Application Study And Personalized Design Of PDC Bits Under Complex Geological Condition

The complex properties for the formations in the Rongdong region of Changqing oil field were analyzed with core information and well logging data. Results demonstrate that the greatly different hardness, diverse hard intermediate layers and poor drillability of the formations mainly result in the difficulty for conventional PDC drilling bit to be effectively utilized in this region. Based on the analysis of premature failure of PDC bits in Changqing oil field, the failure mechanisms were systematically studied. Research on PDC bit design principles was conducted, and a new PDC bit design method adopting the dual-protection cutting structure with hardness-resistant intermediate layer was proposed, the anti-eddy property of which was realized by proper crown bit configuration design, appropriate blade positioning and force equilibrium optimized tooth distribution. Meanwhile, the PDC bit design method for directional drilling on the determination of the heights of inner cone and corona was brought forward based on the principle of zero drift tendency.On the basis of theoretical research, the relevant visible three-dimensional design calculator program was compiled. Aiming at the complex formations in the Rongdong region of Changqing oil field, specific design was conducted for PDC drilling bit, and four types of corresponding PDC bits were successfully produced. In correspondence with the application of PDC bit, the packed structure named four-to-one drilling facility, including the PDC bit, single curved screw, short drill collar and stabilizer, was proposed. Application practice shows that the drilling facility not only uses the sliding tenability of single curved screw, but realizes the stable orientation effect with the double-stabilizer stiff drilling structure. Moreover, the facility brings the faster penetration advantage of PDC drilling bit into full play, and meets the requirements of trace control for deviation resistance in vertical section, directional buildup, compound adjustment and angle holding in orientation stabilizing. Field tests were carried out with the four specifically designed PDC bits. The Anding and Zhiluo formation in the Rongdong region were successfully penetrated. Compared with local cone bit, the penetration rate and bit footage were both significantly improved. The developed PDC bits become a breakthrough for their application in Changqing oil field, and offer theoretical and technical support for the extensive application of PDC bits in Changqing oil field.