Detection of Gas Reservoir at Banyuasin Field by using Amplitude versus Offset (AVO) Analysis

Abstract

Banyuasin Field is indicated to have gaseous hydrocarbons based on well data. The purpose of this study is to examine the distribution of gas hydrocarbons in the Telisa and Talang Akar Formation, which are reservoir rocks that are dominated by sandstone lithology. Amplitude versus Offset (AVO) analysis is used as a method in this study, based on the response to changes in amplitude at the offset/angle. To determine AVO responses towards seismic data, gradient analysis and AVO product were performed using the intercept and gradient attributes. Gradient analysis is made by making intercept-gradient graphs in determining the type of fluid based on the AVO class. The AVO product is a result of multiplication between the intercept and gradient so that the distribution of gas hydrocarbons on a seismic cross-section can be seen. Based on the results of the analysis on the Telisa Top Formation in Zone 1, AVO response of class III was obtained, which indicated the presence of gas hydrocarbon and Zone 2 AVO response of class II P and I was obtained which indicated the presence of wet sand. The top of the Talang Akar Formation in both target zones is identified as an AVO class IV response, indicating the presence of coal. The difference in response is caused by the impedance contrast of the sandstone in the target zone. For gas hydrocarbons, the impedance response of sandstone is small because the layer of porous sandstone is filled with gas. This causes magnitude of Vp to become smaller than Vs which causes the amplitude to increase as the offset/angle increases and AVO product has positive value on the seismic section.