Appraisal of tectonically-influenced lowstand prograding clinoform sedimentary fairways of Early-Cretaceous Sember deltaic sequences, Pakistan using dynamical reservoir simulations: Implications for natural gas exploration

Abstract

The Early Cretaceous reservoir system of the Indus basin has a suite of stratigraphic-based trapped petroleum plays such as the fluvial-dominated channelized systems, shallow marine incised valley systems, and lowstand prograding clinoforms. However, the seismically-imaged Lowstand prograding clinoform plays (LCP) are hot topics in the stratigraphic-based hydrocarbon traps-bearing traps fairways. These LCPs remain established throughout an extensively falling sea level with succeeding growth, which fills these LCPs with gas-saturated reservoirs. The LCP remains mud-dominated, which has created ambiguous expressions in full-spectrum seismic. Hence, they in turn complicate the prediction of the stacking patterns of the depositional parasequences, the source of sedimentary influx, the angle of stratigraphic traps, and their controls on the vertical/lateral migration of hydrocarbon-bearing fluids. The bandlimited seismic amplitude lacks the tuning frequency, which is one of the key parameters in the seismic sedimentological analysis given the above-mentioned constraints. This study connects the broadband spectral analysis with the bandlimited seismic amplitude-based attributes to quantify the LCP using wavelet transform-based impedance-decomposed porosity-gas-saturation of velocity and density simulations (PGVDS). The seismic amplitude and 23-Hz CWT attribute have allowed the detection of vertical thickness, lateral distribution, and angle of coarse-grained and fractured sigmoidal LCP facies of 22 m, 6 km, 7°, and 26 m, 12 km, 5°. The PGVDS have predicted the thickness, density, and velocity for porous gas-saturated LCP as 31–34 m, 2.1–2.15 g/c. c, 80–85%, 29–32%, 2139–2304 m/s, and non-porous water-saturated LCP as 18–28 m, 2.2–2.39 g/c. c., 60–75%, 17–25%, 2863–3108 m/s. The PGVDS have also imaged the highly fractured and laterally continuous fluvial-dominated onlapping channel-filled reserves that served as a source of generating a high impact of sedimentary influx within aggradational stacking patterns for gas-saturated (80–85%) sedimentary facies of LCP at an angle of zero degrees and porosity range of >30%. The lateral changes in the densely fractured network validate the facies-controlled migration of hydrocarbon-bearing reserves within the LCP, which implicates the development of regionally developed stratigraphic-based trapping plays throughout the basins of Pakistan. This study has categorically broadened the impact of connecting the spectral attributes of inverted reservoir simulations in inferring the geometry, extent, thickness, and distribution of hydrocarbons in prograding clinothems inside the Indus Basin. Hence, this research can serve as an analogue for the exploration of worldwide LCP with similar geological conditions.