Delineating the shallow‐marine stratigraphic traps of Lower‐Cretaceous incised valley sedimentation, Pakistan using post‐stack seismic colour inversion

Abstract

Sub-surface incised marine valleys form good reservoirs globally. Subsurface heterogeneities within thin-bedded shallow-marine sedimentary systems are complex developing petroleum plays during hydrocarbon exploration. A seismic colour inversion (SCI) tool is a useful component in seismic data analysis for predicting porous and hydrocarbon-bearing reservoirs. In the present study, SCI was used for the demarcation of gas-bearing stratigraphic sequences within the Indus Basin, SE Pakistan. The SCI better characterizes the gas-bearing sand-fills within the incisedvalley reservoir compared to the absolute average amplitude (AAA) derived from surface seismic data. The SCI tool enhances the structural configuration of numerous system tracts; including the lowstand system tract (LST) and transgressive systems tract (TST): phase shifts reveal 'sweet-spots' within the faulted and sand-filled incised valley. The gas-bearing sand-filled incised valley of the LST experiences phase reversals with SCI magnitudes of −5900 g/c.c.*m/s, which reflect the bright seismic responses for stratigraphic-based reservoir characterization, and hence it may act as a direct hydrocarbon indicator (DHI). The TST, which proves to be the non-reservoir segments of seal sediments, brightens the high-acoustic impedance (A.I) SCI magnitudes of 5900 g/c.c.*m/s. Facies modelling discriminates the transgressive seal and regressive coarse-grained sandstone-filled incised valleys. A cross-plot of SCI with net-to-gross (N/G) and porosity evidence remains an accurate thickness and porosity effects for sand-filled incised valley reservoirs than compared to AAA.

Delineating the fluvial sedimentary reservoirs of Cretaceous sedimentation using seismic attributes and seismic‐petrophysical simulations, Southwest Pakistan

“…The exploration region is composed of a short time window of Lower‐Cretaceous channel system gas‐bearing facies within the ~1.9–2.5 s (Figure 3a). Amplitude‐derived features and posture have been effective in eliminating and indicating the stratigraphic pool (Naseer, 2021). Seismic amplitude and CWT attributes were applied for stratigraphic reservoir analysis (Figures 6 and 7) (Naseer, 2021).…”

“…Amplitude‐derived features and posture have been effective in eliminating and indicating the stratigraphic pool (Naseer, 2021). Seismic amplitude and CWT attributes were applied for stratigraphic reservoir analysis (Figures 6 and 7) (Naseer, 2021). Therefore, the amplitude‐based seismic profiles were used to quantify the stratigraphy and the amplitude responses for the sandstone and shales of the Lower Goru Member and the basal sand within the fluvial depositional system.…”

“…This tool estimates the diverse problems of the thickness of the reservoirs and the frequency, which are very sensitive to image the thick channel. SD analysis can be focused exclusively on forecasting the most precise locations for drilling the porous ones within the clatic and carbonates depositional systems (Naseer, 2021). Hence, the CWT was used to pick the stratigraphically identified events (Figures 5-7).…”

Seismic attributes and spectral decomposition-based inverted porosity-constrained simulations for appraisal of shallow-marine lower-Cretaceous sequences of Miano gas field, Southern Pakistan

“…The extensional basins of Pakistan have been extensively explored for stratigraphic plays. There is a suite of stratigraphic fairways, including the sandstone-filled fluvial channel system, incised valley, and shoreface depositional systems [ 34 , 45 , 47 , 49 , 50 ]. Previous researchers have applied seismic attributes to delineate fluvial depositional elements, such as channelized sandstone-filled point bars [ 47 ].…”

“…As a result, amplitude-based and frequency-dependent CWT properties are required for application to the seismic volume, in particular when the sea level is falling and the erosional zones are highly intermixed within the reservoir segments. Therefore, the identification of coarse-grained and ultra-thin-bedded stratigraphic-founded reserves is not predictable by executing this traditional map [ 50 ]. These stratigraphic limitations delayed the prediction of incised valleys and upper shoreface depositional systems.…”