Computerized coal-quality prediction from digital geophysical logs

A digital suite of geophysical logs, including gamma-ray, resistivity and gamma-gamma density, were used to develop and test a method for predicting coal quality parameters for the Wyodak coal in the Powder River basin of Wyoming. The method was developed by plotting the average of various log response increments (obtained from the contractor's 9-track digital tapes) versus the analytically determined ash, moisture, and Btu/lb for the same intervals of the coal seam. Standard curve-fitting techniques were then employed to determine which log response parameter most accurately predicted the various quality parameters. A computer program was written that reads 9-track, digital, log tapes and determines the coal quality parameters based on the relationships between log response and analytical values. The computer program was written in Fortran 77 for a VAX 11/780 minicomputer. The program was designed to run interactively with user-determined options depending on which geophysical logs were available. Preliminary results have been very encouraging to date with predicted versus analytically determined parameters being estimated to an accuracy of +/-300 Btu/lb (with the average being +/-150 Btu/lb), +/-2% ash and +/-3% moisture. This compares to ASTM lab-to-lab analytical standards of +/-100 Btu/lb, +/-0.7% ash, and +/-0.5% moisture. This prediction methods ismore » applicable to coals from other basins and offers promise as a cost saving tool for exploration and production uses.« less