Use of temperature logs in coal seam gas reservoirs: Application to the Sydney Basin, Australia

• Temperature logs can be used as proxies for changes in gas content and composition.
• Coal seam gas content and composition often respond to hydrogeology, temperature and pressure changes.
• Wireline temperature logs are routinely utilized for monitoring water flow in reservoirs.
• Temperature logs respond to changes in water flow which is related to coal seam gas distribution.
• Temperature log gradients and profiles can be mapped spatially to identify gas zones and domains.

This study examines the relationship between borehole temperature logs and gas distribution in coal seams, both spatially and with depth. Temperature logs are often utilized in hydrogeology to monitor groundwater flow which can introduce methanogenic consortia into coal seams, resulting in the generation and accumulation of coal seam gases. Areas of hydraulic connectivity, characterized by open cleats and fractures, provide a pathway for the meteoric influx, whereas tight, mineralized sections of strata prohibit vertical flow and have the potential to trap coal seam gases, or to limit the influx of methanogens and the generation of secondary, biogenic methane. The combination of these concepts raises the possibility of utilizing temperature logs for mapping coal seam gas distributions and assisting exploration activities. Wireline temperature logs are inexpensive to obtain as part of any exploration, production or monitoring program, but provide information pertaining to flow regimes and in situ geological environments. A case study is presented from the Sydney Basin of Australia to demonstrate the types of analyses and interpretations relating to coal seam gas distribution that may be gleaned from temperature log datasets.