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The paper presents an attempt to integrate the results of surface geochemical survey (“free gas” method) and soil magnetic susceptibility carried out in "Brzesko-Wojnicz" area, the SE part of Poland. The measurement profile is located at the border of two regional tectonic units: the central part of the Carpathian Foredeep and the Outer Carpathians. . The purpose of the article was to find out a relationship between different indicators of hydrocarbon microseepage, which can provide useful information, especially in petroleum prospecting. A total of 38 soil and soil gas samples were collected from 1.2 m depth below the surface. Maximum concentrations of CH4, total alkanes C2-C5, total alkenes C2-C4 in soil gas samples reached: 36.1 ppm, 0.95 ppm and 0.23 ppm, respectively. Very low values of magnetic susceptibility of soil ranged between 0.8 and 12.9 10-8 m³ /kg. Moreover, the results of hydrocarbon concentrations and magnetic susceptibility measurements of soil gas samples were presented in a linear plot and then integrated with seismic image. The method presented in this paper is a complementary one and its results allow to better understanding of the complexity of hydrocarbon migration mechanisms in the studied area. [ABSTRACT FROM AUTHOR]

Surface geochemical method is an important technique in petroleum exploration. The purpose of this method is to record and analyze the distribution of micro-concentration of gaseous hydrocarbons, which migrate from subsurface accumulations to the nearsurface zone. The paper presents the results of surface geochemical survey carried out in the area of the Mołodycz gas deposit of the Carpathian Foredeep. A soil-gas geochemical survey was carried out along the six sampling lines corresponding to the seismic section. A total of 192 soil gas samples were collected from 1.2 m depth below the surface and then analyzed chromatographically. The maximum concentration of CH4, total alkanes C2-C4, total alkenes C2-C4 reached: 369.1 ppm, 3.5 ppm and 4.6 ppm, respectively. Based on the concentrations measured in the soil gas the C2H6/C3H8 (C2/C3) ratio was calculated, which allowed to evaluate the character of deep hydrocarbon accumulations. The statistical parameters, histogram distribution and scatter-plots of ethane versus propane concentrations shown dominance signals characteristic for gas-condensate accumulations. Moreover, normalized and filtered values of the total alkanes C2-C4 concentrations were drawn against structural map of the gas horizon of the Miocene strata. Anomalous concentrations of total alkanes C2-C5 were found in 11 zones. These zones were the effect of the migration from sources located at various depths. Such a comparison demonstrated also that hydrocarbon accumulations can be expected outside the known contours of the gas deposit. Results of surface geochemical survey combined with the geological studies and geophysical surveys provide a valuable source of comprehensive information about the explored area and can be a new perspective for exploration in a hydrocarbon provinces. [ABSTRACT FROM AUTHOR]