engleski

Application of surface geochemistry survey in the HC exploration

Analysis of natural hydrocarbon micro seepage is sometimes used by the petroleum industry to assess the occurrence of mature source rocks in poorly explored basins. Various applications of the method have also sought to pinpoint the location of commercially viable subsurface accumulations of oil and gas. The aim of this study was to compare and contrast soil air results anomalies within two geographically distinct, underexplored areas in the Pannonian Basin of Croatia and Slovakia, and perform a controlled test to determine whether the soil gas readings were repeatable, and whether the gas compositions obtained were consistent with subsurface data. Soil air samples were collected at sampling intervals of approximately 100 and 600 meters from an average boring depth of 1 meter. A subset of the samples were obtained during seismic acquisition operations so that results could be correlated with subsurface structure. Gas components of the samples were measured by gas chromatography to discriminate C1 to C4 in a suspected oil-prone area of Croatia, and from C1 to C5 plus CO2 content in a suspected gas- prone survey area of Slovakia. Gas composition and concentrations of the analyzed Croatian samples indicate a thermogenic origin for all of the soil gases, and infer the presence of mature source rocks in the subsurface. Gas concentration and composition anomalies suggest that their origin derives from subsurface micro seepage of both heavy and light oils. Occurrences of C1-C2-C3- C4 (-C5) distributions are most likely due to organic facies differences, maturity, thermogenic and biogenic mixtures as well as alteration processes such as biodegradation and water washing. In Slovakia, anomalous CO2 concentrations on surface are consistent with the presence of a known subsurface CO2 accumulation, hence this approach may also help delineate the risk of high CO2 concentrations. Multiple control samples were collected at various stations and analyzed in the laboratory by high resolution gas chromatography. Results confirm the reproducibility of the subject soil gas sampling method.

surface geochemistry, HC micro seepages, gas chromatography, soil gas anomaly

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