Publications

Coal holds gas in a fundamentally different way than non-carbon composed reservoirs. Moreover, coal beds are both the source and the reservoir for methane. Like conventional gas reservoirs gas in coal can be generated through purely burialtemperature processes (i.e. maturation), at a maturity level corresponding to the oil window (vitrinite reflectance ~0.55%) methane gas is generated from thermogenic processes. However, unlike conventional gas systems, substantial (and economically viable) gas can be generated from immature coal (vitrinite reflectance <,0.55%). This methane comes from biogenic processes, i.e. microbes generating methane through a fermentation process of the coal or reduction of CO2 into CH4. Most of Indonesians coalbed methane resources will be of biogenic origin. Because of the inherent physical differences as well as how the gas is generated and held, low rank coals and conventional gas reservoirs need to be approached quite differently in their assessment. For example, it is the gas adsorption capacity which is measured instead of (measured or calculated) porosity. This is because it is the surface area within the pores which is important rather than the pore volume itself. Gas charge is also measured but the rate of desorption of the gas from the coal plays an important role in understanding how the reservoir will respond once being produced. Since little is known of Indonesias coalbed methane resources, it crucial that the coal reservoir is assessed properly and that means using different techniques than what is normally used inconventional plays.