Effect Of Stratigraphic Hydrochemistry On Diagenesis Of Clastic Reservoirs

Formation water participates in the main process of diagenesis.The result of the reaction between formation water and rock affects the diagenesis products and formation water chemistry.Formation water chemistry is one of the important influencing factors of diagenesis.In this paper,the combination of numerical simulation,core thin slice observation,and laboratory simulation is used to realize the diagenetic difference between NaHCO₃type water and CaCl₂type water reservoirs in the middle submember of the third member of the Shahejie Formation in the Central Uplift Zone of Dongying Depression.From the perspective of formation water ions and p H,the causes and main influencing factors of the differences in diagenesis between the two types of water reservoirs are analyzed and simulated.The reservoir with CaCl₂ type water has a high content of dolomite cement,the early calcite cement is basically dissolved,and the conversion of potassium feldspar to albite and clay minerals in plagioclase can promote the formation of illite and chlorite minerals.If there is aluminosilicate rock,the production of dolomite and iron dolomite cement is relatively reduced.The reservoir with NaHCO₃type water is mainly cemented by early calcite cement,the dissolution of potassium feldspar mineral is relatively reduced,and the clay mineral is mainly kaolinite.The results show that the difference between the two water reservoirs is affected by organic acid charging and formation water ion concentration.The organic acid filling time is earlier,which can dissolve the early calcite cement in the formation;the later organic acid filling is not conducive to the dissolution of the early calcite cement.Alkaline cations have the same ion effect and participate in diagenesis reactions;anions have a salt effect.Increasing or decreasing the anion concentration can affect the diagenesis reaction to a certain extent.Among them,SO₄^2-salt effect is stronger than Cl^-salt effect and the influence of HCO₃^-is controlled by the CO₂balance in the formation water.