Experimental Study On The Influence Of Diagenetic Fluids And Rock Components On The Quality Of Mixed Sedimentary Rock Reservoir

The mixed sedimentary rock refers to a type of sedimentary rock that is mixed with siliciclastic sediments and carbonate rock,and has gradually become a focus in the study of middle and deep reservoirs in China,and deep reservoir research has important academic and oil and gas strategic significance.Based on the summary of the reservoir characteristics in the study area,this paper used collected data combined with water-rock simulation experiment,and applied scanning electron microscope,X-ray diffraction,ion concentration testing and other methods,to explore the process and mechanism of interaction between different diagenetic fluids and mixed mineral systems.It provided direct evidence for the formation mechanism of the mixed sedimentary rock in this area,and has practical guiding significance for the later fluid modification of the mixed sedimentary rock in other areas.The dissolution of the reservoir in the study area is mainly the selective dissolution of carbonate cements and feldspar by atmospheric water and deep thermal fluids such as organic acids and CO₂.The dissolution of the mixed sedimentary rock dominated by bioclastics is mainly the dissolution of dolomite in the cavities of gastropods and ostracods and the dissolution of dolomite between the bioclastics.The dissolution of mixed sedimentary rock dominated by terrigenous clastics is mainly granular dissolution pores and intergranular dissolution pores.The reservoir space of the mixed sedimentary rock reservoirs dominated by terrigenous clastics is dominated by dissolution pores,followed by biological cavity pores,with a few intergranular primary pores.The reservoir space of the the mixed sedimentary rock dominated by bioclastics is dominated by biological cavities,followed by dissolution pores,with a small amount of intergranular primary pores.The study area experienced multiple diagenetic stages,and the first and second members of Shahejie Formation are mainly in the late diagenetic stage.The degree of dissolution of feldspar,litharenite,and carbonate cement is relatively high.Experiments show that organic acids,CO₂,and atmospheric water have varying degrees of influence on various minerals,and the influence on the main minerals in the masticated rock reservoir shows a trend of"organic acid>CO₂＞atmospheric water".Calcite is more soluble than dolomite,compared with other minerals,carbonate minerals are more sensitive to CO₂dissolution,and have a stronger degree of dissolution,and show selective dissolution under the action of three fluids;feldspar minerals also have a selective dissolution phenomena,which shows that the degree of dissolution of plagioclase is greater than that of potassium feldspar,and the relative dissolution rate of the two gradually decreases with the increase of temperature.For the two types of minerals,the calculation methods to characterize the dissolution rate and dissolution amount of the two types of minerals are designed respectively,the calculation shows that plagioclase is more soluble than potash feldspar at medium-low temperature,and the dissolution rate of potash feldspar increases with the increase of temperature;calcite is always more susceptible to acid fluids than dolomite.The experimental results show that during the syngenetic to early diagenesis stage,minerals have obvious selective dissolution.At this stage,the degree of dissolution of carbonate minerals and cuttings is relatively high.In the early to middle diagenesis stage,the dissolution of carbonate minerals is stronger,followed by feldspar.In the middle to late diagenesis stage,the degree of dissolution of feldspar and cuttings is stronger,and the degree of dissolution of carbonate minerals is getting weaker.The experimental results have a good match with the diagenetic stage and actual dissolution phenomena in the study area.