Dissolution Mechanism Of Limestone And Evolution Of Surface Morphology Under Water Rock Interaction

In order to study the dissolution mechanism of limestone and the evolution of rock surface morphology under water rock interaction,this paper takes the typical limestone in the Shuibuya reservoir area as the research object,and carries out the three-dimensional surface topography scanning test,solution ion concentration detection and hydrogeochemical simulation of rock samples under different water rock interaction time.The main research contents and research results are as follows:(1)Conducting mineral dissolution-precipitation tests under water and rock interaction,selecting hydrochloric acid solution(0.01,0.03,0.05 mol/L),sulfuric acid solution(0.002,0.004,0.008 mol/L),potassium chloride solution(0.01,0.03,0.05mol/L)soaked limestone in the water storage area,and analyzed the variation of ion concentration in different solutions under different water and rock action time.The results show that during the water rock interaction of the three solutions and limestone mineral,the most obvious cations in the solution are Ca²⁺and Mg²⁺,and the anion is HCO₃^-.The process mainly involves the dissolution of calcite and dolomite,which makes Ca²⁺and Mg²⁺in the rock sample are precipitated while generating HCO₃^-.(2)The PHREEQC software was used to simulate the equilibrium of limestone under water rock interaction by titration model.The effects of different ions,temperature,PH and CO₂ partial pressure on the dissolution-precipitation of limestone were studied.The reverse path simulation of the reservoir water-rock interaction was carried out by using PHREEQC software to study the process of water and limestone water from the starting point to the end point.The results showed that 8 common anions and cations were added,and the addition of K⁺,Na⁺and Cl^-had no effect on the dissolution-precipitation reaction of limestone minerals.The addition of Ca²⁺inhibited the dissolution of calcite.The addition of Mg²⁺changed the dolomite from the dissolved state to the precipitated state,the increase of CO₃^2-and HCO₃^-content inhibited the dissolution of calcite and dolomite.The addition of SO₄^2-increases the dissolution of calcite.With the increase of temperature,the dissolution of calcite and dolomite showed an upward trend.With the increase of PH of solution,the dissolution of calcite and dolomite showed a downward trend;the dissolution of calcite and dolomite increased with the increase of CO₂ partial pressure.The saturation index of both the calcite and the dolomite in the reverse path simulation end point increased significantly,indicating that the two minerals dissolved in the simulated path.The water rock interaction between the reservoir water and the limestone is mainly the dissolution of calcite and dolomite.(3)The three-dimensional morphology of the limestone surface was scanned to study the variation of the three-dimensional morphology of the limestone surface under different water rock interaction time.The results show that after the water and rock interaction,the dispersion of the surface topography height,the degree of deviation from the reference surface,and the roughness degree become larger.The symmetry of the surface height distribution is better than that before water rock interaction,and the distribution probability of the surface height is more concentrated than that before water rock interaction.The surface height of the rock sample changes more and more obviously,and the isotropic characteristics of the rock sample become weaker and weaker,and gradually change to anisotropic characteristics,while the surface shape of the rock sample does not change in the direction of the undulation and the direction of the texture extension.After water and rock interaction,the surface roughness of the rock sample increases,and the degree of surface roughness is more complicated than that before the water rock.