Near surface manifestation of hydrocarbons in Proterozoic Bhima and Kaladgi Basins: Implications to hydrocarbon resource potential

• Published in: Journal of the Geological Society of India Vol. 76; no. 6; pp. 548 - 556
• Main Authors: Kalpana, M. S., Patil, D. J., Dayal, A. M., Raju, S. V.
• Format: Journal Article
• Language: English
• Published: India Springer-Verlag 01.12.2010; Springer Nature B.V
• Subjects: Adsorption; Earth and Environmental Science; Earth Sciences; Geochemistry; Geology; Hydrocarbons; Hydrogeology; Petroleum geology; Ratios; India; Kaladgi; Thermogenic; Bhima; Light gaseous hydrocarbons; Proterozoic; Adsorbed soil gas; Carbon isotopes
• ISSN: 0016-7622; 0974-6889
• DOI: 10.1007/s12594-010-0115-8

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. C 1 to C 4 (CH 4 , C 2 H 6 , C 3 H 8 , i-C 4 H 10 and n-C 4 H 10 ) in the near surface soils. The concentrations of C 1 and ΣC 2+ (C 2 H 6 +C 3 H 8 + i-C 4 H 10 + n-C 4 H 10 ) 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 C 1 /(C 2 +C 3 ) < 10 and C 3 /C 1 *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 C 1 and ΣC 2+ in the study areas illustrate C 1 and ΣC 2+ 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.