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粘稠泡沫在对付大量水侵和有效改进岩屑携带能力方面的稳定性，进一步促进了欠平衡泡沫钻井的应用。泡沫品质是控制泡沫携带岩屑能力的一个重要参数，井底泡沫品质不应低于５３ ％ 。聚合物的加入增强了泡沫流体的稳定性、流变性和失水性。采用泡沫钻井，具有井眼清洗良好、减少流体分离、机械钻速高、井下不发生着火和爆炸等优点，降低了钻井成本。由于安全、井控和环境方面的原因，越来越多的地区将采用封闭循环欠平衡泡沫钻井系统。旋转控制头、四相分离器等装置是进行欠平衡泡沫钻井的关键设备。我国的欠平衡泡沫钻井较少。中原油田采用清水混气钻了一口毛８ 井，吐哈地区在恰１０２ 井进行了泡沫钻井试验。在成本意识日益增强的工业中，正不断寻找节约成本的方法以提高现有油气田的生产寿命，泡沫钻井技术将是可靠的选择。

UNDERBALANCED FOAM DRILLING TECHNOLOGY

The stability of viscous foam in dealing with large water invasion and effectively improving solids carrying capacity further promotes the application of underbalanced foam drilling.Foam quality is an important parameter to control the solids carrying capacity of foam and the quality of the foam in bottom hole should not be lower than 53%.Addition of polymer can improve the stability,rheologic property and fluid loss characteristics of the foam.Foam drilling has many advantages:good bottom hole cleaning,a decrease in fluid separation,high penetration rate and no occurring inflammation and explosion in borehole etc.,which can reduce the drilling cost.Closed circulation underbalanced foam drilling system will be adopted in more and more areas due to the reasons as the safety,well control and environment.Such devices as rotation controlled head and four phase separator etc.are the key ones for underbalanced foam drilling.The underbalanced foam drilling used in China is fairly few (well Mao 8 in Zhongyuan Oil Field was drilled by use of aerated water and a foam drilling test was carried out at well Qia 102 in Tuha region).In the field of industry in which cost consciousness is strengthening day by day,the way to reduce cost is being searched uninterruptedly to prolong the production period of the existing oil and gas fields,for which,foam drilling technology will be a reliable selection.