The new surge in drilling for coalbed methane gas has increased the need for quantitatively defining the grade of the various coal seams. The most common measurement for grading the coal seams has been through the use of formation bulk density. Empirical algorithms have been developed which use the formation bulk density to rank coal in terms of proximate analysis. Such empirical analysis has also made use of the Litlio-Density (LDT*) with its Photo Electric Factor (PEF), neutron, and resistivity measurements in recent years. New methods need to be developed that do not depend on empirically derived algorithms so that the coal grading analysis can be significantly improved.
The addition of data from the Geochemical Logging Tool (GLT*) to a LDT/CNL (Compensated Neutron Log) and resistivity logging suite offers such an opportunity. The GLT measures natural activation and prompt neutron capture gamma rays from which it produces measurements of the most abundant, and a few trace inorganic elements. This paper illustrates the need for development of a coal ranking and grading model based on the elemental analysis. For proper application of the model, it is necessary for it to be calibrated to core measurements (ie. rank of the coals).