Petroleum and
Source Rock Geochemistry of Tripura-Cachar Region of
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
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