--> Abstract: Petroleum and Source Rock Geochemistry of Tripura-Cachar Region of Assam-Arakan Basin, India; #90063 (2007)

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Petroleum and Source Rock Geochemistry of Tripura-Cachar Region of Assam-Arakan Basin, India

 

Mittal, A. K.1, M. Jha1, R. S. Bisht2, D.S. Rawat1, H.C. Pande1, I.V.S.V. Prasad1, S. Varshney3, A. Raina1, R.R. Singh1 (1) Oil & Natural Gas Corporation Ltd, Dehradun, India (2) Oil & Natural Gas Corporation Ltd, Mumbai, India (3) Oil & Natural Gas Corporation Ltd, Dehradun,

 

Tripura-Cachar region of Assam-Arakan Basin, situated in the north eastern part of India, is mainly a gas province with reservoirs in Miocene Bhuban and Bokabil sequences. Gases are often associated with minor quantities of condensates. Oil is produced from the Badarpur field of Cachar from upthrusted Renji sands of Late Oligocene. To unravel the origin of hydrocarbons in the region an integrated geochemical study has been carried out.

 

An assessment on the basis of geochemical data brings out that there is hardly any indication of effective oil and gas source in the penetrated Miocene sections of Tripura-Cachar area. Further, the study reveals that the gases accumulated in the Miocene reservoirs in Tripura-Cachar are of thermogenic origin, lean in C2+ hydrocarbons, genetically related and correspond to a maturity of ~1.0 to 1.2% VRo. Such maturities are expected within Oligocene Jenam shales in synclinal areas. The gases of Tripura-Cachar thus have probably migrated vertically along faults from deeper sources.

 

Oils of Badarpur and condensates of the region indicate a strong terrigenous source input with the deposition of source under fluvio-deltaic conditions. However, the oils are distinguished from the condensates by a very strong presence of bicadinanes in the oils. In contrast to the gas maturity, C29 sterane biomarker ratios show low to moderate maturity (0.65 to 0.75% VRo) for oils (Badarpur) and condensates of Tripura-Cachar area.

 

The observed oil and gas properties thus indicate that oil was generated and expelled by oil-prone Oligocene shales earlier (to gas) and the gas is the higher maturity product of the source. Three petroleum systems: Jenam-Renji (!), Jenam-Bhuban/Bokabil (!) and Bhuban-Bhuban (!) may have contributed for the gas/oil/condensate accumulation in the region. Traps within Miocene sediments will continue to be the major exploration targets to augment gas reserves in the Tripura-Cachar area.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California