Jida 4 is an overseas ultra-deep prospecting well completed by CNPC for important scientific research, with design depth of 6350m and completion depth of 6596m. Three formation pressures and drillability profiles of rocks are established by investigation to achieve optimized and fast drilling technology, including optimization of well bore structure, bit and drilling tool combination and improvement of drilling parameters; the developed salt-resistant and high-temperature resistant ultra-high density saturated salt water drilling fluid system may ensure indoor experimental density of 2.55g/cm1, temperature of 180°C, the highest in-situ density of 2.44g/cm3 and temperature of 163°C and safely drill 450m interval of KKC layer, so as to achieve hole cleaning and downhole safety; research and application of ultra-high density salt-resistant and high-temperature resistant slurry system and spacer fluid system may ensure slurry density of 2.48g/cm3 and spacer fluid density of 2.5g/cm3, so as to achieve safe cementing of deep well.

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