Calibration of downhole density logs-Benhar Lovells Flat sector, Kaitangata coalfield

To capitalise on the advantages of downhole logging techniques in coal quality determination, it is necessary to calibrate the LSD logs against chemical analyses of the coal. A cored calibration drillhole is used for this purpose. The core seams are divided into plies (samples) on the basis of electric log reponse and using regression analysis, a linear relationship is established between moisture ash and logged density. The regression equation is then used to prepare transparent overlays enabling the field geologists to read ash contents of coal quality blocks directly from the density traces.