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.