Spectral decomposition' application for stratigraphic-based quantitative controls on Lower-Cretaceous deltaic systems, Pakistan: Significances for hydrocarbon exploration

Shoreface deltaic depositional systems (UDS) form excellent stratigraphic traps. The UDS are developed during the adverse sea-level conditions, which have a vital impact on the quantitative prediction of stratigraphic reservoirs. The prediction of accurate thickness and distribution of porous reservoir along the UDS is always a challenging job for exploration geophysicist. Since these oil and gas plays are purely thin-bedded reservoirs. They require a specific tuning frequency to resolve and predict the accurate thickness of the hydrocarbon-bearing zone. The band-limited seismic attributes are not reliable tools for developing cost-effective stratigraphic plays. The Fourier transformation tool such as continuous wavelet transforms (CWT) and thickness modelling for UDS (TMUDS) are executed on the gas-bearing UDS, Pakistan. Beyond the conventional amplitudes, the 37-Hz tuning block demarcates the gas-bearing reservoirs. The amplitude attenuation at 48-Hz validates the presence of coarse-grained sediments within the upper shoreface intervals of deltaic system. The blending of seismic, 37-Hz, and sweetness magnitudes completely recognizes the dominant reservoir fluids, which were unable to detect using the traditional mapping. The sweetness profile predicts a 20 m thick reservoir facie. The band-limited TMUDS reveals some tuning effects of ambiguous lithology and fluids. However, the post-stack seismic data processing within the designed amplitude spectrum of 12–55 Hz have greatly enhanced the physical parameters of thickness and presence of hydrocarbons. The 36-Hz trace sub-bands have predicted a 48 m thick reservoir facie along the UDS. The 36-Hz ESB confirms the presence of hydrocarbon-bearing coarse-grained deltaic facies, which are accumulated along the intersection point of shelf-slope of UDS. The quantitative plots of predicted thickness and acoustic impedances [AI] [g/c.c.*m/s] at 36-Hz CWT shows a strong correlation coefficient of R2 > 0.90. These observations take a lead over the band-limited amplitude-based seismic attributes for quantification for UDS. Hence, only the post-stack seismic data processing and interpretation based on the CWT wavelet can enhance the vertical thickness of the reservoir and the lateral extent with the least error. This workflow has robust stratigraphic implications for explorations for stratigraphic fairway for Lower Goru and acts as an analogue for local to regional clastic depositional systems within Asia and world similar depositional settings.