Reactive Solute Transport In Single Granitic Fractures

In underground rock engineerings such as underground crude oil storage,rock fractures are the main sites for the occurrence and movement of groundwater.When underground water flows through the rock fractures,The effect of convection can cause solute migration,and at the same time,the solutes in groundwater can react with minerals in the rock fracture surface,which involves a substance transfer process,i.e.,reactive solutes transport in fractures.The process will lead to the change in the mineral composition and microstructure of the surrounding rocks,which will have an irreversible effect on the permeability and stability.This study is based on the first large-scale underground crude oil storage in China.The field monitoring,theoretical analysis,laboratory tests,and numerical simulation methods are used to analyze the characteristics and causes of groundwater chemical evolution,the connectivity between groundwater,and the the effectiveness of water curtain system in it.And later combine reactive solutes transport experiments in a single granite fracture with different Reynolds numbers with the numerical simulations to study the reactive solutes transport characteristics in a granite fracture and the influence of groundwater flow on the chemical reaction rate of water rocks.The specific results are as follows:(1)Based on the first large-scale underground oil storage in China,it can be found that there are two main factors influencing the chemical characteristics of groundwater in the underground underground crude oil storage,namely groundwater seepage and the chemical reaction between underground water with the surrounding rocks by on-site monitoring,mineral composition analysis and mathematical statistics analysis,;at the same time,it can be seen that the water of the water curtain system can fully infiltrate into the underground to form a water curtain to prevent the leaking of the oil.(2)A set of equipment that can simulates the reactive solutes stransport in a rock fracture was designed and developed.This equipment can simulate the water-rock chemical reaction and the reactive solute transport under real conditions of fracture.it can be used to do experiment under different flow regimes.(3)Experiments of reactive solutes transport in a granite fractures under different Reynolds numbers were carried out.The study indicates that convection has the biggest effect on solute transport,followed by dispersion,and the least impact on the chemical reaction of water-rock during the reactive solute transport experiments in granite fractures.Since the change of the concentration of solute in the process depends on the slowest controlling factor,the water-rock chemical reaction is the most critical point that influences the change of ion concentration.At the same time,the most important water-rock chemical reactions in this process are CaAl2(SiO4)2+8H+?Ca2++2H4SiO4+2Al3+,Al3++3H2O?Al(OH)3?+3H+ and H1O+CO2(?)H2CO3(?)HCO3-+H+.At Re=500,the dissolution rate of anorthite is faster,and more effective on the dissolution rate of anorthite then at Re=2500.(4)A reactive solutes transport model was established with COMSOL Multiphysics.comparing the numerical analysis results with the experimental data,it can be seen that the experimental data and the numerical simulation results are consistent during the entire migration process.