Abstract

In older geological sequences like the Gondwanas, the interpretation of the radiation logs are adversely affected due to the presence of secondary minerals. The presence of such minerals in the Gondwana sequence of Krishna-Godavari Basin in East coast of India led to an unrealistic estimate of the porosity from logs.

The thin section studies of sandstones have shown the presence of felspar in significant quantity. This has decreased the bulk density of the formation and has given an optimistic estimate of porosity from the logs. Scanning Electron Microscope (SEM) studies have indicated the presence of illite as the main clay mineral. An insight to the cause of preservation of porosity in these Gondwana sandstones is brought out by the SEM studies.

Log-core integration has shown rapid vertical and lateral variations in facies. The study of petrophysical parameters has shown that the value of ‘m’ varies from 1.6 in the pay section to a value of more than 2.5 in the non-reservoir section. This has explained some anomalous Sw values encountered in the non-pay/poor reservoir section.