عنوان مقاله [English]
Amplitude Variation with Offset (AVO) is one of the effective methods for identifying the fluid type in subsurface exploration. In this paper, we investigate the existing of light hydrocarbon in Gorgan Plain with Direct modeling and Inverse modeling as an AVO analysis. Direct Modeling can indicate the identity of attributes (litho logy or fluid dependent attributes). The analysis has been done using both P-P and P-Sv attributes. Inverse modeling deals with real data and is fed from the results of direct modeling for detection of the light hydrocarbon zones. Using this methodology in Gorgan Plain showed that attributes which are related to converted attributes such as S-wave Impedance Reflectivity and S-wave Velocity Reflectivity have higher ability in identifying fluid from litho logy with respect to non-converted attributes for example P-wave Impedance Reflectivity and P-wave Velocity Reflectivity. Making the inverse sections of fluid-dependent attributes indicated two light hydrocarbon zones under the Cretaceous-Tertiary unconformity. It expects that there have been wet zones under them. By investigation on three inverse sections of density contrast, P-Wave velocity contrast and S-Wave velocity contrast with considering Ramos & Castagna graph , It is concluded that the amount of Sw is about 90% and the amount of Sg will be approximately 10%.