Evaluation of AVO analysis for detection of gas sand reservoirs in onshore East Malaysia.

Abstract

Amplitude variations with offset (AVO) analysis which is primarily applied to the prestack seismic gathers has been a topic of great interests as it is expected to provide us with more confident indication of hydrocarbon accumulation than simple investigation of the specific anomalies in the stacked seismic section does.AVO analysis was evaluated for potential indicator of gas sand reservoirs on the seismic data of an area onshore East Malaysia of which the stratigraphy is dominated by sand-shale sequence under deltaic environment of Tertiary age. There are two prospects of interests of which one has been confirmed that hydrocarbon be accumulated in a number of sandstone reservoirs and the other remains untested. AVO has been modeled at the tops of three gas reservoirs, which indicates significant increases in amplitude with offset (AVO anomalies) to be expected for all gas reservoirs.Seismic data was processed to be suitable for AVO analysis. Specific data conditioning and enhancement techniques to preserve amplitudes of the data were employed. These techniques include true amplitude FK filtering and time and space variant offset dependent residual amplitude correction.AVO was analyzed by investigating restricted angle stack sections and partially stacked angle traces of the processed data. Significant AVO anomalies were correlated with some of the tops of hydrocarbon reservoirs particularly gas reservoirs which exhibited considerably high amplitudes on stacked section. However, any significant AVO anomalies were not observed in the seismic data acquired on the untested structure.