Amplitude variation with offset responses for gas hydrate/free gas models: a case study

Gas hydrate is considered as a potential major energy resource for India. The presence of gas hydrate is inferred mainly by identifying an anomalous reflector, known as the bottom simulating reflector (BSR) on seismic sections. Understanding the properties of gas hydrate/free gas-bearing sediments and studying the amplitude-versus-offset (AVO) or amplitude versus incidence angle (AVA) characteristic from a BSR are important. The objective of the present work is to study the behaviour of reflection coefficient with angle of incidence for gas sand/shale and gas hydrate/free gas models. The amplitudes of reflected seismic waves are directly proportional to seismic reflection coefficients at an interface between different geological strata. The variation of AVO or AVA can be used in arriving at petrophysical/lithological models. The study shows variation in the reflection coefficient obtained by elastic impedance method and from Zoep-pritz equations. Different gas hydrate saturations show a positive, negative or no AVO anomalies in BSR.