EFFECT OF PDC BIT WEAR AND OPERATING PARAMETERS ON OIL-WELL DRILL-STRING DYNAMICS

Drill-string vibrations reduces the drilling performance, the bit wear negative effects on the drill-string dynamics is one of the elements which limit reaching the optimum drilling performance due to vibrations caused by the bit wear and other factors. To optimize the drilling parameters in order to reduce vibration related problems, real time analysis on the drill-string is needed. Due to extreme complexity of the vibration phenomenon it is difficult to construct a drill-string model which includes all types of vibrations thus this project presents a mathematical drill-string model which includes bit wear parameter or parameters in order to observe the impact that bit wear have on the drill-string dynamics. A parametric study is carried out to analyze the impact of operating parameter such as weight on bit (WOB) and rotary speed (RPM), other parameters which are related to bit wear such rock confined compressive strength and bit-specific coefficient of sliding were also studied, the parameters were tested using real field data. The study showed that increasing WOB increases stick/slip. However, increasing RPM seems to eliminate stick/slip. Relating CCS to bit wear allowed to observe the relationship between and stick/slip and was found that the severity of stick/slip increases as bit wear increases. The simulation results show similar trends as observed in the field. The simulation results show similar trends as observed in the field.