Seismic attributes and quantitative reverse reservoir simulations of shallow-marine eocene sedimentary fairways, extensional rifting Indus onshore petroleum system, southern Pakistan: Implications for hydrocarbon exploration

Abstract

Quantitative reservoir characterization plays a vital role in exploring carbonate depositional systems. The subsurface vertical and lateral changes in the tectonics and sea level adversely impact the signatures of band-limited seismic data. The seismic amplitudes are very sensitive to these vertical and lateral tilts of the stratigraphy and sedimentology of the subsurface stratigraphic layers. The dynamical tectonic-based fluctuating sea creates vital seismic expressions of high amplitude. These seismic expressions can inversely infer the dense-fractured depositional parasequences, thickness, porosity, and lithological change for the accommodation space and the sedimentary influxes for the development of petroleum fairways. Hence, it becomes very challenging to predict whether the producing zone for hydrocarbons sourced from the wet-gas-bearing zones is a potential zone for hydrocarbon exploration or a light oil-bearing zone (WGZ or LOZ). Therefore, the development of reverse quantitative simulations of parasequences within the extensional regimes is always a very complex research problem during stratigraphic-based fuel exploration of thin-bedded carbonate systems. This research utilizes the spectral-based amplitudes along with the instantaneous waveform-based temperature-porosity stratigraphic simulations (WTPS) on middle-Eocene carbonates (MCARB), Pakistan. 18-Hz amplitudes detect the gas-bearing stratigraphic prospect of 230 km2 on the northern flanks. The 18-Hz-based WTPS has predicted the parasequences within the complete petroleum systems. 24 m thick progradational and laterally continuous and fractured reservoirs are deposited within the wet-gas-bearing zones (WGZ) throughout a rapidly falling sea and succeeding growth at 175 °F and 28% porosity pseudo-wells. Deposition of 15–20 m thick deep-marine transgressive shale has been completed throughout a rising sea level at a temperature of 125 °F and 12% poor porosity. There is a lateral change in the dense-fractured then low-velocity from 2.1 to 1.8 g/cc and 2670 to 1690 ms/s predicted by WTPS from the NE to SW zones of MCARB, which impacts the presence of 1.5 km of the regionally developed pure stratigraphic trap. The WGZ has a vertically resolved thickness of 24 m, which is appreciably above the resolvable magnitude threshold of 23 m. Hence, it implies that the extensive fall of sea level followed by the regional development of the accommodation space for the accumulation of WGZ carbonate stratigraphic units is at its accurate location within the sub-surface reservoir system. This workflow has robust consequences towards exploring petroleum systems, Onshore Pakistan. Hence, this workflow may serve as an exemplary move towards regional analogues aimed at world carbonate in extensional regimes.