elevated bottom hole temperature (more than 250°C, 482 °F); this polymer may undergoes thermal degradation which leads to reduce the yield point and poor hole cleaning.
Dear Ashkan
Thanks a lot for your answer;but I didn't mean by this question the Clay minerals viscosifiers which include the following principal clays :
• Kaolinites
• Illites
• Chlorites
• Smectites
• Attapulgite and Sepiolite
The clay minerals viscosifiers are usually used in the surface hole as Spud mud or as viscous sweep pill while drilling. Attapulgite (Salt water Clay)and sepiolite, are used in special situations in which montmorillonite (Bentonite) will not perform. These clays differ in structure from the more common clays in that they are elongated rod-shaped particles. Since these clays are shear dependent,they are as effective in saltwater as in freshwater. Sepiolite has the added advantage of being very temperature stable.
Hydroxyethylcellulose (HEC) -is formed by causticizing cellulose and reacting it with ethyleneoxide which replaces one or more of the hydroxyl groups present on the cellulose molecule. HEC imparts high viscosity to water or brines but exhibits no gel strengths. It is susceptible to degradation through shear or heat and has a maximum thermal stability of about 225°F. So it used mainly for workover and completion fluids.
I meant by this question a polymer viscosifier e.g. PYRO-VIS (sold by Milpark) is a sugar beet extract which acts as a supplemental viscosifier to increase
carrying capacity without the addition of bentonite.
Also Xanthan Gum biopolymer which is a product of the action of a bacteria (Xanthomonas Campestris) on sugar. This material may be used in a variety of brines and salinity levels. Xanthan gum begins to degrade thermally at temperatures of about 250°F. So; I asked for another polymer act as viscosifier for drilling fluid has a thermal stability up to 500 °F.
Kind Regards,
Ayman AL-Zahry
Dear Oyin Dina
Thanks a lot for your answer;but Driscal -D and Drestemp from Drilling Specialties Chemical Co. are mainly used as Fluid loss reducer not a viscosifier. I really tried to use these products with Xanthan Gum but the mud still unstable at 500 °F.
Kind Regards,
Ayman AL-Zahry
There's been a bit of work on cellulose materials such as microfibrillated cellulose. Data exists to show they are capable of stabilising fluids to higher temperatures than that possible with Xanthan gum. The other options usually involve sulphonated co-polymers but the low shear viscosity is never comparable to that found with bentonite or Xanthan gum.
