Abrasivity evaluation for wear prediction of button drill bits using geotechnical rock properties

Abstract

The current study investigates the wear life of button bits and rate of penetration (ROP) of rotary-percussive drilling machines by employing geotechnical rock properties. According to the research plan, three hydropower projects and six active mining quarries in Pakistan were included. The field work included recording of drill bit consumption (m/bit) and measurement of penetration rate (m/min) from the 11 selected rock units. A comprehensive laboratory testing plan on the collected rock units was carried out to include rock abrasivity assessment [CERCHAR (CAI), LCPC (ABR) and abrasion value steel (AVS) tests], NTNU/SINTEF drillability parameters [Sievers’ J-value (SJ), brittleness value (S20), Cutter Life Index™ (CLI) and Drilling Rate Index™ (DRI)] and physico-mechanical properties [uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), porosity (n), density (ρ), p wave velocity (Vp), Schmidt rebound hardness (SRH) and brittleness index (B3)]. Moreover, XRD analyses were performed to compute equivalent quartz content (EQC %), rock abrasivity index (RAI) and Vickers hardness number of rock (VHNR). The least square regression technique was employed to predict bit life from geotechnical rock properties. Dependence of ROP on geotechnical rock parameters was also discussed. Finally, two multiple linear regression models were also proposed for the estimation of bit life based on the included geotechnical rock properties. The developed multi-variable models were validated using the F-test statistical method. The correlations so developed are particularly proposed for rock engineers involved in rock drilling projects.