Gas leakage from palaeogene reservoir in Assam - a geophysical puzzle

Abstract

Reports of gas leakage started coming since the beginning of 2012 from different localities in the Deohal area near the oil township Duliajan, Assam (India). The source was located in a gas reservoir in the Palaeogene sediments (Barail group). Multi-component seismic reflection methods which were highly successful to locate gas bearing zones at depths, were not very effective to locate the same in the shallow subsurface. From different types of electrical surveys conducted, self-potential (SP) method showed the most promising result. Probable SP was sensitive to high electrokinetic potential difference between the leaking and non-leaking zones.