Innovative drilling-fluid design for an HP/HT well

Drilling in the Qiongdongnan basin offshore China often has resulted in failure to reach desired objectives. Bottomhole temperatures as high as 475°F and pressures requiring mud weights as great as 19.5 lbm/gal severely limit drilling fluid performance and often contribute to failure to achieve desired, drilling objectives. Well Yacheng 21-1-4 was drilled in this basin with a semisubmersible rig. After total depth (TD) was reached, logs were run to bottom without incident with no significant drilling fluid related problems. This success is attributed to innovative, fit-for-purpose drilling fluids, and rigorous prewell planning over a 2-year period before drilling began. The full-length paper describes the holistic approach to drilling-fluid engineering for extreme well conditions.