Light gaseous hydrocarbon studies in the near-surface soils of Tatipaka, Pasarlapudi and Kaza areas of Krishna–Godavari Basin, India

One hundred and thirty-five soil samples were collected from a depth of 2–2.5 m near oil and gas fields of Tatipaka, Pasarlapudi, Ponnamanda, Kaza and Palakollu areas of Krishna–Godavari Basin, Andhra Pradesh, India and were analysed for light hydrocarbon gases. The adsorbed soil gas analysis showed the presence of moderate to low concentrations of methane (CH4; 2–83 ppb), ethane (C2H6; 1–92 ppb), propane (C3H8; 1–134 ppb), butane (n-C4H10; 1–187 ppb), pentane (n-C5H12; 1–316 ppb) and ∑C2+ sum of C2H6, C3H8 and n-C4H10 (1–729 ppb) in the soil samples of the study area. The carbon isotopic composition δ C1 of the samples ranged between – 36.6‰ and –22.7‰, which indicates thermogenic origin of methane. Observed concentrations of adsorbed light hydrocarbon gases in soils have shown an interesting correlation of surface light hydrocarbon anomalies with the subsurface oil and gas accumulation in the study area, demonstrating the usefulness of adsorbed soil gas technique in petroleum exploration.