2007 年 72 巻 6 号 p. 585-593
Carbon isotope compositions of methane, ethane and propane, and hydrocarbon ratios in gas samples provide information of their origin (microbial vs. thermogenic), maturity of thermogenic component, compositional change due to migration, and extent of biodegradation. Mixing of gases with different origins or different maturities can also be evaluated using gas isotopic and molecular compositions. While these gas geochemical data have been used mainly for petroleum exploration, their applications for development, production and operation issues are also increasing. Headspace gas analyses can be used to delineate reservoir compartments and pay zones. Carbon isotope compositions in commingled production could be used to allocate contributions form individual production zones if isotopic differences exist between the gases from the contributing reservoirs. Origin of gas seepage in production sites could be investigated by the gas molecular and isotope compositions if enough reference data exist in the area.