Formation mechanisms and development models of dolomite reservoirs in Ordovician Yingshan Formation in Shunnan area, Tarim Basin

Abstract

The dolomite reservoirs of the Ordovician Yingshan Formation in Shunnan area of the Tarim Basin have a great oil and gas potential. However, the genesis of different types of dolomite reservoirs is still subject to debate. In order to further deepen the understanding of the dolomite reservoirs in Shunnan area and clarify the genesis and development models of the dolomites in the Ordovician Yingshan Formation, the petrography and geochemistry of the dolomites were studied in detail, and some dolomitization models were established based on observation of core samples and thin section identification, using SEM, cathodoluminescence, carbon and oxygen isotope data and rare earth element pattern analysis. The petrographic analysis shows that the Yingshan Formation mainly develops three types of dolomite: powder-fine crystalline dolomite, fine-medium crystalline dolomite and fractured vug filling medium-coarse crystalline dolomite. Geochemical characteristics reveal that powder-fine crystalline dolomite is formed in water with higher salinity, which is the product of near-surface environment evaporation pump dolomitization. Fine-medium crystalline dolomite is formed in a buried environment. Medium-coarse crystalline dolomite is formed in relatively closed diagenetic environment, which is the product of tectonic-hydrothermal dolomitization.Medium-deep buried dolomitization can form large-scale fine-medium crystal dolomite with well-developed pores, which is the most favorable dolomitization for reservoir development.

Keywords

• dolomitization
• geochemical features
• carbonate rock
• yingshan formation
• ordovician
• tarim basin