Application of underbalanced drilling techniques in Chang 6 well in Raoyang sag

Underbalanced drilling is one of the approaches to discover and evaluate oil and gas resources accurately, especially to evaluate and develop oil and gas zones of low pressure and permeability. In view of the problems in the drilling of Chang 6 well, such as insufficient well information, poor drillability, deep drilling, and difficult construction, based on the optimization of well structure, drill bits, bottomhole assembly and drilling fluid system, underbalanced drilling techniques are applied and good results are obtained. Field application shows that the application of underbalanced drilling techniques may guarantee the timely and accurate discovery of oil and gas reservoirs, protect the reservoir effectively, enhance the drilling speed, shorten the drilling cycle, and lower the cost. It lays solid basis for the wide application of the techniques to Huabei Oilfield.