2D Seismic Data Interpretation And Petrophysical Analysis Of Sawan Gas Field, Central Indus Basin, Pakistan

Abstract

The research focused on uncovering the subsurface geology of the Sawan area that lies in Khairpur district through seismic interpretation and assessing hydrocarbon saturation using petrophysical techniques. Seismic data interpretation played a pivotal role in this study, enabling a deeper understanding of the geological features beneath the Earth's surface. The area exhibits an extensional basin regime characterized by normal faults, clearly delineated in interpreted seismic sections from F1 till F10. These structural features, including horst and graben structures, are significant indicators of potential hydrocarbon accumulation zones. The Sembar Formation was identified as the primary source rock while the Lower Goru, Ranikot, and Sui Main Limestone formations act as reservoirs, with the Upper Goru serving as the seal rock in the petroleum system. The seismic analysis marked key horizons such as Lower Goru (Cretaceous age), Ranikot (Paleocene age) and Sui Main Limestone (Eocene age) for which time and depth contour maps were generated to map their distribution and structural characteristics. Petrophysical analysis focused specifically on the Lower Goru Formation to hydrocarbon-bearing zones based on log trends. The study provided average values for parameters crucial to hydrocarbon assessment in the Lower Goru Formation. Petrophysical analysis showed two zones within the Lower Goru Formation showing below par reservoir potential. Zone 1 exhibited 33.9% shale volume, 27.6% hydrocarbon saturation and 8.9% effective porosity indicating a moderate potential for hydrocarbon content. In contrast Zone 2 showed 42% shale volume, 33.5% hydrocarbon saturation and 5.7% effective porosity suggesting a higher hydrocarbon saturation, but lower effective porosity as compared to Zone 1. These findings highlight the heterogeneous nature of hydrocarbon distribution within the Lower Goru Formation where zone 2 having relatively more values of hydrocarbon saturation but depict high volume of shale with less effective porosities. Overall, the integration of seismic interpretation and petrophysical analysis in this research enhances the understanding of potential hydrocarbon reserves in the Sawan area.