Muhammad,

Conventional water based drilling muds depends so much on clay minerals like bentonite to carry out its functions. Unfortunately, this makes them vulnerable at greater depth as salinity and temperature continue to increase rapidly with corresponding increase in pressure. They can manage to sustain their functions till a temperature of about 185°F or even up to 200°F if effectively managed.

Oil based fluids are generally preferred in this kind of anomalous temperature zone because of their edge over water based muds (i.e. thermal stability, shale stability, lubrication, fluid loss control, etc). However, the huge environmental and financial effects that accompanies oil based mud has shifted the focus of most drilling firm to an enhanced water based mud which is less expensive and has minimal environmental concerns addressing all the existing shortfalls.

Unlike traditional water based fluids, high performance water based drilling fluid could accommodate temperature up to 300°F. Moreover, Galindo et al (2015) https://doi.org/10.2118/173773-MS worked on developing water based drilling mud that could tolerate up to 400°F as usually encountered in HP/HT reservoirs. It has being established that this enhancement can be achieved basically by replacing biopolymers contained in the conventional water based drilling mud with high temperature tolerant synthetic polymers .

I hope some of these information will help address your question.

Regards.

Olatunbosun Kafisanwo

The "maximum temperature limit for water-based drilling muds" is defined generally as "thermal and mechano-chemical stability of water-based drilling muds" at static (BST) or dynamic bottom hole temperature (DBT) for a given minimum time ( often ~ 16 h and more). Many service companies claim

high temperature and shear stabilities (marketing!), but be very careful and do your own roller oven tests.

The proven maximum application temperature of ecological, non-damaging and clay-free water-based drilling muds stands at about 180 - 200°C (special polymers, natural components and specific salts, i.e. Potassium Formiate).

Stability is the key here. If one is looking for a WBM system which will remain stabil to 140 C no problem. To stretch WBM's to 210 C you will require good product quality, high temperature polymers, formates, good solids control equipment, good fluids engineers (who really understand what they are doing), dilution space on site and deep pockets.