R.W.C.Brom and F.Driedonks
ABSTRACT
This paper is a review of log evaluation techniques for coal exploration as applied by Shell Companies operating in various parts of the world.
The new generation of logging tools is described in brief and various examples of qualitative and quantitative log interpretation are discussed.
Qualitative applications include coal seam identification and correlation, detection of igneous intrusions and their effect on coal, the determination of the general overburden lithology, and characterization of coal weathering.
Quantitative relationships between log data and coal quality parameters established from core data are usually valid for a particular depositional area only. The use of such log-versus-core correlations is often even limited to parts of a single coal field because of significant variations in coal type and rank. It is shown by examples, however, that in bituminous coal of low Moisture Content these variations can be recognized by applying a Neutron logging tool with a relatively short source-detector spacing (0.25 m). This differentiation enables the main coal quality parameters, i.e. Ash Content, Volatile Matter and Calorific Value, to be determined accurately from logs after calibration against core data.
Some research aspects are discussed, including Sulfur logging, the determination of Moisture Content in low-rank coals from electrical Resistivity, the relationship between the hardness/strength of coal-associated strata and their wireline log response.