环空注气气举反循环钻井工艺及关键参数设计

利用气举反循环钻井技术解决长宁页岩气表层钻井漏失问题，需要解决常规气举反循环钻井技术井口敞开、井底压力控制不精确等问题。为此，在常规气举反循环钻井技术的基础上，设计了一种环空注气气举反循环钻井新工艺，新工艺加装旋转防喷器、钻杆旋塞等工具，具备井控能力。通过调节注气量、钻井液排量等关键施工参数，控制井底压力，减少钻井漏失。在多相流理论基础上，建立了与新工艺匹配的环空注气气举反循环井底压力计算模型，分析了关键施工参数对井底压力的影响规律，建立了关键参数设计方法，在安全窗口范围内优选关键施工参数，保证安全钻井。结果表明：井底压力随注气量的增大先减小、后增大，存在临界注气量；井底压力随井深增大而增大；井底压力随钻井液排量增大而增大。在长宁某井表层进行了现场试验，与同井段井漏地层相比，较常规钻井工艺技术井漏减少83.6%。研究成果为解决四川长宁页岩气表层井漏问题提供了一种新的技术措施。

Annular Aerated Gas-lift Reverse Circulation Drilling Technology and Key Parameters Design

Using gas lift reverse circulation drilling technology to solve the leakage problem of Changning shale gas surface drilling, it is necessary to solve the problems of conventional gas lift reverse circulation drilling technology, such as open wellhead and inaccurate bottom hole pressure control. Therefore, on the basis of conventional gas-lift reverse circulation drilling technology, a new annular aerated gas-lift reverse circulation drilling technology is designed. The new technology is equipped with rotary blowout preventer, drill pipe cock and other tools, which has well control ability. By adjusting key construction parameters such as gas injection rate and drilling fluid displacement, bottom hole pressure is controlled to reduce drilling leakage. Based on the multiphase flow theory, the calculation model of bottom hole pressure for annular aerated gas-lift reverse circulation drilling technology is established. The influence of key construction parameters on bottom hole pressure is analyzed, and the design method of key parameters is established. The key construction parameters are optimized within the scope of safety window to ensure safe drilling. The results show that the bottom hole pressure first decreases and then rises with the increase of gas injection rate, and there is a critical gas injection rate; the bottom hole pressure rises with the increase of well depth; the bottom hole pressure rises with the increase of drilling fluid displacement. The field test was carried out in the surface drilling of a well in Changning. Compared with the lost circulation formation in the same section, the lost circulation was reduced by 83.6% using the conventional drilling technology. The research results provide a new technical measure to solve the problem of lost circulation in the surface drilling of Changning shale gas in Sichuan.