Gas Geochemistry as a Tool for Risk Reduction in Hydrocarbon Exploration

摘要

Geochemical characterization of gas seeps and natural gas produced from the subsurface reveals the origin of the gas. Two distinct processes generate gaseous hydrocarbons in a reservoir, bacterial activities during diagenesis and thermal cracking of petroleum precursors, which produce biogenic and thermogenic gases respectively. Whereas bacterial gas is mainly enriched in methane, thermogenic gases contain an abundance of higher hydrocarbons in varying proportions. Chemical composition and stable isotopic characteristics also give an insight into the association of the gas with a liquid hydrocarbon pool and its maturity. Study of a gas seep undertaken in the past from a tube well in Rahatgarh in MP, India, revealed its predominantly biogenic origin and a gas collected from Bengal basin well was characterized as thermal high maturity thermal gas based on their chemical composition and stable carbon isotopic signatures. Whereas bacterial gases reported from seeps and tube wells may be of commercial importance, associated wet gases produced from the subsurface may lead to a commercial discovery when integrated with other geological and geophysical data.