Vibration monitoring at drill-bit and its correlation with downhole mechanical specific energy (MSE)

Drill-bit vibrations are a part of rock fracturing and breaking in the drilling process, are potentially harmful to equipment, yet provide valuable insights about drilling dynamics and formation properties. Mechanical Specific Energy (MSE) estimates the mechanical energy needed to break up a specific amount of rock under ideal drilling conditions, while strain energy density (SED) measures rock energy per unit volume. Because both are energy-standardized measures, meaningful correlation can be drawn to ascertain litho-mechanical behavior. Here, the relationship between accelerometer-recorded downhole bit vibration due to bit-rock interaction, logging parameters, and MSE is examined. This approach integrates the bit vibration dynamics acquired through an 8.5-inch PDC bit, with logging data and SED of the formation, perceiving that minimal MSE should approach SED and is rock-type dependent. Spearman correlations show a strong positive association between axial vibration (accelerometer Y-component; 0.75) and MSE, in comparison to moderate links with lateral and torsional vibrations. Axial vibration, therefore, appears most sensitive to energy delivery efficiency at the cutting interface. We also observe weak positive correlations between MSE and deep and shallow resistivity (0.32), and moderate correlations with lateral (0.47) and torsional (0.49) vibration components. These interdependencies can reveal real-time formation evaluation if proper planning is made to get the data in real time, along with gamma through mud pulse telemetry. Thus, vibration-based monitoring systems are practically helpful in locating rock heterogeneity and can provide useful information for real-time geosteering, timely drilling adjustments, and while drilling reservoir characterisation.