Petrophysical evaluation of well log data and rock physics modeling for characterization of Eocene reservoir in Chandmari oil field of Assam-Arakan basin, India

Petrophysical evaluation of well log data has always been crucial for identification and assessment of hydrocarbon bearing zones. In present paper, petrophysical evaluation of well log data from cluster of six wells in the study area is carried out in combination with rock physics modeling for qualitative and quantitative characterization of Eocene reservoir in Chandmari oil field of Assam-Arakan basin, India. Petrophysical evaluation has provided the estimation of fluid and mineral types, rock/pore fabric type and fluid and mineral volumes for invaded and virgin zones. Calibrations are made where core data were available. Rock physics study is carried out for analyzing the influence of porosity, mineral compositions and saturation variations on the elastic properties of the subsurface. The rock physics modeling allowed quantitative prediction of relationship between porosity, saturation (gas, oil and water), clay volume and the elastic properties. Cross-plots of different elastic parameters are generated to identify the lithology variability and pore-fluid type, and to establish likely distinction between the hydrocarbon bearing sands, brine sands and shale. The Eocene reservoirs are found to be primarily sandstone intermixed with incidental clay matrix and some calcareous cementation. Sands are interpreted to be continuous in most of the blocks. The effective porosity for these sands varies from 15 to 22% in most of the wells. A wide range of variation is observed in water saturation with lowest being 5%. Finally, a numerical rock physics model is prepared to predict the elastic properties of the rock from petrophysical properties.