Abstract: The Nanpu #3 Structure in Jidong Oilfield has big reserves which are deeply buried. Deep and ultra-deep wells have been drilled in this area with high bottom hole temperatures and large horizontal displacements. A high temperature KCl drilling fluid, BH-KSM, was formulated for use in this area. BH-KSM remains stable at temperature up to 200℃, and has excellent inhibitive and sealing capacity, and tolerance to CO₂ contamination, essential for dealing with borehole instability, creep of formation at elevated temperatures, and contamination to drilling fluid by formation fluid in Nanpu #3 Structure. Technology for field application of the BH-KSM was engineered for maximum functioning of the mud. Field application of BH-KSM in 10 wells in the Nanpu #3 Structure showed that percent hole enlargement in the Dongying Formation, known for its being water sensitive and prone to collapse, was less than 7%, and the minimum of which being only 3.98%. The mud had stable rheology during drilling. HTHP filter loss can be kept under 12 mL. Cuttings over shale shakers were hard and had good integrity, illustrating good inhibition of the BH-KSM. Good carrying capacity of the mud resulted in satisfactory hole cleaning and increasing rate of penetration.