Abstract
Six coal geomodels, constructed from μCT images of coal seam gas (CSG) samples from the Surat and Bowen basins, were analysed to identify percolation pathways and 3D flow simulations were conducted to predict permeability. This study has provided insights into the impact of cleat connectivity on permeability. As the models are representations of open cleat systems, the results provide an estimate of the full potential benefits of performing acidification treatments to remove calcite from previously cemented cleat flow channels.
A commercially-available simulation package was used for both flow simulations/permeability predictions and flow path analyses. Cleat connectivity, with respect to each flow direction, was determined by identifying the percolation path(s) and, consequently, tortuosity (τ) and percolation path apertures (PPA). The main flow path τ and PPA for each flow direction per geomodel is then assessed against the predicted 3D permeability of the compressed version of the geomodel. Results show that the predicted lateral permeability for Surat geomodels are lower than the Bowen models. While this finding holds true for these samples, it must be noted that there is a large variability in permeability across both basins.
The 3D simulations also indicated preferential flows along the face cleats for lateral direction (X and Y axes in digital space). The exception is when a master cleat traverses along the same direction as the butt cleats. In general, we found the predicted k of the geomodels correlated to cleat connectivity as a function of τ and PPA. That is k is directly proportional to PPA whilst inversely proportional to τ, with the PPA better correlated to k. Whilst the findings in this research provides insights into cleat connectivity and its impact on permeability, further research is warranted. A combined experimental and computational approach covering larger spread of samples (i.e., multiple wells, depths and basins) is recommended.
