<p>The unique geographical setting of the South China Sea has made it a natural laboratory for dolomite research within reef systems with its extensive reef carbonate sedimentary deposits. Well Xike-1 is a typical example of deep dolomite reservoirs in this region, featuring tight dolomite with low porosity and low permeability. It would be critical to understand the difference between such tight dolomite and conventional dolomite, both theoretically and practically. Multiple approaches were adopted in this study, including core observation, microscopy, scanning electron microscopy (SEM), major and trace element analysis, rare earth element (REE) analysis, and stable isotope (C, O) analysis. The results indicate that the target interval comprises residual bioclast dolomite and crystalline dolomite. These crystals range from silt-sized to fine-grained with subhedral to anhedral forms, and their contacts vary from point and planar to densely packed. Pores are mostly isolated without effective connectivity. The mineral phases mainly include calcite, dolomite and ankerite, with generally low concentrations of Mn and Sr and a relatively high Sr/Ba ratio. The high values and weak correlations of carbon and oxygen isotopes suggest low temperature and high salinity in the diagenetic fluid. The rare earth elements show typical marine patterns, with negative Ce anomalies and weak positive Eu anomalies. It can be concluded that the dolomite in the target interval was developed in a marine-sourced, high-salinity lagoon environment, where the diagenetic setting and processes determine its reservoir properties. Diagenesis of the dolomite in the region occurred in multiple stages under relatively closed conditions. In this process, overdolomitization led to multi-phase alteration by contemporaneous dolomitizing fluids, which filled the pores formed at earlier stages and ultimately led to reservoir densification.</p>