泡沫钻井水力参数优化方法研究

Study on method for optimizing hydraulic parameters in foam drilling

泡沫钻井在国内外已得到广泛应用,但关于水力参数优化设计的方法还未完善。基于多相流理论和携岩理论,通过理论计算和分析,总结出泡沫钻井水力参数优化设计方法,即通过临界气液比与井口回压线性关系确定最优气液比;通过不同井深下最低井底压力确定最优井口回压,结合最优气液比、最优井口回压、井底压力、岩屑浓度确定最优泡沫流速,最后根据最优泡沫流速确定最优注气流量和注液流量。实例计算了井眼直径为200 mm、钻杆外径为114.3 mm、井深为1 980 m、钻速为9m/h、18 m/h、27 m/h对应的最优水力参数。提出的优化方法对泡沫钻井水力参数优化有实际指导意义。

Foam drilling has been widely used both at home and abroad, but the method for optimized design of hydraulic param-eters has not been improved. This paper concluded the method for optimized design of hydraulic parameters for foam drilling based on multi-phase lfow theory and sand carrying theory, and through theoretical calculation and analysis. That is, to determine the optimum gas/liquid ratio through the linear relation between critical gas/liquid ratio and wellhead backpressure; to determine the optimum well-head backpressure through minimum bottom hole pressure in different depths;to determine the optimum foam lfow rate by combining the optimum gas/liquid ratio, optimum wellhead backpressure, bottom pressure and cuttings concentration;and ifnally to determine the optimum gas injection lfow rate and liquid injection lfow rate according to optimum foam lfow rate. Example calculations were con-ducted for optimum hydraulic parameters corresponding to 200 mm hole diameter, 114.3 mm out diameter of drill pipe, 1 980 m well depth and 9 m/h, 18 m/h and 27 m/h drilling rate. The optimized method presented in this paper has a practical guiding signiifcance for optimizing hydraulic parameters of foam drilling.