Origins of hydrocarbons in the Geneva Basin: insights from oil, gas and source rock organic geochemistry

Abstract An extensive subsurface investigation evaluating the geothermal energy resources and underground thermal storage potential is being carried out in southwestern part of Swiss Molasse Basin around Geneva Canton. Among this process, evaluation petroleum source-rock type an important step to understand system responsible some oil gas shows at surface subsurface. This study provides a first appraisal risk encounter possible undesired occurrence hydrocarbons Basin. Upon numerous source-rocks mentioned systems North Alpine Foreland Basin, marine Type II Toarcian shales (Lias) terrigenous III Carboniferous coals have been sampled from wells characterized with Rock–Eval pyrolysis GC–MS analysis. The (known as Posidonia shales) are showing dominant organic matter composition component Jura region south basin. Its maturity (~ 0.7 VRr%) that currently generates depth. show slight lacustrine component, wet window below Two bitumen samples retrieved (Roulave stream) shallow borehole (Satigny) heavily biodegraded. Relative abundance regular steranes Roulave indicates origin matter. source Satigny supposedly same even though deeper source-rock, such Permian expelling region, can’t be discarded. oil-prone most likely bitumen. A pocket encountered well (Geneva Canton), was investigated for molecular stable isotopic composition. analyses indicated made mixture microbial (very low ? 13 C 1 ) thermogenic gas. ethane propane suggests overmature (> 1.6 or ~ 1.2 VRr%. seems only satisfying these constraints remains nevertheless limited given thickness across area does not pose high exploration. higher assigned depth where they reached generated large amount sealing Triassic evaporites. faults fractures cross-cutting entire stratigraphic succession basin certainly serve preferential migration pathways gas, explaining its presence levels Satigny.