Measurement While Drilling Method for Estimating the Uniaxial Compressive Strength of Rocks Considering Frictional Dissipation Energy

Abstract

Relationships between drilling parameters and the uniaxial compressive strength (UCS) of rocks are typically established through measurement while drilling (MWD) by analyzing either drilling speed or specific energy. This study enhances the commonly utilized specific energy formula by considering the frictional dissipation energy of the drill bit, along with the initial thrust and torque exerted by the drilling machines. A novel specific energy index, ηp, optimized for rotary drilling applications, was introduced. The modified expressions significantly mitigate the impact of variations in drilling parameters on the specific energy. Employing the concept of a minimum specific energy coefficient, a model was developed that directly relates drilling parameters to the UCS of rocks. An iterative solution method for determining the minimum specific energy coefficient was provided. Extensive MWD tests on intact granite samples, conducted on a specially developed indoor drilling test platform, facilitated the calibration of the minimum specific energy coefficient. The model’s efficacy in UCS estimation was further validated through additional MWD tests on sandstone and limestone. For sandstone, the model’s estimated UCS showed a relative error (RE) ranging from 0.62% to 21.22%, a mean relative error of 11.7%, and a maximum absolute error of 9.75 MPa. Limestone tests revealed an RE range of 1.99%–12.86%, with absolute errors between 2.53 and 16.4 MPa. The UCSs of sandstone and limestone were estimated to lie between 39.65 and 55.71 MPa and 113.29 and 143.90 MPa, respectively, demonstrating close alignment with the results of uniaxial compressive strength tests and confirming the model’s accuracy and reliability for UCS prediction using MWD data.