Key Drilling Technologies for Ultra-Deep Well Zheng 10 in Junggar Basin

The strata below the Qingshuihe Formation in the Junggar Basin are found with high uncertainty,low drillability and complicated pressure system,which severely restrains the progress of exploration and development by deep exploration wells in the lower-assemblage reservoirs.Therefore,the challenges in drilling deep layers in Well Zheng 10 were analyzed,and the key technologies were discussed,including optimization of casing program,development of special-shaped-cutter PDC bit,high-efficiency wellbore-stabilizing drilling fluid system and constant-bottomhole-pressure drilling.The results show that,the package of technologies for deep exploration wells in the lower-assemblage reservoir enabled Well Zheng 10 to record the largest well depth(7 802 m)in the Junggar Basin.The combination of the ridged-cutter PDC bit and the durable positive displacement motor(PDM)with uniform wall thickness has allowed an enhanced rate of penetration(ROP)in deep layers of the Junggar Basin hinterland.The synthetic-based drilling fluid can effectively suppress wellbore chipping due to hydration swelling of water-sensitive strata induced by drilling fluid filtrate invasion,and it is preferred for avoiding wellbore instability and ensuring wellbore quality in target layers in central Junggar Basin.The research findings provide guidance for the enhancement of ROP and efficiency in complex ultra-deep well drilling.