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Evaluation of Thermal Maturity in Source Rocks and Gas/Condensates of Ramnad and Southern Part of Palkbay Area

Sukumar Pahari, Harvir Singh, Ivsv Prasad, and R. R. Singh
Geochemistry, KDMIPE,ONGC, Dehradun, India

Hydrocarbon potential in Cretaceous and Tertiary sediments of Ramnad and southern part of Palkbay area of Cauvery Basin has been evaluated to identify the potential source rocks, assess the nature and maturity of source rocks and gas/condensates and possible leads for future exploration. Fair to good source rock development has been observed within the Albian sediments only. The sediments from Late Cretaceous to Oligocene of studied wells are immature although these sediments have poor to fair hydrocarbon generation potentials.

Burial and thermal maturity construction reveals that at PBS_west location of south Palk bay area none of the sedimentary sequences attained condensate and wet gas zone maturity (1.3%VRo), whereas at RMD_low location in Ramnad area, Pre-Albian sedimentary sequences below 5650m attained condensate and wet gas zone maturity. At Ramnad-low location, Cenomanian and Pre-Albian sediments attained maturity equivalent to 0.7% VRo at 82 mybp and entered into condensate and wet gas zone maturity at 20mybp. At PBS_west location, Pre-Albian sediments attained maturity equivalent to 0.7% VRo at 65 MYBP.

All the oils are normal condensates, paraffinic in nature and might have generated from mixed marine Type II/III organic matter deposited in sub oxic to peat swamp environment. All the condensates are mature and differ slightly in maturity depending on the different maturity level of the same source facies. The gas/condensates of Ramnad sub basin have originated from thermal processes and have thermal maturity equivalent to 1.1-1.6%VRo based on these diamondoid ratios. Best targets for future exploration are deep centered gas in study area.

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