EVALUATION OF HYDROCARBON PROSPECTS USING SURFACE GEOCHEMICAL DATA WITH CONSTRAINTS FROM GEOLOGICAL AND GEOPHYSICAL OBSERVATIONS: SAURASHTRA BASIN, INDIA

D. Mani⁺*, D. J. Patil*, M. S.  Kalpana*  and  A. M. Dayal*

* National Geophysical Research Institute (CSIR), Uppal Road, Hyderabad 500007,  Andhra Pradesh, India.

⁺ Corresponding author, email: devleenatiwari@ngri.res.in

The Saurashtra Basin in western India is considered to have significant hydrocarbon potential. However conventional exploration methods, particularly for Mesozoic prospects, have been hampered by the thick basalt cover. In this study, near-surface geochemical methods are used to investigate the generation of thermogenic gaseous hydrocarbons in the basin. Shallow soil samples were collected from favourable locations identified by integrated geophysical and geochemical studies. The compositional and isotopic signatures of adsorbed gaseous hydrocarbons (methane through pentane) together with soil iodine concentrations were used as surface indicators of petroleum micro-seepages. High concentrations of adsorbed thermogenic methane (C₁= 518 ppb) and ethane plus higher hydrocarbons (SC₂₊=977 ppb) along with iodine concentrations up to 68.5 ppm were observed. Total organic and inorganic carbon (TOC and TIC) measurements, fluorescence and X-ray diffraction (XRD) studies showed that the near-surface hydrocarbon occurrences were seepage related. Elevated hydrocarbon and iodine concentrations were coincident with dykes and lineaments in the study area, which probably served as conduits for the micro-seepage of hydrocarbons.

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