Spectral decomposition-based static reservoir simulations image Cretaceous hydrocarbon-bearing incised-valley, Southwest Pakistan

Abstract Incised valley sandfills are globally renowned for forming excellent stratigraphic traps. These incised valleys are developed during the extensively falling stage of the sea, followed by a negligible rise, which fills the incised valleys with coarse-grained reservoir facies. However, sea-level fluctuations cause fluctuations in the lateral distribution of the reservoir. Hence, it becomes very difficult to simulate the exact thickness, impedances, and lateral phase changes. Hence, these might act as direct hydrocarbon indicators (DHI). Therefore, this study applies the state-of-the-art spectral decomposition and static acoustic impedance reservoir simulations tool to determine the thin-bedded reservoirs within a stratigraphically complex unit for implicating the future well drilling strategies for the known gas field of Indus Onshore, Pakistan. The key emphasis was given to the selection and optimizations of the spectral waveform-based simulations. The outcomes of these simulations were to develop strategies for horizontal well drillings. The stratigraphic traps are NNW-SSE oriented with localized transpressional fault-controlled components. These fault-controlled components have played a vital role in the upward migration of hydrocarbon-bearing reservoir facies. The 21-Hz, 29-Hz, and 41-Hz tuning blocks outline the hydrocarbon-bearing sand-filled reservoir facies inside the Lowstands system tract (LST). The 57-Hz tuning block recognizes the transgressive seal facies at the top of the LST. The bandlimited static reservoir model (SRM) shows some noise events within the sedimentary reflections. The 21-Hz spectral wavelet-based developed SRM has enhanced the signal-to-noise (S/N) ratio for imaging a 34 m thick sand-filled lens. Consequently, this study serves as an analog for global shallow-marine incised valley systems.