Simulation for the dissolution mechanism of Cambrian carbonate rocks in Tarim Basin, NW China

Carbonate dissolution during the process of burial and evolution by percolating acid fluid was simulated using core plugs to analyze the characteristics and controlling factors of Cambrian carbonate rock dissolution in the Tarim Basin. The results showed that mineral composition and reservoir space type control selective dissolution. In the carbonate rock strata with high calcite content, the calcite is likely to dissolve first to form secondary dissolution pores; gypsum and anhydrite in the carbonate rock can be dissolved to form mold pores in contemporaneous and penecontemporaneous stages. Porous carbonate has mainly enlargement of matrix pores, with porosity and permeability increasing correspondingly, but not obviously. In comparison, dominant channels for fluid are likely to occur in fractured carbonate or porous carbonate forming cracks under high pressure, resulting in a relative reduction in the dissolution volume, but great increase of permeability. With the rise of temperature and pressure, corrosion ability of acid fluid to carbonate rock increases first and then decreases, there exists an optimum range of temperature and pressure for dissolution, which corresponds to the buried depth of 2 250−3 750 m of the Cambrian. Considering reservoir characteristics of the study area, it is concluded that calcite in the penecontemporaneous period is the material basis for the development of dissolution pore, and carbonate rock were mainly dissolved by early atmospheric fresh water, superimposed and reformed to form high quality reservoirs by multiple acid fluids including deep hydrothermal fluid and acid fluid generated during the process of organic thermal evolution under burial condition.