位于四川盆地东北部的元坝气田二叠系上统长兴组生物礁气藏埋藏深度介于6 300~7 200 m，气藏温度介于149~164 ℃，三叠系下统飞仙关组的地层压力介于118~120 MPa，硫化氢含量平均为4.64%、二氧化碳含量平均为5.72%，礁体间储层连通性较差、部分礁体天然气储量动用不充分。为了提高气藏最终采收率，利用原井眼侧钻沟通储层，以期高效动用剩余天然气储量；基于工程地质特征分析及前期钻探实践，研发形成了侧钻井眼井身结构优化设计、低密度抗高温易酸溶钻井液和超深小井眼轨迹控制配套技术，成功破解了该区上部三叠系下统嘉陵江组及飞仙关组与长兴组的地层压力系数差异大诱发漏失及喷漏同存复杂、嘉陵江组和飞仙关组发育膏盐岩诱发套变、低压力系数储层（压力系数为0.6）漏失风险高及储层保护难度大、小井眼轨迹控制难度大等难题。YB103-1H井的应用实践结果表明：①六开长兴组低压储层专层专打，既可以确保安全建井，又通过降低钻井液密度避免漏失而保护了储层；②低密度抗高温易酸溶钻井液技术能够达成稳定井壁和保护储层的目标；③钻具组合优化实现了轨迹控制和防卡钻的目标。结论认为，超深井小井眼侧钻关键技术不仅为该气田高效动用剩余天然气储量及提高气藏最终采收率提供了技术保障，而且也为后续超深井小井眼侧钻井的安全高效施工提供了技术参考。

In the Yuanba gas field of northeastern Sichuan Basin, the Upper Permian Changxing Formation biogenic reef gas reservoirs are buried at depths ranging from 6300 to 7200 m, with reservoir temperatures between 149 and 164 ℃. The Lower Triassic Feixianguan Formation exhibits formation pressures of 118-120 MPa, with average H₂S content of 4.64% and CO₂ content of 5.72%. The reefs are relatively poor in reservoir connectivity, leading to incomplete gas reserve producing in some reefs. In order to improve the ultimate recovery of the gas reservoirs, sidetracking through original wellbores is employed for reservoir connection to efficiently produce the remaining reserves. Based on the analysis of engineering geological characteristics and previous drilling practices, a set of key technologies has been developed, including the casing program optimization design of sidetracked hole, low-density high-temperature-resistant acid-soluble drilling fluid, and ultra-deep slim hole trajectory control. These technologies provide effective solutions to the problems such as the co-occurrence of leakage and blowout caused by significant difference in formation pressure coefficients between the Lower Triassic Jialingjiang-Feixianguan Formations and the Upper Permian Changxing Formation, casing deformation induced by the developed gypsum salt rocks in the Jialingjiang-Feixianguan Formations, high leakage risk in low-pressure coefficient reservoirs (with a pressure coefficient of 0.6) and the difficulty of reservoir protection, and hard trajectory control of slim holes. The application of the technologies to Well YB103-1H demonstrates that, (i) the sixth spud with specialized drilling techniques for the Changxing Formation low-pressure reservoirs enables a safe well construction and also reservoir protection by reducing drilling fluid density to avoid leakage; (ii) the low-density high-temperature-resistant acid-soluble drilling fluid achieves the dual objectives of wellbore stability and reservoir protection; and (iii) the optimization of bottomhole assembly (BHA) allows for both trajectory control and sticking prevention. It is concluded that the proposed key technologies for sidetracking of ultra-deep slim holes provide not only technical guarantee for efficiently producing remaining gas reserves and enhancing ultimate recovery in this gas field, but also references for subsequent safe and efficient operations of ultra-deep slim hole sidetracking.