Based on our study the following conclusions
The precursor grainstones experienced micritization, marine cementation, equant calcite cementation, and mechanical compaction before dolomitization (Fig. 13a; Bao et al., 2011). As burial progressively increased to about 760 m depth, dolomitization began and dolomite preferentially replaced the grain components in carbonates (Fig. 13b), but micritized grains with low permeability were not dolomitized (Fig. 13b). At this AS 1892802 stage, the porosity of rocks kept constant or slightly decreased due to external CO32− added. As the dolomitization proceeded, the texture of grainstones tended to be destroyed and accompanied by the formation of dolomite crystal framework (Fig. 13c). However, although the dolomite contents increase up to 90%, carbonate rocks still have very low porosity and permeability due to abundant remnant microcrystalline calcite in the interstices between dolomite crystals (Fig. 13c). When dolomitization process evolved into the stage III, the porosity increased significantly due to the dissolution of the remnant calcite. Moldic or vuggy pores resulted from the dissolution of micritized grains that resisted dolomitization at earlier stages (Fig. 13d). After limestones were completely replaced or dissolved in stage IV, dolomite cements precipitated in pores (Fig. 13e) from the subsequent dolomitizing fluid that preferentially migrated through porous dolostones. In addition, some dolomite cements are the byproduct of pressure solution of host dolostone (Wang et al., 2015a). The precipitation of dolomite cements resulted in a slight decrease in porosity, but significant in permeability in the Jiannan area.