Seismic Characterization of the Carboniferous Karst System and Its Significance for Hydrocarbon Exploration in the Eastern Margin of the Pre-Caspian Basin

Abstract

Carboniferous carbonate strata in the eastern piedmont belt of the Pre-Caspian Basin have undergone multi-stage karstification, forming highly heterogeneous reservoirs with complex pore-vug-fracture systems. Taking typical blocks in this area as the research object, this study integrates core, logging, and seismic data, and adopts four advanced characterization methods: microscopic karst staging, multi-frequency seismic attribute fusion, paleotopographic restoration, and seismic reflection configuration analysis, guided by a three-phase karst evolution framework. The results show that Carboniferous karst exhibits obvious vertical differentiation and horizontal zonation, with well-developed surface rivers, underground rivers, and karst caves. Three paleogeomorphic units, namely highlands, slopes, and depressions, are identified. Karstification, coupled with tectonic activity, sedimentary facies, and source rock evolution, collectively controls hydrocarbon accumulation, establishing a “fault-controlled karstification and slope-dominated accumulation” model. This study clarifies Carboniferous karst development patterns and seismic response signatures, providing key theoretical insights and practical guidance for carbonate reservoir exploration in analogous piedmont thrust settings.