Experimental Research On Corrosion Spreading Characteristics And Mechanism Of Carbonate Rocks

Karst is not only the space where resources exist,but also the place where disasters occur.Its inhomogeneity and complexity bring many difficulties to the development and utilization of resources and related engineering construction.It is an effective way to solve these problems to simulate and reproduce the development process of Karst by means of the corrosion expansion model.The selection of parameters of the corrosion expansion model,especially the parameters of the corrosion rate equation,is an effective way to solve these problems.The simulation of karst system is very important.In order to determine the parameters of dissolution rate equation,based on the theory of carbonate rock dissolution expansion,a solid model of carbonate rock single fracture dissolution expansion and carbonate rock fracture network dissolution expansion is designed and developed.The seepage-solution coupling test of carbonate rock single fracture surface under open system and the fracture seepage-dissolution at the intersection of carbonate rock passage and mouth fracture under closed system are carried out.The following conclusions are drawn from the coupled laboratory tests:The larger the thickness of water film flowing downstream through a single fracture on the surface of carbonate rock,the larger the initial average dissolution amount and the larger the average dissolution rate.The change of water film thickness is about 1.5 times,the change of initial average dissolution amount is about 1.5 times,and the change of average dissolution rate is 1.43-2.04 times.The higher the concentration of CO₂ in single fracture flow,the higher the dissolution rate of carbonate rocks.The average dissolution rate of supersaturated CO₂flow is about 1.84-2.36 times higher than that of distilled water flow.Ca²⁺concentration in single fracture flow has a certain inhibitory effect on dissolution expansion.The higher Ca²⁺concentration in a certain range,the smaller the dissolution rate of carbonate rocks,and the trend of dissolution curve of carbonate rocks with Ca²⁺flow is different from that of distilled water.The higher the velocity of water flow and the lower the initial instantaneous dissolution,the faster the average dissolution expansion rate of the fissures in the carbonate network under the closed system,which has no obvious effect on the total dissolution.The head difference of seepage water in fracture network varies twice,the initial instantaneous dissolution amount varies 0.6 times,and the average dissolution expansion rate varies 1.48 times.The higher the partial pressure of CO₂ in the flow of fracture network,the higher the rate of carbonate rock corrosion expansion.Compared with distilled water seepage,the initial instantaneous solubility and total solubility of supersaturated CO2 flow change about 3 times and 2.62 times respectively.The higher the concentration of Ca²⁺in seepage flow in fracture network,the smaller the total dissolved amount.The concentration of Ca²⁺in water flow changed twice and the total dissolved amount changed 0.63 times.The rate equation of carbonate rock dissolution is validated by the single fracture corrosion expansion test and the fracture network corrosion expansion test,especially in the low-level rapid dissolution reaction stage.Through the test results,the parameters of the carbonate dissolution rate equation can be calculated.The relationship between c₁ and c_eq,c₁=0.4ce_q,and k₀,k₀≈1×10^-7m/s,can be obtained.