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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]

Light hydrocarbons migrate from the petroleum accumulations to the Earth's surface through faults, fractures and horizons with increased permeability. The occurrence of light hydrocarbons in the near-surface zone forms the basis for the surface geochemical methods. These methods are divided into two groups: direct and indirect. The paper presents the results of "free-gas" method (concentrations of light hydrocarbons and nonhydrocarbon components in the soil gas samples), and also values of pH and calcite content measured in the soil samples. The aim of this paper was to recognize zones of the highest hydrocarbon potential using direct and indirect surface geochemical methods. The studies were carried out along the AB profile within the Biecz Anticline located in the eastern part of the Polish Outer Carpathians. Concentrations of methane, total alkanes C2-C5, total alkenes C2-C4, H2 and CO2 varies in ranges: 1.50 - 9.82 ppm, b.d.l. - 0.347 ppm, b.d.l. - 0.181 ppm, b.d.l. - 621.2 ppm, 0.01 - 3.19 vol.%, respectively. Along the AB profile the values of pH change from 4.34 to 8.14, whereas the values of calcite content vary from 0.04 to 23.14 vol.%. The highest anomalous zone for methane, total alkanes C2-C5, total alkenes C2-C4 and H2 was determined above the anticline core. In this zone we also recorded inverted anomaly of pH, which values were below the calculated background level; whereas the values of calcite content were above the calculated background value. The second, lower anomalous zone for light hydrocarbons and hydrogen is located in the southern limb of the anticline, where the Strzeszyn gas deposit have been discovered. In this area we have observed high similarity between pH and total alkanes C2-C5 anomalies, but we have not noticed anomalous values for calcite content. In the zones where the intensity of hydrocarbons migration is high, the results obtained by the direct and indirect methods confirm the mutual connections between the concentrations of the light hydrocarbons and the values of pH and calcite content. Therefore, indirect method is a reliable supplement for direct method, and both of these surface geochemical methods may be helpful for hydrocarbon exploration. [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]

The paper presents the results of surface geochemical surveys carried out using "free gas method" in "Brzesko-Wojnicz" area in the SE part of the Poland. The surveys were conducted along 2 measurement profiles. A total of 341 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 reached: 27,1 vol.%., 45,3 ppm and 0,174 ppm, respectively. In total, in the analyzed area there are anomalous concentration of total C2-C5 alkanes (over 3σ above calculated background mean) in 121 measurement points, comprising 9 zones ranging from 200 m to a 2 kilometres. Calculated hydrocarbon ratios CH4/ΣC2-C5 (C1/ΣC2-C5) and C2H6/C3H8 (C2/C3) allow to define the presence of compositionally diversified, deep hydrocarbon accumulations. The statistical parameters and histogram distributions of the above-mentioned ratios show dominance of condensate-oil character of deep-seated sources with the presence, in some samples, of the effects of current biochemical processes. The highest number of anomalies of total alkanes C2-C5 was determined over the Wojnicz thrust slice, particularly in the area of significant increase in thickness of autochthonous miocene sediments. The Wojnicz thrust slice is bordered to the south by the Dębno thrust slice, over where a decay of anomalous indications of total alkanes C2-C5 was observed. Besides, the thrust fault zone of this thrust slice collectively with the marginal part of the Outer Carpathian may create barriers to the potential migration and microseepage of hydrocarbons from deeper miocene horizons and from flysch sediments. The conducted analysis indicates that the number and distribution of surface geochemical anomalies point to the possibility of the occurrence of deep-seated accumulations, but the penetration of gas ingredients to the surface is determined predominantly by the tectonics of the area. [ABSTRACT FROM AUTHOR]