Abstract

Amplitude anomalies have been the significant tool for exploration of hydrocarbon as bright spot/DHI for manyyears for the Geoscientists. This has proved to be important in some places and in some formations whereas it has failedat some places. Since it is one of the quick look interpretation skills, it is still adopted by Geoscientists for obtainingconfidence. However validation of the anomalies is done through different petro physical analysis. Tapti Daman sector inthe Western offshore basin has been explored widely based on the amplitude anomaly analysis. Success and failures bothhave been observed from this sector of the basin. Late Oligocene Daman formation has been explored in this basin from2D seismic data to 3D seismic data. The amplitude anomalies which failed for the upper part of Daman formation has proved successful for lower part. The Western part of Tapti Daman sector covering part of Diu Arch has been exploredwidely based on the amplitude driven exploration. High amplitude anomalies depicting presence of thick channel sandproved to be water bearing after drilling. The shales within the Daman formation are low impedance shales and water bearing sands are high impedance sandstones. In this paper an attempt has been made to analyze the lithology and their respective impedance in the western part of Tapti daman sector on the eastern flank of the Diu arch. The lower part of Daman formation having thick net gas bearing sand of 15-18m has been explored which has no impact on amplitudeanomaly whereas in upper part of Daman formation high amplitude anomaly corresponding to the channel sand has been found water bearing. Cross plots of the logs have been attempted and the shales of the area are analyzed in finer detail. It has been found that the shales are dominantly silty in nature, thus reducing fissility. Sandstones are also silty innature and found to be unconsolidated at some places, hence posing problem of sand incursion in well testing and well completion. The analysis of the impedance of the lithology and pay sands from logs is then compared with seismic data. The analysis suggests that the shales in the lower part of Daman formation are predominantly high impedance shales having impedance values close to that of Gas bearing sands. Thus it becomes difficult to differentiate between the Gas bearing sands and shales. The shales in the upper part of Daman formation are clean and devoid of silt, hence havinglower impedance values.