Geological processes that control lateral and vertical variability in coal seam moisture contents—Latrobe Valley (Gippsland Basin) Australia

Abstract

A study throughout the Latrobe Valley coal measures of coal moisture distribution using downhole bore data and 3D digital models of large bore data sets indicates lateral and vertical moisture variability is controlled by a number of factors. These include burial, type of overburden, age of the seam, marine influence, coal lithotype and lateral compression on folds and monoclines. The same rules appear to apply to the adjacent Alberton coal measures in the south Gippsland Basin, suggesting these factors may be widespread in other brown coal basins where moisture contents are still equilibrating through differential compaction. In Gippsland average moisture down seam decreases by 1–2% per seam and at a rate of approximately 1% every 20 m. Weight average moisture content for each seam decreases on average at a rate of 0.5% every 1 million years. A stepwise decrease in moisture content between the ∼100 m thick major seams of 1–7% reflects large intervals of time are represented by the relatively thinner (1–10 m thick) interseam sediments. Compression by monoclinal folding can decrease moisture contents up to 7%. For any given depth, moisture content appears higher on anticlines due to a lowered intensity of compression than in adjacent synclines. It is considered likely that coals folded over anticlines are more fractured, thereby containing greater amounts of free water. Use of the lower moisture coals and monoclinal coals may be preferable for future power station developments. Despite an increase in overburden/coal ratios, there would be significant savings in a lowered coal volume to calorific value, and a consequent reduction in greenhouse gas emission.