Generation, Migration, and Accumulation of Hydrocarbons Indicated by Headspace Gas Analyses

Abstract

Headspace gases from 26 exploration wells drilled in Japanese oil and gas fields were analyzed.
Carbon isotope values and chemical compositions of gases can indicate the different origin of methane. A comparison of δ¹³C₁ and vitrinite reflectance values showed that a significant proportion of gases might have migrated from greater depth. Except for secondary fractionation in the reservoir, DST test gases have almost the same δ¹³C₁ values as those of headspace gases at the same depth.
The analytical results of headspace gas analyses widely differ in well to well. These results may reflect the influence of ganeration, migration, and accumulation of hydrocarbons in each area.