Study on the law of elastic parameters of carbonate rock under differential burial history and diagenesis

Abstract

There are some high-quality reservoirs of internal dolomite within the Ordovician Majiagou Formation in the Ordos Basin, located in western China. However, influenced by sedimentary environments and differential diagenetic processes, these high-quality dolomite reservoirs exhibit thin sedimentary thickness and relatively small differences in elastic parameters compared to the surrounding rocks. Identifying these reservoirs using seismic data presents a significant challenge. In the study area, systematic sampling was conducted, and the physical and elastic properties of dolomite, limestone, and anhydrite were tested in the laboratory. Through various analyses, including physical property tests, thin-section observations, and CT scans, researchers discovered that the carbonate rocks in the study area underwent complex diagenetic evolution. The primary constructive diagenetic processes include dolomitization and dissolution; while the main destructive diagenetic processes involve compaction and cementation. Dolomitization leads to abundant intercrystalline pores, increasing rock porosity. The pore aspect ratio is relatively large, with predominantly near-circular pores. Additionally, because the longitudinal wave velocity of dolomite minerals exceeds that of calcite, dolomitization enhances the rock’s elastic parameters. Dissolution primarily alters pore shape, increasing rock porosity while reducing the aspect ratio of pores (mainly flattened pores). Consequently, this decreases the rock’s elastic parameters. Different diagenetic processes significantly impact the elastic parameters of the rocks. By analyzing the differences in elastic parameters before and after various diagenetic processes, researchers can clearly define the elastic parameter characteristics of high-quality dolomite reservoirs, providing a foundation for reservoir prediction in the study area.

Graphical abstract

Keywords

Ordos Basin / carbonate rocks / diagenesis / dolomitization / dissolution / pore structure

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