Experimental Study On Hydrochemical Changes In Granite-water Reaction

A large number of earthquake cases showed that the changes of composition of groundwater could be observed before and after the earthquake.In this paper,the experiments of granite-water reaction under differential stress were used to simulate the changes of hydrochemical components of granite aquifers during stress accumulation to fracture of rock,and the influence of hydrochemical type,time and temperature on the hydrochemical composition of granite-water reaction was explored through the soaking experiment,thus genetic mechanisms of hydrochemical anomalies related to earthquake were discussed.The results of high pressure experiment showed that the concentration of different ions in the solution increased in varying degrees with the increasing of stress loading time and differential stress.The concentration of Na⁺,K⁺ and Cl-was obvious.With the increasing of differential stress,the maximum value of the concentration of the three ions increased to 3.3,2.5 and 11.5 times that of the initial solution respectively,and with the increasing of stress loading time,the maximum value of the concentration of the three ions increased to 3.2,3.1 and12.5 times that of the initial solution respectively.These changes were mainly due to the effect of microcracks in the rock produced by differential stress and the continuous development of the micro fissure,which increased the contact area of water-rock reaction,and also could be related to the fluid inclusion in the rock.The results of the atmospheric pressure soaking experiments showed that the changes of ionic concentration were related to soaking time,temperature and chemical composition of water.In different hydrochemical types,with the increasing of soaking time and temperature,the changes of ion concentration were different.K⁺ and Cl-were significantly influenced by soaking time and temperature in Ca·MgHCO₃ type.Ca²⁺ and Cl-were significantly influenced by soaking time in Na·CaHCO₃ type,while K⁺ and Cl-were affected by temperature.Ca²⁺ and Cl-were significantly influenced by soaking time in Na-SO₄·HCO₃ type,while K⁺,Mg²⁺ and Cl-were affected by temperature.Among them,the concentration of Cl-in three hydrochemical solutions changed obviously with the increasing of soaking time and temperature.These changes were mainly due to the dissolution reaction of minerals.All the experimental results showed that the changes of the concentration of Clin granite-water reaction were most obvious,which could be mainly related to the dissolution of the black mica and apatite.Cl-could be used as sensitive components for monitoring precursors of seismic hydration of granite aquifers.