Syed Akbar
Hyderabad: Kadapa, notorious for bombs and bloodshed, will soon become the newest destination for exploration of oil and natural gas in the country with the National Geophysical Research Institute discovering hydrocarbons in the Kadapa (Cuddapah) basin.
Joint studies by the city-based NGRI and the Directorate-General of Hydrocarbons, Noida, have established the hydrocarbon resource potential of the Kadapa basin. Kadapa basin is an ancient geological structure with rich resources of oil and natural gas, and it could well become the next destination for hydrocarbon exploration in the State after Krishna-Godavari basin.
Presence of natural gas and oil is detected by several methods. The NGRI employed "adsorbed soil gas" methods as well as the presence of bacteria to find out hidden hydrocarbon resources. Light hydrocarbons like methane, propane, ethane and butane come out of the soil either in large or minute proportions.
If the leakage is in large quantities it can be identified easily. But in most of the cases the gases coming out are in small quantities which cannot be identified. However, in such cases certain bacterial groups live there eating these gases. The presence of these bacteria in large groups signifies that hydrocarbons are hidden underneath the earth. The NGRI studied the soil samples and took up adsorbed soil gas and microbial studies in Kadapa basin to establish the presence of oil and natural gas.
"The adsorbed soil gas studies and the inferences from geological, geophysical and other geochemical data, suggest that the demarcated areas around Nandyal and Koilakuntla may be potential for future hydrocarbon research and exploration. The Kadapa basin has hydrocarbon resource potential and efforts are on to conduct close sampling in the anomalous hydrocarbon zones," said Dr AM Dayal, head of the department of Stable Isotope and Surface Geochemical Prospecting for Hydrocarbon, NGRI.
Kadapa is an epicratonic Proterozoic basin situated over a length of 440 km and a width ranging from 150 km to 200 km. The Kadapa basin covers an area of 44,500 sq km extending into the districts of Kadapa, Kurnool, Anantapur, Prakasam and even Raichur in Karnataka.
The NGRI-DGHC teams collected 304 soil samples with spacing of four to five km along certain roads in the basin. Analysis showed 87 per cent of soil samples fall in the oil zone and remaining in the gas-condensate zone, Dr Dayal said.
Sample points with higher concentration of methane (more than 35 ppb) are clustered north-northwest and southwest of Nandyal and south-southwest of Koilakuntla with a few scattered anomalies all over the study area. The hydrocarbon anomalies obtained in the soil samples near Nandyal correlate with the good sediment thickness in the range of 6000 to 9000 metres for the Nandyal shale, which is considered as an ideal cap rock and potential target for petroleum exploration.
Frequently occurring carbonaceous shales with strong microbiotic content at different stratigraphic levels like Vempalle, Tadipatri, Cumbum and Pullempet formations also indicate petroleum source rock potential of the basin, Dr Dayal said. The structures like synclines, anticlines, fault closures in the Kadapa basin play an important role in hydrocarbon generation and entrapment.
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