Palynofacies, maturation and source rock potential in Krishna-Godavari Bassin, India

Abstract

Studies on palynofacies and thermal alteration index (TAI) were carried out in the subsurface sequence encountered in nine drilled locations of Krishna-Godavari Basin for source rock evaluation of the Late Cretaceous-Tertiary sediments. The dispersed organic matter, as a whole, is considered mostly land-derived. The composition of the organic matter is a dominantly mixed type. A higher degree of sapropelization is recorded in the Late Cretaceous-Palaeogene sequence as compared to Neogene. The organic maturation as suggested by TAI values indicates that the maturation level of ‘Oil Window’ (TAI = 2.5) reached in the Late Palaeocene (53.60 Ma) in A, B, F, and E locations. Younger levels of maturation are noted as Middle Eocene (43·49 Ma) in C and D and Early Miocene (13-16 Ma) in G, H and I location. It is further observed that the occurrence of the youngest level of ‘Oil Window’ maturation lies between 80°-100° C. which appears the effective cooking temperature for the kerogen in the basin. Based on palynofacies development and TAI values, the sediments within the mature zone are considered to possess good source rock quality to generate the mixed type of hydrocarbons in the maturation range of TAI 2.5 to 3.0.