Abstract
The presented study reports the geochemical investigation for hydrocarbon prospects in western and central regions of Deccan Syneclise to evaluate the near surface manifestations of hydrocarbons due to microseepage; identify the sources of light hydrocarbon gases and integrate the results with geophysical data to demarcate the prospective areas for hydrocarbons. The adsorbed soil gas analysis of soil samples from western and central regions show the presence of C1–C4 hydrocarbons with concentrations of C1 and C2+ varying from 2 to 626ppb, 0–261 ppb and 4–255ppb, 0–114ppb respectively. The propane oxidizing bacteria (POB) ranged between 1.0×102 and 2.65×105cfu/g of soil. The evaluation of compositional ratios of adsorbed soil gases indicates that the gas components are co-genetic and migrated from subsurface hydrocarbon accumulations/organic rich beds. The carbon isotopic compositions of adsorbed soil gas methane from western region of Deccan Syneclise range from −29.87 to −13.09‰ (VPDB) representing near surface oxidation of gases subsequent to migration and are derived from gas producing type III kerogen. The δ13C signatures of soil carbonates from central region of Deccan Syneclise falling in the range of −9.61 to −5.1‰ (VPDB) indicate diagenetic alteration of seeping hydrocarbon gases in the surface soils. The adsorbed light gaseous hydrocarbon, propane oxidizing bacteria and soil carbonate anomalies are representative of samples from Kopargaon, Shirdi, Rampur and Newasa in western region and Edlabad, Popetkheda and Khandwa in central regions of Deccan Syneclise. These anomalies are in good agreement with thick subtrappean Mesozoic sediments of up to 2km delineated by the magnetotelluric (MT) and gravity studies in Deccan Syneclise, which might have sourced the hydrocarbon gases. The anomalous areas are also associated with Barwani-Sukta, Tapti and Gaviligarh faults which might have provided migratory pathways for light gaseous hydrocarbons. The geochemical results of this study combined with the geophysical data show evidence of hydrocarbon potential of the study area.
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