Presence of tertiary and pre-tertiary source of hydrocarbon in Assam and Assam-Arakan basin: A case study in Suphayam area Pangtey Kusum Lata*, Chatterjee Sayani, Singh Sarita, Saraswat S. K., Neeraja P. Geochemistry Division, KDMIPE, ONGC, Dehradun *E-mail: Pangti_Kusumlata@ongc.co.in
Online published on 13 February, 2019. Abstract Geochemical investigation of oils and sediments of an area provides considerable information on the genesis of oils in the given area. Such a study helps in a better understanding of the petroleum system operative in an area. Molecular level geochemical characterization of oils, extracted from multiple formations and sediment samples in the Suphayam area of South Assam Shelf clearly brings out two genetic groups of oils by carrying out oil-oil correlation. One group comprising of low to medium gravity oils from Tipam, Bokabil and Barail Formations (Oligo-Miocene age) have been dominantly derived from terrestrial organic matter deposited in oxic to sub-oxic environment and are in an early phase of maturation (VRc: 0.66–0.69). These oils are characterized by Oleanane (>20%), Bisnorhopane (>40%), C28 regular Sterane (<27%) and moderate Bicadinane. The other group of medium to high gravity oils from Sylhet Formation (Eocene age) and the Basement have been derived from mixed organic matter deposited in an oxic to sub-oxic environment and are in a peak level of maturation (VRc: 0.75–0.80). These oils have Oleanane (<20%), Bisnorhopane (<19%), C28 Steranes (>33%) and very high Bicadinane. The oils from Miocene to Oligocene reservoirs in Suphayam area are genetically correlatable and sourced by Tertiary source rocks whereas the genetically correlatable oils from Eocene and Basement reservoirs are sourced by Pre-Tertiary source rocks. Source rock evaluation indicates the absence of effective source rocks in the study area. Custom kinetic based hydrocarbon generation/expulsion studies (1-D Modelling) at a low near Suphayam area and at a low in Dimapur reveals that kerogen transformation is below 10% in all the sedimentary sequences. Thus hydrocarbons in the study area seem to be sourced from Tertiary and Pre-Tertiary sequences from the adjacent Schuppen Belt. Top Keywords Hydrocarbon, Sylhet Formation, Geochemical Investigation, Genesis of oils. Top |