SRK Consulting has undertaken many unconventional gas estimation projects in Australia plus China, USA, Canada, Botswana and South Africa. Our experience with projects indicates many potential pit falls in the estimation of both Resources and Reserves can lead to either overstating or underestimating potential. Geology is a significant control and the context of gas estimations is critical to ensure their delivery as economic Reserves. SRK Consulting has experience of coal seam gas (CSG/CBM) Reserve and Resource in most eastern Australian basins and we have observed that the impact of coal quality and depositional environments are commonly underestimated and some potential gas upside is not necessarily captured from other aspects associated with coal seam gas analysis. The coal seam environment is complex comprising fluvial deposition in upper to lower delta plain settings where the complex interaction of sedimentary deposition is compounded by variations relating to the original peat swamp environment. The nature of the peat-forming environment and the genesis of the contained methane in shallow CSG reservoirs often results in highly variable gas saturations. By understanding these processes and identifying the geological features responsible for high-frequency variations in gas contents, exploration can be better targeted. Individual coal seam reservoirs typically split and coalesce within hundreds of metres but seam characteristics such as ash content can also vary over similar distances. The thin nature of the CSG reservoir also provides the potential for common relatively small faults (<5 metres) to fully displace the coal seam and effectively compartmentalise the reservoir. It is important to have a good understanding of the origin of the methane and how it has been stored in the reservoir. SRK has undertaken several projects in the Surat Basin where shallow coals are often highly gas productive. Deeper coals can be significantly undersaturated resulting in lower gas contents and significant dewatering requirements to achieve first gas. Lack of meteoric influx due to geometry and permeability barriers can result in minimal biogenic gas enhancement resulting poor permeabilities that require lateral wells to achieve reasonable productivity. Download paper here