Drillability Evaluation and Sensitivity Analysis of the Fencheng Formation Strata in Maye Exploration Area

Abstract Predicting drillability ratings and selecting suitable drill bits are crucial for improving drilling efficiency. This investigation employed Principal Component Analysis (PCA) to normalize adjacent well logging parameters such as natural gamma, well diameter, natural potential, and others as influencing factors and established a mathematical model for the drillability ratings of hard rock formations. A sensitivity analysis of drilling parameters for the Fencheng Formation rocks revealed that sonic time difference, formation density, natural gamma, and resistivity were closely associated with drillability ratings. Empirical results showed that a multiple logarithmic linear regression approach accurately predicted drillability ratings for hard rock formations with over 95% precision compared to experimental values. The Fencheng Formation strata’s high hardness and abrasion resistance result in poor drillability (with ratings above 7.5), with rotational speed sensitivity found to be higher than drilling pressure sensitivity for expediting drilling in hard formations. For the “turbine + PDC bit” drill tool combination, it is recommended to use a drilling pressure of 40 - 80KN and a rotary table speed of 50 - 70r/min. High rotational speeds and low drilling pressures effectively reduce bit sticking effects, while using PDC bits with turbines reduces bit wear, improving the economic efficiency of drilling operations without sacrificing mechanical drilling speed.