Hydrothermal Process Features and Formation Mechanism of Middle-Lower Ordovician Dolomite Reservoir in Tadong Area

Hydrothermal process is common in the Middle-Lower Ordovician carbonate reservoirs in Tadong Area, which is an important diagenetic process for reforming reservoirs, and the hydrothermal dolomite reservoir which formed is an important exploration direction.Through core observation, rock thin section identification, cathodoluminescence, stable isotopes of carbon and oxygen, trace elements and rare earth elements, the identification markers of rock mineralogy and geochemistry were established and the formation mechanism was discussed. The hydrothermal action in the study area can be divided into two stages. The hydrothermal action in the first stage is characterized by the development of multiple types of dolomite, and the cathode luminescence is characterized by no luminescence or dark luminescence; In the second stage of hydrothermal process, the dissolution fissure was developed, saddle-shaped dolomite or calcite was filled, and the cathode luminescence was orange. The geochemical characteristics of the hydrothermal dolomite of the two stages have a good matching, the diagenetic fluid of the stage I medium-coarse crystal dirty dolomite and the stage II medium-coarse crystal dirty dolomite comes from the basic magmatic hydrothermal fluid, while the diagenetic fluid of the the stage I medium-coarse crystal cleaner dolomite comes from the acidic magmatic hydrothermal fluid. The hydrothermal process in the first stage mainly used micropores as hydrothermal flow channels to reform the Middle-Lower Ordovician strata in the study area, In the second stage, due to the strong brittleness of dolomite, irregular hydrothermal rupture and dissolution occurred, which were distributed in the vicinity of tectonic fractures and the dissolution fractures were relatively developed. These locations may be favorable reservoir development zones.