Abstract: Shale oil and gas development practices have shown that longer lateral length of horizontal well is favorable to enhance single-well controlled reserve and economic benefits. Comparing with the reservoir properties in the United States, the shale oil and gas reservoir burial depth in China is similar, but the lateral length of horizontal well is quite shorter. Drilling technology optimization and enhancing lateral length of horizontal well have become one of the technical difficulties in the unconventional hydrocarbon reservoirs in China at present. The key constraints for lateral length were analyzed by taking the ultra-long horizontal well in Jimsar shale oil reservoir as an example, including rated pump pressure, drilling fluid safety density window, drill string and casing buckling, etc. In addition, a pipe string friction-torque calculation model was derived for horizontal well. The wellbore trajectory and drilling tool combination were optimized and the technical conditions for avoiding drill-string and case buckling were researched based on the geology conditions of Well JHW00421 in Jimsar shale oil reservoir and the technical parameters of available drilling equipment. A drilling program was developed for a horizontal well with 3 500 m lateral length. The final measured depth of this well is 5 830 m and the lateral length is 3 100 m, which meet the drilling program design. This technology could provide certain technical reference for the implementation of ultra-long horizontal well in shale oil reservoir.

Key words: shale oil reservoir, ultra-long horizontal well, well trajectory, pipe-string buckling, Jimsar