Integrated spectral decomposition and AVO analysis for determining reservoir distribution: A case study of jambi Sub-Basin, Indonesia

The reservoir distribution for a case study of Air Benakat Formation, Jambi Sub-basin has been delineated using spectral decomposition method and Amplitude Versus Offset (AVO). This study using spectral decomposition to identify the existence of gas reservoir in Air Benakat Formation (ABF), Jambi sub-basin and verified the result by using AVO analysis. Combination of this method could minimize the uncertainty of the subsurface model. The aim of this study is to delineate the gas reservoir by using both method and interpret the reservoir model based on both result. Spectral decomposition, in this research, was more specified in Continuous Wavelet Transform (CWT) due to its sensitivity characterizing clastic reservoir. By convoluting Morlet as background wavelet, we successfully performed CWT for our reservoir in three frequencies, which is 15 Hz, 25 Hz, and 40 Hz. Time-frequency map in 15 Hz shows high amplitude low frequency anomaly and presumed as the reservoir zone. Furthermore, the two others time-frequency maps not showing the amplitude anomaly. That showed the unique of CWT anomaly technique reading in characterizing hydrocarbon reservoir. For better conclusion, fine result of CWT was still verified with AVO analysis. AVO is one of the oldest methods that has well known to characterize hydrocarbon reservoir. Combination of AVO Analysis Parameters, Gradient and Intercept, has constructively supported CWT result with showing good anomaly only on the marked reservoir. Gradient reflects the reflection coefficient which is mainly different between hydrocarbon content and dry one, so does intercept which is sensitive with coefficient reflection changing by angle, where reservoir of this study showed Class 3 of AVO Analysis. This study concluded that combination of CWT and AVO analysis has capacity to delineate the hydrocarbon reservoirs, especially clastic reservoir.