The Impact Of CO₂Leakage From Reservoir On The Water Quality Of The Shallow Aquifer

The large quantities of CO₂emissions have caused global climate change and itis currently one of the hot topics in the international society. The CO₂geologicalstorage technology （CGS） is internationally considered as an effective way andcountermeasure to reduce CO₂emissions emitted to the atmospheres, CO₂storagemay cause a series of environmental safety problems. The researches show that theCO₂of deep reservoir may go through the hole of well, fault, fracture or othergeological structure into the upper reservoir of the shallow aquifer. Once the CO₂leaks into the shallow aquifer, it may changes the quality of aquifer water, whichthreatens people’s health who drinking the aquifer water and the security ofgroundwater ecosystem.Basing on the mechanism of CO₂geological storage and the project of numericalsimulation projects, the paper treats Ordos CO₂geological storage demonstration areaas the object of study. Combing with the site conditions and using the simulationsoftware TOUGHREACT, the essay builds the numerical simulation model of CO₂leaking into the shallow aquifer, prospective study the environmental impact of CO₂leaked into the shallow aquifer. And discussed influence of groundwater flow velocity,CO₂leak rate, mineral galena volume fraction, reaction of mineral surface parametershas be made.The conclusions are as follow:1. After CO₂goes into the aquifer, it will increase the acidity of groundwater andmake the mineral dissolute or precipitate and porosity, permeability change: Thequartz precipitate. Potassium, chlorite, feldspar, calcite, feldspar, Na-smectitedissolved. The Ca-smectite, illite dissolve at the location of the leak point andprecipitate precipitation in the downstream of the leak point. The kaolinite precipitation at the location of the leak point and dissolve in the downstream of theleak point. The mineral dissolution/precipitation affects the porosity, permeability arenot obvious.2. Under the condition of minimum leakage rate（0.0005kg/s）, the imitationchanges the aquifer groundwater environment: the pH decreases rapidly understandard of drinking water （pH range6.5⁸.5）; Ca²⁺concentration increases, whichincreases the temporary hardness of aquifer, making groundwater to be general veryhard water. Maximum Germanic degrees is136; the galena dissolves and theconcentration of Pb²⁺increases two orders magnitude above the initial value. Becausethe to the original number of galena in the stratum is low, the concentration of Pb²⁺isstill below the national drinking water standards.3. Model parameter sensitivity analysis results show that the groundwater flowvelocity, CO₂leakage rate, volumetric fraction of galena, galena reaction specificsurface area have significant effect on the simulation results. Groundwater flowvelocity decreased, the CO₂leakage rate increase, galena initial volume fractionincreased, specific surface area increases, lead to ground water hardness, Pb²⁺concentration exceed the national drinking water standards.4. On the basis of foundation scheme, design the6kinds of scheme ofquantitative analysis of the groundwater flow velocity, CO₂leakage rate, volumetricfraction of galena, galena reaction specific surface area the influence of water qualityin aquifer. Groundwater velocity reduces by half, the rate of leakage of CO₂increase2.4times, groundwater hardness generally increases30Germanic degrees. Galenavolume fraction, specific surface area increase an order of magnitude, lead ionconcentration of groundwater increases by an order of magnitude.