Thin bed reservoir delineation using spectral decomposition and instantaneous seismic attributes, Pohokura Field, Taranaki Basin, New Zealand

Abstract

Nowadays, the amount of petroleum in the thick bed starts decreasing; thus, the thin bed hydrocarbon reservoirs are the alternative targets of hydrocarbon production. Thin bed reservoirs can maintain the reserves of the hydrocarbon. However, conventional seismic interpretation cannot delineate the thin bed reservoir that its thickness is smaller than the vertical resolution. Therefore, spectral decomposition and instantaneous seismic attributes were used to delineate the thin bed in this study. Short Window Discrete Fourier Transform (SWDFT) spectral decomposition and instantaneous frequency attributes were used to reveal the thin bed reservoir, while hydrocarbon bearing zone used Continuous Wavelet Transform (CWT) spectral decomposition and envelope (instantaneous amplitude) attributes to indicate the zone. Mangahewa Formation is the most productive hydrocarbon in Pohokura Field, Taranaki Basin, New Zealand. The uppermost part of Mangahewa Formation in the study area at Pohokura Field was selected for analysis. The study results indicate that 72 Hz SWDFT isofrequency section and map can reveal the thin bed that is confirmed by the instantaneous frequency attribute. The hydrocarbon accumulation area of the thin bed target is indicated by showing the high anomaly of envelope attribute. Moreover, the CWT spectral decomposition shows the low-frequency shadow zone and abnormal seismic attenuation in the higher isofrequencies contents below the thin bed which confirm the prospected hydrocarbon zone of the thin bed.