This study is an evaluation of drilling mechanisms for widening drilling operations, which are also called hole opening or enlarge drilling operations, in hard rock formations during drilling operation with fixed cutter bits. This paper focuses on correlating drilling performance, or Rate of Penetration (ROP), with drilling parameters such as Weight on Bit (WOB), rotary speed, Torque on Bit (TOB) and bit type. Laboratory Drill-Off Tests (DOT) were conducted using a drilling simulator. Natural granite specimens were penetrated using different types of fixed cutter bits with different diameters. Various magnitudes of WOB were applied during these drilling experiments in order to study drilling performance in this type of formation. A well-organized drilling experimental plan was proposed to cover both procedures of pilot holes and widening drilling operations. Comparison were made between performance conditions obtained during the drilling operations of pilot holes and similar conditions during widening drilling operations. Furthermore, bit-rock interaction was studied by comparing experimental data with that obtained from empirical models. The focus of this paper was to analyze the ROP during each stage of the widening drilling operations of a pilot hole and its correlation with other parameters. The applicability of current empirical models and their limitations in widening drilling operations in hard rock formation was analyzed. In this way, this drilling model is applied in widening drilling operations of hard rock formation with fixed cutter bits.

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