Abstract: 2-bore coalbed methane horizontal wellsare drilled with tubing in way of aerated underbalance drilling. The gas injection pressure is controlled by the vertical well, a variety of complications during drilling in coal bedscan not only be effectively resolved, but also there are many advantages, including stable gas injection and lower bottom hole under-pressure maintained. Here in this paper an injection parameter optimization design model for aerated underbalance drilling in coalbed methane horizontal wells are set up. The effects of different bottom hole pressure differences on the balance pressure limit, collapse pressure limit, cuttings carrying limit and gas-liquid flow window are evaluated. The study results show that the model is reliable and can be applied in aerated underbalanced drilling of horizontal wells in coal beds.

Key words: coalbed methane, aerated UBD, injection parameters, bottom hole pressure difference, cuttings carrying performance 

摘要：  煤层气水平井双井筒油管注气欠平衡钻井技术，通过直井控制不同的注气压力不仅能够有效解决煤 储层钻进时出现的多种复杂情况，同时还具有注气稳定、易维持较小欠压值等优点。文章建立了一套适合于煤层 气水平井充气欠平衡注入参数优化设计的数学模型，通过实例分析评价了不同井底压差对平衡压力限、坍塌压力 限、携岩能力限以及气液流量窗口的影响。利用该研究成果在 ＦＬ－Ｈ１６－Ｌ煤层气多分支水平井进行了现场试验， 试验结果表明，注入参数模型优化设计是可行的，可在煤层气水平井充气欠平衡钻井中进行推广和应用。

关键词:  , 煤层气, 充气欠平衡, 注入参数, 井底压差, 携岩能力