Detailed compositional analysis of hydrocarbons in soil gases above multi-horizon petroleum deposits – A case study from western Poland

摘要: Abstract A surface geochemical survey was carried on in an area with a cluster of petroleum deposits western Poland. The largest these accumulations is the Paproc-Cicha Gora dry gas deposit reservoired Rotliegend sediments. Other, similar are: Paproc field discovered top part Carboniferous formation and W, N, Nowy Tomyśl fields localized Zechstein Limestone reef structures. Moreover, gas-condensate Jastrzebsko oil were found at shallower depths, Main Dolomite formation. This paper aims to analyze variability composition distribution near-surface gaseous hydrocarbons relation hydrocarbon various stratigraphic units depths. occurrence CH 4 , its heavier homologues unsaturated measured 267 soil samples. sampling sites located along six lines (A–A, B–B, C–C, D–D, E–E F–F) 200 m spacing. Concentrations total alkanes (C 2 –C ) alkenes 3 reached maxima 0.26 vol.%, 5.32 ppm 5.88 ppm, respectively. Soil–gas than interpreted as being derived from subsurface accumulations. These compounds penetrated zone by means active passive microseepage. Source strength microseepage land (determined C H 6 /C ratio) not factor that substantially changes patterns anomalies. Analysis values 8 coefficients confirmed presence compositionally diversified, deep study revealed even small condensate produce very strong signatures, contrasting deposits. reason may be specific effect migration within existing system. Dolomite, which both source reservoir rock Fore-sudetic monocline, plays role “filter”, modifies flux gases ascending deep-seated reservoirs. As result such “filtering”, signature recorded indicates dominance oil–gas giving rise obviously incorrect interpretations. interpretations evidenced compositional analysis gases, did explicitly confirm existence (Paproc-Cicha field). On other hand, identified anomalies generally reflect outline this accumulation. It supports applicability surveys exploration Monocline. depth must taken into account interpretation data used for positioning seismically results project indicate obscure deeper