Abstract: Well Nan 71, the first extended reach, highly-deviated, long open hole and dual bull's-eye well in Henan oilfield, has a drilled depth of 2024m borehole deviation 55°and displacement 883m. In viewing of the poor cementation and strong mud yield of the formations in this area a polymer drilling fluid with oil mixed is selected and the relevant technological measures are optimized. Field application show that this drilling fluid system has strong inhibitive, anti-caving and prop-carrying capabilities and good lubricity and can meet the requirements of highly-deviated well drilling.