CHARACTERIZATION OF GNEISS AND LIMESTONE ROCKS IN OGUN AND KWARA STATES, NIGERIA FOR PREDICTING DRILL COMPONENTS’ LIFE

Abstract

The study characterized selected rocks in Ilorin and Ibese areas, south western Nigeria for predicting drill components’ life. Two rock types namely gneiss and limestone were involved in the characterization and subsequent prediction of drill component life. Five (5) rock samples from each of the deposits (gneiss and limestone) were prepared and analyzed in the laboratory for chemical, physical and mechanical properties. Geological data such as dip, dip direction and joint spacing were taking using compass clinometer while global positioning system was used for their respective location. Some surface features were noted. The percentage chemical composition of rock samples was determined using x-ray fluorescence spectrometer. The results of the gneiss and limestone samples show that SiO2 and CaO content of the samples was 61.88 % and 52.3 % respectively. The average dry density of gneiss was 2.6 g/cm3 and limestone was 2.39 g/cm3. The average uniaxial compressive strength value for limestone and gneiss are 93.83 MPa and 195 MPa respectively classified as moderately strong rock and strong rock. The average tensile strength value for limestone and gneiss samples are 5.86 MPa and 11.68 MPa respectively classified as very high strength and extremely high strength. The average point load index value for limestone and gneiss samples are 3.91 MPa and 7.79 MPa respectively classified as very high strength. Selected parameters such as joint spacing, specific energy and uniaxial compressive was correlated with drill components’ (button bit, shank adaptor, coupling sleeves, and drill rod) to predict their lifetime using SPSS software. The model was used to develop a computer programme DRISOFT Version 1.0 using Visual Basic 6.0 to predict drill components’ life span in selected rocks (gneiss and limestone) when necessary inputs parameter supplied. The bit wear rate values ranged from 326.9 – 330.6 m/bit for gneiss and 212.5 – 216.4 m/bit for limestone. This indicates a very low lifetime due to very high wear rate. Also, the lifetime of other drill string components’ (shank adaptor, coupling sleeves, and drill rod) are about 10 times that of bit life.