Process practice of ultra-small borehole short-radius barefoot sidetracking horizontal wells with coiled tubing

Coiled tubing short-radius casing sidetracking technology has achieved breakthroughs in engineering applications. However, barefoot sidetracking and directional drilling still face the following trajectory control bottlenecks: the lack of a coiled tubing barefoot sidetracking process, insufficient optimization of stabilization drilling tool combinations, and limited tool face control for measurement while drilling (MWD) in ultra-small boreholes. This study conducted an engineering test at a standard well site in the Jianghan Oilfield old district. Through barefoot sidetracking, directional deviation building, and horizontal section stabilization drilling using a slickline Ø60.3 mm coiled tubing in a Ø110 mm borehole, three key technical parameters were systematically verified:The deviation building characteristics and inclination increase control laws of a single-bend downhole motor (Ø89 mm, bend angle 2.5°) under conditions of ultra-thin cement plugs and short radius;The stabilization and inclination reduction performance of a micro-bend angle (0.75°) downhole motor; The synergistic control capability of a Ø42 mm MWD and a Ø79 mm indexing tool (a tool used to control the rotational angle of the downhole tool face) in a solid-free saturated salt cement slurry. Through the accumulation of engineering data from 211 m of barefoot drilling, three innovative processes were developed: The coiled tubing barefoot sidetracking process, the slickline MWD and control process, and the trajectory control process with a total angle change rate ≥28(°)/30 m. The data and experience from this practice provide a decision-making basis for the industrial application of ultra-small borehole coiled tubing short-radius sidetracking horizontal wells, effectively supporting the economic development of old oilfields.