Applying Petroleum Geochemistry to Search for Oil - a Unique Oil Find in a New Pay Sand -Kali-Kuthalam Area, Cauvery Basin,India

Neeraja N. Putcha, Mangalam V. Hargopal, Swamy Radha Anjeneya, and Jitendrac Prasad
Chemistry Lab, ONGC, Chennai, India

In the well KA # 33, a new sand just above basement, produced a very different oil, dissimilar to all other oils of Kali-Kuthalam area. This Naphthenic, light oil (37.3API), with high wax content (16.7%) has high cycloalkane content also. Isoprenoids ratio (Pr / Ph) , crossplot of Pr / nC17 vs Ph / nC18 & molecular composition indicates generation of this oil from algal/marine Type II kerogen deposited in strongly reducing (lacustrine?) environment at a moderate maturity level of the source. The high asphaltenes, lube, and low gasoline contents suggest that oil has migrated short distance only. The gaseous hydrocarbon present in the same reservoir, is an oil associated gas generated in main catagenetic phase of maturation. Presence of Helium (300ppm) in this gas and in almost all gases of Kali-Kuthalam area (260 - 1300 ppm) suggests a regionally good caprock.

Analysis till date on 92 liquid and gaseous hydrocarbons distributed in 16 sands in Kali-Kuthalam area indicate that 80% of the oils are very light (API>50) and only 15 % of the oils have wax contents between 5-10%. All the oils are paraffinic to ultra-paraffinic. Isoprenoid ratios, biomarker and Isotopic values for all oils indicates dominantly Type III source organics deposited in peat-coal to swamp conditions. Maturity indicators suggest two groups of oils generated at two different maturity levels.

Insitu source rocks have a mixture of type III & II in varying proportions. Presence of type I algal matter in some layers of Lower Cretaceous is observed in KA-13, 22, 23 and 25.

KA # 33 is drilled in the northern most part of the main field of Kuthalam area and is separated by a depression with the Kali field. From geochemical point of view, exploration in the vast depression between Kuthalam main field and Kali area warrants attention for exploration.

Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery