Abstract

An attempt has been made to identify Clay Mineralogy, to determine depositional environment and to frame a petro physical model using open hole well logs,namely NGS (Natural Gamma Ray Spectroscopy), ECS (Elemental Capture Spectroscopy), Litho Density and Neutron logs, recorded in Vashista, an offshore upcoming exploratory field in Krishna - Godavari Basin.Three exploratory wellsX1, X2(gas bearing) and X3(dry well) are drilled in this field.In the present study, a detailed analysis has been carried on open hole well log data.Reservoir sands are mostly channel sands as evident from log motifs. A number of cross plots with various combinations (Ex.KvsPef, Si (vs) Al etc.,) are generated forthese wells.These cross plots shown at Serial No. 1 to 9 are nearly identical for two gas bearing wells, whereas a little deviation in the distribution of data points for the 3rd well, which went dry probably due to absence of lateral seal. Smectite-Mixed layer clay mineralogy isevident from the cross plots. NGS ratio cross plot (Sl.No. 9) infers that the depositional environment is of neutral to non marine with most of the data havingTh/U ratio in the range of 4 to 30.This cross plotalso indicates that the clay mineralogy in the formation under study is of Smectite-Mixed layer type. These results are inagreement with that of laboratory studies carried out in nearby G1 Field.