Current Science

M. A. Rasheed ¹, M. Lakshmi ², M. S. Kalpana ², D. J. Patil ², A. M. Dayal ²

Affiliations
1 Gujarat Energy Research and Management Institute (GERMI), Gandhinagar 382 421, IN
2 CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad 500 606, IN

Abstract

The present study aims at exploring the possible correlation between adsorbed light gaseous hydrocarbon distribution pattern and the hydrocarbon oxidizing microbes present in the sub-soil samples. To establish the role of the latter in identifying the upward migration of hydrocarbons, especially a known petroliferous Krishna-Godavari Basin has been investigated. Soil samples from oil and gas fields of Tatipaka and Pasarlapudi areas of the basin show the presence of bacterial population for methane (3.46 × 10⁵ cfu/g), ethane (3.85 × 10⁵ cfu/g) and propane (3.04 × 10⁵ cfu/g) oxidizing bacteria in soil samples. Gas chromatographic analyses of adsorbed soil gases show the presence of C₁ to C₄ hydrocarbons. The concentration of adsorbed soil gases ranged for methane (C₁) = 1 to 115 ppb, ethane (C₂) = 1 to 99 ppb, propane (C₃) = 1 to 34 ppb, butane (nC₄) = 1 to 9 ppb and ΣC₂₊ = 1 to 115 ppb. The scatter plots between C₁ and C₄ components depict a linear trend indicating that all gases are from the same source. The total organic carbon (TOC) content of the soil samples ranges from 0.18% to 1.34%. Pearson correlation analysis shows that the concentration of ΣC₂₊ does not show any correlation (r = 0.1) with TOC, suggesting that the adsorbed gases are not derivatives of the organic carbon. Moreover, the values for methane δ¹³C₁ varied from -39.9‰ to -19.9‰ (V-PDP) Vienna PeeDee Belemnite indicate thermogenic origin. The integration of geomicrobial prospecting method together with adsorbed soil gas and carbon isotope studies shows a good correlation with the producing oil and gas fields of Krishna-Godavari Basin.

Keywords

Adsorbed Soil Gas, Bacteria, Hydrocarbon Exploration, Microseepage.

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