Abstract

The long-term seepage of hydrocarbons, either as macro or micro seepage, can set up near-surface oxidation reduction zones that favor the development of a diverse array of chemical and mineralogic changes. The bacterial oxidation of light hydrocarbons can directly or indirectly bring about significant changes in the pH and Eh of the surrounding environment, thereby also changing the stability fields of the different mineral species present in that environment. The paper reports the role of hydrocarbon micro seepage in surface alterations of trace metal concentrations. In this study trace metal alterations were mapped that appear to be associated with hydrocarbon micro seepages in the oil/gas fields. The soil samples were collected near oil and gas fields of Tatipaka, Pasarlapudi areas of Krishna Godavari Basin, Andhra Pradesh from a depth of 2 - 2.5m. The paper reports the chemical alterations associated with trace metals in soils that are related to hydrocarbon micro seepages above some of the major oil and gas fields of petroliferous region of Tatipaka and Pasarlapudi areas of Krishna Godavari Basin, India. The soil samples for trace metals; Scandium (Sc), Vanadium (V), Chromium (Cr), Cobalt (Co), Nickel (Ni), Copper (Cu), Zinc (Zn), Barium (Ba) and Strontium (Sr) were analyzed using Inductively Coupled PlasmaMass Spectrometry (ICP-MS). The concentrations of Sc (8.01 to 39.737 ppm), V (197.31 to 489.51 ppm), Cr (106.5 to 287.54 ppm), Co (30.92 to 51.94 ppm), Ni (65.04 to 109.95 ppm), Cu (87.73 to 131.35 ppm), Zn (88.51 to 470.84 ppm), Ba (263.52 to 3091.55 ppm) and Sr (119.45 to 217.62 ppm) were obtained. Integrated studies of trace elements over adsorbed light gaseous hydrocarbons (?C2+) anomalies showed good correlation with the existing oil and gas wells. The increase in trace metal concentrations near oil/gas producing areas, suggests a soil chemical change to a reducing environment, presumably due to the influence of hydrocarbon micro seepage, which could be applied with other geo-scientific data to identify areas of future hydrocarbon exploration in the frontier areas.