# Influence of Drilling Along Pilot Holes on Drilling Performance and Effective Rock Strength +
## 3 Results and Discussion
### Impact of Pre-Cored Holes on Drilling Performance  
We begin by examining the influence of pre-cored holes on drilling performance, comparing data obtained from pre-cored and un-pre-cored sections, repeated thrice. The analysis focuses on torque and Rate of Penetration (ROP) as key indicators of drilling efficiency. Table 4 compares the Rate of Penetration (ROP) between pre-cored and un-pre-cored sections of the rock sample under the same drilling conditions. The finding emphasizes a significant difference in drilling performance, where the ROP is consistently higher in the pre-cored sections than in the un-pre-cored sections. This result suggests that a pre-cored pilot hole significantly enhances drilling efficiency by reducing resistance at the bit-rock interface, which is an important feature of drilling performance: the torque difference between drilling the pre-cored and un-pre-cored sections. In particular, a different response to the drilling conditions in each scenario is suggested by the increased torque measured during the drilling of the top section (pre-cored h1) compared to the bottom section (un-pre-cored h1). Figure 6: Data of repeated drilling tests showing bit positions in pre-cored hole at single experiment with repetition h1, h2, h3. Traditionally, torque is an important indicator of drilling performance, providing insight into the design of the bit, conditions, and overall downhole drilling efficiency when considering the corresponding Rate of Penetration (ROP) data. However, it is important to remember that other drilling parameters--bit design, bit type, cutter type and orientation--and applied parameters remain constant in our research. Therefore, the structural distinctions between the pre-cored and un-pre-cored formations are the only reason for any variances in torque and Rate of Penetration (ROP). The discrepancy between torque and ROP suggests that the structural properties of the drilled formation have a major impact on drilling success. The structural properties of the drilled formation, such as rock strength, fracture density, and mineral composition, significantly impact drilling success due to their influence on bit-rock interactions. High-strength formations require greater energy for penetration, which can lead to increased torque and slower ROP. Conversely, pre-existing fractures or weaker material integrity in pre-cored formations reduce resistance, enhancing the Rate of Penetration (ROP) while introducing complexities in torque response. These structural differences dictate the Mechanical Specific Energy (MSE) required for drilling, affecting efficiency and tool wear. Understanding these properties is crucial for improving drilling strategies, as they govern how effectively the drill bit interacts with the rock. In addition to analyzing drilling parameters, such as Rate of Penetration (ROP) and torque, the Mechanical Specific Energy (MSE) is evaluated to measure the energy efficiency of our drilling process by using pilot holes. Inspired by [PERSON]'s seminal work in 1965, we utilized [PERSON]'s equation to calculate MSE (pilot holes) for our rotary drilling system. \[MSE=\frac{WOB}{(Aff-Aho)}+\frac{120\pi\cdot N\cdot T}{(Aff-Aho)*ROP} \tag{2}\]  
The Mechanical Specific Energy (MSE) was calculated by using Equation (2), which offers valuable information about the mechanical work required to excavate a unit volume of rock during drilling. [PERSON]'s equation enables a comprehensive assessment of energy efficiency in the drilling process. By including MSE analysis in our experiment, our objective was to improve our understanding of the energy efficiency of drilling operations. This enhanced the knowledge we obtained from traditional drilling parameters, like Rate of Penetration (ROP) and torque, by enabling us to assess the effectiveness and performance of our rotary drilling system from a wider angle. The Mechanical Specific Energy (MSE) values in Table 4 show the mechanical energy used in drilling for both pre-cored and un-pre-cored formations at 60 revolutions per minute.