Geochemistry Division, KDMIPE, ONGC, 9 Kaulagarh Road Dehradun, India. Email: ashokraina59@rediifmail.com 10 th Biennial International Conference & Exposition P 246 Oil-oil and oil-source correlation by application of Compound Specific Isotopic Analysis (CSIA): A frontier tool applied to Kali-Kuthalam area in Cauvery Basin. Ashok Raina*, R.K.Saxena, H.C.Pande, Vartika Roy, A.K.Mittal & Anil Pande Summary The compound specific stable carbon isotopic characterization (CSIA) is a state-of-the-art geochemical technique to refine oil-oil and oil-source correlations. Using CSIA, the isotopic values of individual n-alkanes have been measured in the range of C17 to C30 for oil/condensates and also in bitumen of probable source sequences in Andimadam Formation in Kali-Kuthalam area, Cauvery Basin. Further the isotopic profiles of these n-alkanes in combination with the biomarker parameters have been applied to study organic matter input, depositional environment, and maturity of the source organics. CSIA profiles of most of the studied oils/condensates shows similar trend with small differences in their n-alkane carbon isotopic values. Most of the studied source sequences show poor correlation with studied oils/condensates due to the differences in their thermal maturities and organic facies variations. Some source sequences are correlatable but many oils exhibit higher maturity compared with these source sequences. Thus some deeper sediment can be major source. Keywords: Compound specific isotopic analysis (CSIA) Introduction Cauvery Basin, an intracratonic basin is situated along the southeastern part of Indian Peninsula. Commercial hydrocarbon accumulations have been confirmed in the Cretaceous and Tertiary sediments. Hydrocarbons have been discovered in almost all the sub-basins of Cauvery Basin. Kali-Kuthalam area, located along the north western rising flank of Tranquebar sub-basin, is one of the thrust area in Cauvery Basin put on fast track exploration. Commercial amounts of oil/gas/condensates have been discovered in multiple stacked sandstone reservoirs in Bhuvanagiri and Andimadam formations. Most of the hydrocarbon finds in this area are gas/condensates. So far fifteen pay sands are identified in Kuthalam area of which nine is gas bearing. The extensive source rock evaluation of all the sub-basins of Cauvery Basin has established that the Andimadam Formation of Lower Cretaceous sediments are the major source rocks in Cauvery Basin and organic matter is confined to two straitigraphic units, namely, Lower Cretaceous and Early Oligocene to Late Eocene (Banerjee et al., 2003 and Vyas et al., 2001). Of these, only the Lower Cretaceous sediments are matured enough to generate and expel hydrocarbons. The entire sedimentary sequences are recipient of good quantity of organic matter (upto 12% TOC). The hydrogen Indices are fair to very good in the depressional part (up to 300 mg HC/gm) of TOC. The organic matter is an admixture of Type-II & III, capable of generating both gaseous and liquid hydrocarbons (VRo 0.55-0.60, Tmax 435-440oC) (Vyas et al., 2001). The Geochemical data from deep wells indicated that the syn-rift Andimadam Formation is possibly the main source rock. This formation has been penetrated mainly in the flanks of depocentres where it was found to be dominantly sandstone with subordinate shales. It may become more shaly towards the sub-basin depocentres. The objective of the study is to evaluate oils covering all pay sands and probable source rocks in Kali-Kuthalam area through Compound Specific Isotopic analysis (CSIA) in combination with biomarkers to infer specific source organics and depositional environment.