The origins of dry gases: Bacteria, high maturity, or solubilisation/diffusion through shales

Conference · Sun Dec 31 04:00:00 EST 1995

OSTI ID:214814

Prinzhofer, A; Pernaton, E; Huc, A Y ^[1]

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1. IFP, Rueil-Malmaison (France); and others

Dry gas (C1/C1-C5 close to unity) occurrence is generally interpreted as bacterial, or thermogenic at high maturity level. The isotopic ratios of methane are considered as good discriminators of origins. Different observations and experiments give new clues to interpret some of these gas deposits: the movement of hydrocarbon gases through shales may be in some cases controlled by the solubilisation/diffusion of the gas molecules in the water. This induces important chemical and isotopic fractionations, the diffusing gas being highly enriched in methane, and isotopically lighter. Moreover, experimental pyrolyses of a type 2 kerogen indicates that, if it is possible to get a very dry gas with severe cracking conditions, the associated C2+ fraction, as it reacts like a residue, has extremely heavy isotopic signatures ({gamma}{sup 13} C{sub PDB}>0), never seen in natural gas. We can thus infer that some of the thermogenic gases become dry because of post-genetic chemical fractionations, leaving mainly the methane to concentrate in the reservoir.

• OSTI ID: 214814
• Report Number(s): CONF-950801--
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
58 GEOSCIENCES
BACTERIA
ISOTOPE RATIO
KEROGEN
METHANE
NATURAL GAS
NATURAL GAS DEPOSITS
ORIGIN
SHALES