Seismic avo analysis for shallow gas and gas hydrates accumulation

Amplitude versus Offset-AVO analysis is widely used in determination and classification of hydrocarbon reserves. AVO analysis is applied to bright spot and dim spot anomalies which are the indications of gas accumulations in the seismic sections. It is also used for determination of possible free gas accumulations below BSR reflections which indicate gas hydrate accumulations. 1B modeling studies have been performed to understand the behaviour of reflection amplitudes with increasing offset in a CDP gather and to compare them with the results from AVO analysis of real seismic data sets. AVO classes are shown on synthetic CDPs as well as on reflection coefficent ? incidence angle graphs. Different synthetic CDP groups are generated to compare the differences between the AVO responses of brine sand and gas sand interfaces.In this study, AVO analysis are applied to real seismic data which were collected aboard of R/V K. Piri Reis research vessel of Institute of Marine Sciences and Technology, Dokuz Eylul University. A shallow gas accumulation (a bright spot) and a BSR reflection were observed in seismic lines Mar10 from Marmara Sea and Kar11 from Black Sea, respectively. Partial stack sections and AVO attribute sections are computed for bright spot anomaly and BSR reflection. On the selected CDPs of both sections, AVO gradient analysis has been performed and crossplot graphs have been obtained. Both on the bright spot reflection in Mar10 seismic line and on BSR reflection in Kar11 seismic line, Class 3 and Class 4 AVO anomalies have been identified.