ABSTRACT
Carbon isotope fractionation associated with the aerobic consumption of propane (C3) were determined using Rhodococcus rhodochrous MTCC 291 bacterial strain to estimate the amount of hydrocarbon oxidized using GC, fractionation of δ13C carbon isotopes of propane and CO2 using GC-C-IRMS and growth of bacteria by UV-Visible Spectrophotometer. The initial δ13C isotopic value of propane was -34 ‰ and after incubation the changes of the isotopic values have been determined on 6th, 10th, 14th, and 17th days. The propane isotopic fractionation value was found to be maximum of -38.0 ‰ with an average value of -36.5 ‰ and a standard deviation of -1.22 ‰. The initial δ13C isotopic value of CO2 was -19.601 ‰. The CO2 isotopic fractionation value was found to be maximum of -29.153 ‰ with an average value of -26.859 ‰ and a standard deviation of -28.338 ‰. The consumption of propane gas was estimated using Gas Chromatograph. The initial concentration of propane in control was found to be 53 ppm. On incubation, the consumption of the propane gas was observed to be of 26 ppm. The carbon isotope fractionation presented here may be applied to estimate the extent of C1-C4 oxidation in natural gas samples, and should prove useful in further studying the microbial oxidation of these compounds in the natural environment.
ABSTRACT
Several techniques are used for the exploration of hydrocarbons, of which; the geochemical techniques involving the microbiological technique use the principle of detecting the light hydrocarbon seepage activities for indication of sub-surface petroleum accumulations. A survey was carried out to characterize the light gaseous hydrocarbons seeping in oil and gas fields of Krishna-Godavari basin of Andhra Pradesh. A set of 50 sub-soil samples were collected at depths of about 3 m for geochemical analyses and 1m for microbiological analysis. The microbial prospecting studies showed the presence of high bacterial population for methane 2.5 x 102 to 6.0 x 106 cfu g-1, propane 1x102 to 8.0 x 106 cfu g-1 in soil samples. The adsorbed soil gas analysis showed the presence of moderate to low concentrations of methane (26 to 139 ppb), ethane (0 to 17 ppb), propane (0 to 8 ppb), butane (0 to 5 ppb) and pentane (0 to 2 ppb) in the soil samples of the study area. Carbon isotope analysis for methane (´13C1) ranging from -36.6 to -22.7‰ Pee Dee Belemnite (PDB) suggests these gases are of thermogenic origin. Geo-microbial prospecting method coupled with adsorbed soil gas and carbon isotope ratio analysis have thus shown good correlation with existing oil/ gas fields of Krishna-Godavari basin.