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Authors
Affiliations
1 National Geophysical Research Institute (Council of Scientific and Industrial Research), Uppal Road, Hyderabad - 500 606, IN
2 Directorate General of Hydrocarbons, Noida - 201 301, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 76, No 6 (2010), Pagination: 548-556
Abstract
Reconnaissance surface geochemical survey for adsorbed soil gas analysis conducted in Proterozoic Bhima and Kaladgi Basins, have revealed occurrence of anomalous concentrations of light gaseous hydrocarbons i.e. C1 to C4 (CH4, C2H6, C3H8, i-C4H10 and n-C4H10) in the near surface soils. The concentrations of C1 and ΣC2+(C2H6+C3H8+ i-C4H10+ n-C4H10) in Bhima and Kaladgi Basins are in the range of 1-2594 ppb and 1 to 57 ppb and 1-1142 ppb and 1-490 ppb, respectively. The carbon isotopic data of adsorbed soil gas methane in few selected samples are in the range of -29.9 to -39‰ (PDB). The evaluation of adsorbed soil gas data indicates that all the gas components are cogenetic and hydrocarbon ratios of C1/(C2+C3) < 10 and C3/C1*1000 between 60-500 and 20-60 suggest that the adsorbed gases are derived from oil and gas-condensate zones. The carbon isotopic values of methane further support thermogenic origin of these migrated gases. The concentration distribution of C1 and ΣC2+ in the study areas illustrate C1 and ΣC2+ anomalies near Katamadevarhalli, Andola and Talikota in Bhima Basin and near Kaladgi, Lokapur and north of Mudhol in Kaladgi Basin. The hydrocarbon anomalies near the surface coincide with the favourable subsurface structural features and correlate with existing geochemical and geophysical data in these basins suggesting seepage related anomalies.
Keywords
Proterozoic, Adsorbed Soil Gas, Light Gaseous Hydrocarbons, Carbon Isotopes, Thermogenic, Bhima, Kaladgi.
