THE STATUS OF GEOPHYSICAL KNOWLEDGE IN THE EAST COAST AND EASTERN BASINS OF INDIA

Abstract

The major problem in geophysical exploration for hydrocarbons in the east coast basins of India (Mahandi, Krishna-Godavari, Palar and Cauvery Basins) is to obtain persistent and correlatable reflection seismic data from prospective zones at depth. From the geological and well data a considerable thickness of pre-Tertiary and Tertiary sediments is known to be present in these basins. As these areas are covered with a blanket of alluvium, the basin configuration and sub-surface structural features are to be inferred from geophysical data. Although gravity, magnetic and refraction surveys have broadly outlined the basin configuration, suitable seismic reflection techniques are yet to be evolved for detailed mapping of the structures. Experiments using offset spreads and geophone grouping parameters derived from noise studies have yielded encouraging results in a limited area of the Cauvery basin.

The problems of the eastern basins (Assam, Tripura and Bengal) are varied in nature. The structures in the shelf area of Assam, have been successfully mapped using reflection seismograph, but the tectonic complexity of sub-thrust regions of the Naga Hills and the steeply folded belts of Tripura present formidable logistics and technical problems for delineating the sub-surface features. Some theoretical studies have been made for developing field techniques to improve the signal-to-noise ratio in these areas.

The problem in the Bengal basin is the absence of continuous and correlatable reflection events from the prospective Mio-Pliocene section. The use of digital data acquisition and processing techniques has not substantially improved data quality from this section to date.