When the bottom hole temperature (BHT) is over 356°F, polymers and sulfonated agents of fresh water based drilling fluid generally degrade or loss effect quickly. To address this problem, we developed a low cost formulation including extra high temperature (430°F) polymers with sulfonated agents for BHT under 390°F with 87.5 pcf mud weight. This drilling fluid formulation was lab tested to have the mud properties of PV 40 mPa.s, YP 12 Pa, HTHP (390°Fand 500psi) FL 12ml and lubricant factor 0.05. The mud formulation was field tested from 14,890 to 20,036 ft of SINOPEC XW-3 Well in Guangdong, China. The measured maximum static BHT was 410°Fwith actual minimum 69pcf mud weight used. The drilling operation was successfully conducted without a major problem in this well with this new designed drilling fluid even though loss was encountered in this section of well that forced the lowering of mud weight to 69 pcf. At the same time, we believe the formulation can be used similar condition when the BHT is between 356°Fand 390°Fwithin desired mud weight of 87.5pcf. The formula also can adjust and use high salinity ultra-deep HTHP well.

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