Carbonate seismic sedimentology: A case study of Cambrian Longwangmiao Formation, Gaoshiti-Moxi area, Sichuan Basin, China

Abstract

This study applied seismic-sedimentological workflow to deeply buried marine carbonate sequences in western China. The workflow aimed at integrating core, wire line log and 3D seismic data to investigate the paleogeomorphology qualitatively and reservoir thickness quantitatively in the carbonate systems. In Gaoshiti-Moxi area of Sichuan Basin, the Longwangmiao Formation was formed in sedimentary environment of carbonate platform facies. Lithofacies vary from dolomitized grainstone to mudstone, which formed shoal, lagoon, and deep shelf sub-facies. The high-porosity (porosity > 4%) reservoir rocks are related to shoal sub-facies. Seismic geomorphology was employed to restore paleostructure of Longwangmiao Formation in the study area by methods of cast and isopach, which were calibrated by well data. It was found that the paleogeomorphology and depositional facies were largely controlled by a syndepositional, en echelon fault system. Following the strategy of seismic lithology, quantitative distribution of reservoir rocks and sedimentary facies was assessed by applying principle component analysis on amplitude attributes generated from multiple frequency panels. Seismic prediction of diagenetic facies (selective dissolution) was achieved by interpreting similarity variance, a seismic geometric attribute. In summary, the procedure, combining seismic geomorphology and seismic lithology, is effective and can be used as a reference for seismic-sedimentological study in other carbonate basins in China and elsewhere. Key words: seismic sedimentology, seismic geomorphology, seismic lithology, seismic diagenetic facies, carbonates, carbonate platform, Sichuan Basin, Gaoshiti-Moxi area, Cambrian Longwangmiao Formation