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<p>The redevelopment of complex fault-block oilfields in the Southern Ordos Basin faces dual challenges of slim-wellholes (Φ120&#xa0;mm) and high curvature (build-up rate &gt; 57°/30&#xa0;m), where the passability of slim (Φ73&#xa0;mm) dual-bend screw drilling tools (1.5° + 3°) is particularly critical. Moving beyond traditional geometric or static analysis, this study establishes an innovative “casing-open hole” passability evaluation model that explicitly couples the effects of Weight on Bit (WOB) and borehole curvature, based on the beam-column theory and contact mechanics, while considering the unique constraints of slim tools. In the casing section, geometric constraints verified the feasibility of the tool’s passage with a maximum lower bend point displacement of 47.3&#xa0;mm inside Φ124.3&#xa0;mm casing. In the open-hole section, for curvature radii of 15–30&#xa0;m, the model quantifies the synergistic mechanism between WOB (1–3&#xa0;T) and curvature, revealing that passability is significantly more sensitive to curvature changes than to WOB variations. Results indicate the tool can pass through a 30&#xa0;m curvature radius under the full WOB range (1–3&#xa0;T), while the safe WOB threshold decreases to 1.8&#xa0;T at a 15&#xa0;m radius. Stress concentration factors reach 2.1–2.8, with a peak stress of 749.4 MPa at the lower bend. This study provides a critical bend angle formula and a drag-thrust balance criterion for optimizing tool running, offering a quantitative and more reliable design basis compared to conventional empirical methods for high-curvature sidetracking in the Southern Ordos Basin. Field applications demonstrated a substantial increase in successful running operations, validating the model’s superior predictive capability and practical value. The findings provide not only technical support for well redevelopment in this region but also a theoretical reference for drilling engineering under similar complex wellhole conditions.</p>

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A case study on the passability of slim dual bend screw drills in high curvature sidetracking through slim boreholes from the Southern Ordos Basin

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年12月10日

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  • Zhang Hui,
  • Liu Xugang,
  • Yu Zhanmiao,
  • Liu Jiaqin,
  • Wang Changhao,
  • Feng Qianwen,
  • Meng Shuan,
  • Li Shaojie

摘要

The redevelopment of complex fault-block oilfields in the Southern Ordos Basin faces dual challenges of slim-wellholes (Φ120 mm) and high curvature (build-up rate > 57°/30 m), where the passability of slim (Φ73 mm) dual-bend screw drilling tools (1.5° + 3°) is particularly critical. Moving beyond traditional geometric or static analysis, this study establishes an innovative “casing-open hole” passability evaluation model that explicitly couples the effects of Weight on Bit (WOB) and borehole curvature, based on the beam-column theory and contact mechanics, while considering the unique constraints of slim tools. In the casing section, geometric constraints verified the feasibility of the tool’s passage with a maximum lower bend point displacement of 47.3 mm inside Φ124.3 mm casing. In the open-hole section, for curvature radii of 15–30 m, the model quantifies the synergistic mechanism between WOB (1–3 T) and curvature, revealing that passability is significantly more sensitive to curvature changes than to WOB variations. Results indicate the tool can pass through a 30 m curvature radius under the full WOB range (1–3 T), while the safe WOB threshold decreases to 1.8 T at a 15 m radius. Stress concentration factors reach 2.1–2.8, with a peak stress of 749.4 MPa at the lower bend. This study provides a critical bend angle formula and a drag-thrust balance criterion for optimizing tool running, offering a quantitative and more reliable design basis compared to conventional empirical methods for high-curvature sidetracking in the Southern Ordos Basin. Field applications demonstrated a substantial increase in successful running operations, validating the model’s superior predictive capability and practical value. The findings provide not only technical support for well redevelopment in this region but also a theoretical reference for drilling engineering under similar complex wellhole conditions.