Risk assessment of packed holeassembliesfor rotary well drilling

The main elements of the statistical model of packed hole assemblies (PHA) design for drilling holding sections in conditions of information uncertainty are formalized and described. A constraint system has been given for the angle maintenance conditions of wellbore direction and dynamic stability of bottom hole assembly (BHA) lateral vibrations. The influence of the information uncertainty of some factors (angle, parameters of the drilling practice, presence of local caverns, etc.) on risk indicators has been analyzed according to the results of the numerical calculations. It has been determined that the risks of angle maintenance disturbance are significantly influenced by the angle and weight on the bit (WOB), and dynamic stability conditions, such as angle and rotation frequency. Risks of multi-supported BHAs which have been designed for conditions of minimizing bit side force, dynamic stability and include 4-6 stabilizers.