Abstract
The isotopic composition of methane is primarily dependent on the stage of maturation of organic matter present in the hydrocarbon source rocks and is not changed during migration. The isotopic composition of in situ methane can be estimated from the maturity of the source organic matter. Migrated methane from deeper, more mature sources is recognized by its relative 13 C enrichment compared to indigenous methane. Examples are presented in this paper to evaluate the migration pattern of gases in sedimentary basins.