Bacteria as indicators for finding oil and gas reservoirs: A case study of the Bikaner-Nagaur Basin,

Geo-microbial prospecting for hydrocarbons is an exploration method based on the seepage of light gaseous hydrocarbons from oil/gas reservoirs to the surface and their utilization by hydrocarbon oxidizing bacteria.These bacteria utilize hydrocarbon gases as their sole source of food and are found to be enriched in the near surface soils/sediments above the oil and gas reservoirs.The detection of anomalous populations of n-pentane and n-hexane oxidizing bacteria in the surface soils can help to evaluate the prospects for hydrocarbon exploration.A geo-microbial survey has been carried out in the Bikaner Nagaur basin to investigate the prospects for hydrocarbon exploration.In the present study,bacterial counts for n-pentane utilizing bacteria range between 2.0× 102 and 1.26× 106 cfu/gm and n-hexane utilizing bacteria range between 2.0× 102 and 1.21 × 106 cfu/gm.The bacterial concentration distribution maps show four distinct anomalies in the study area.The possibility of discovering oil or gas reservoirs using the microbiological method is emphasized by the fact that the hydrocarbon-oxidizing bacteria range between 103 and 106 cfu/gm in soil/sediment receiving hydrocarbon micro-seepages.In the present study area of the Bikaner Nagaur basin,n-pentane and n-hexane utilizing bacteria are found between 105 and 106 cfu/gm of soil sample,which is significant and thereby substantiates the seepage of lighter hydrocarbon accumulations from oil and gas reservoirs.Geo-microbial prospecting studies suggest that hydrocarbon micro-seepage of subsurface origin is present in the study area and indicate that the area has positive prospects for petroleum exploration.