Source rock characterization from wireline logs in Tapti-Daman area, Bombay Offshore Basin, India

摘要

The rich marine source rocks generally have high radioactivity, which is reflected on gamma ray logs. Source rocks with high organic matter content have a low bulk density because of the low density of organic matter. They are also characterized by high formation resistivity, high neutron porosity and high sonic transit time, on wire line logs. The Paleogene source rocks of Tapti-Daman area have the highest source rock potential in Bombay Offshore Basin. The source rocks in the sub-basin have huge thickness ranging from 1000m to more than 3000m in the basinal part, comprising predominantly in the lower part and siltstone, shale and sandstone in the upper part, representing the prodelta shales and silt and shallow marine shales. The average TOC of the Paleogene sequence ranges from 0.8 to 3.45 % for the upper part and 1.16 to 5.18 % for the lower part with many intervals 10% and upto 19%. The maturity data indicates that the vitrinite reflectance ranges from 0.49 to 1.61% indicating that source rocks are falling within the main phase of oil generation. An attempt has been made to identify the organic rich source rock intervals and integrate with measured geochemical data. The relationship between the total organic rich resource carbon content (TOC) and the log derived bulk density of the corresponding intervals of Paleogene sequence of wells in Tapti-Daman area has been established. In addition, the relationship between sonic transit time and the maturity indicator vitrinite reflectance (Ro) has also been attempted.