Direct Hydrocarbon Indicators (DHI)

Abstract

The presence of gas in highly porous young sands significantly lowers the bulk modulus and typically creates high amplitude anomalies (bright spots) in seismic stack sections that make them direct hydrocarbon indicators (DHI). Though high amplitudes are more commonly a characteristic of gas, light and normal grade oil can also manifest high seismic amplitude responses. However, all bright anomalies may not be due to hydrocarbons and may need proper validation before drilling. Other related characteristics of gas reservoirs such as velocity and polarity, and associated phenomena such as ‘flat spots’, ‘shadow zones’ and time ‘sags’, manifested in seismic, can also act as indicators and may be considered for validating DHI amplitude anomalies for hydrocarbons. The genesis of high amplitudes is analyzed and DHI limitations outlined.