Integrated log analysis of Cretaceous sedimentary sequence of Ramnad sub–basin, Cauvery Basin, Southern India

In this paper, a detailed study has been undertaken by considering Seismic, Geology, Geophysical/Petrophysical and Geochemical data acquired in the drilled wells in order to have good understanding on the geological set up for building the suitable petroleum system and reservoir characterization for optimum reserve estimation and economic exploitation of proven hydrocarbons. Lithostratigrahic and biostratigrahic correlations have been examined. Paleobathymetry, depositional environment, reservoir rock composition, source rock studies and pore pressure studies have been carried out in general considering the well data of few representative wells drilled in the Ramnad sub basin. The inferred lithology in Nannilam formation is feldspathic sands associated with montmorillonite, mica and mixed clay, where as in Bhuvanagiri, lithology is mainly calcareous sandstone associated with silt and clay minerals namely chlorite, kaolinite and mixed clay. Depositional environment in Bhuvanagiri and Nannilam formations is found to be marine and coastal respectively, and this may be due to variations in paleobathymetry levels at the time of sediment deposition. Source rock studies inferred that Andimadam shale is the source rock for Nannilam and Bhuvanagiri reservoirs. This is rich in organic content with early maturation. The pore pressure and temperature studies indicate that there is no high pressure and temperature zone in this area and hence drilling and logging can be carried out under normal temperature and pressure regimes. This study forms ground work for carrying out the detailed field study in each fields of the Ramnad sub basin that will enable for augmenting the estimated/proven hydrocarbon reserves, locating the bypass/left over/missed hydrocarbons and also providing suitable solutions for economic exploitation.