“Seismic attributes and reservoir simulation’ application to image the shallow-marine reservoirs of Middle-Eocene carbonates, SW Pakistan”

Abstract

Carbonates form brilliant stratigraphic traps. The execution of traditional seismic data interpretation using time and depth mapping generates ambiguities in the discrimination of porous and non-porous reservoir beds. In these stratigraphic circumstances, placement of development wells within the unproven prospects is a trial for exploration geophysicist. The 3D post-stack seismic attributes and quantitative seismo-petrophysical simulation (QSPS) are applied on Habib Rahi Limestone (HRL) Member from a gas field, SW Pakistan. 45 Hz spectral magnitude delineates the lithology, fractures, and geomorphology of gas-bearing shoal reservoir facies than full-spectrum seismic tools. 45 Hz predicts a north-east oriented gas-bearing stratigraphic lead, which covers an area of 105 km2. The QSPS reveals a very low-density (2–2.1 g/c.c.) and low-velocity (~2500–3000 m/s) of shoal reservoir. The high-quality shoal limestone reservoirs of HRL with ~30% porosity are deposited during the regression phase of sea-level fall in the east. The low-quality fine-grained seal facies with <9% porosity are deposited during the substantial transgression phase of sea-level rise in the west. The cross plots of seismic-based porosity (%) versus inverted velocity (m/s), inverted density (g/c.c), and reservoir thickness (m) show correlation coefficients of (R)2>0.92, (R)2>0.97, and (R)2>0.89. The coarse-grained gas-bearing reservoirs experience 31.8 m thickness and least density (2–2.1 g/c.c.) are deposited during sea-level fall. The 31.3 m thick and high-density (2.2–2.3 g/c.c.) fine-grained seal facies are deposited during sea-level rise. This workflow can serve as an analogue for the development of carbonate fairways within Asia and similar world basins.