The Numerical Simulation Of The Evolution Mechanism Of Brine Under The Supplyment Of Humans

Because of the abundant mineral resources,the Qaidam Basin is known as the cornucopia of China.The Kunty salt flats,located in the northwest of Qinghai province,is a sub-basin of the Qaidam Basin.It is a comprehensive salt ore deposit with kinds of minerals.At present,the exploitation of the liquid potash is dominant.The brine exploitation in Kunty Salt Lake began in 2004,with the increase of the market demand of sylvite,the scale of production is also expanding.The exploration of brine has become more and more difficult because of the expanding production scale.In order to solve the problem exist in the process of the brine exploration,an artificial water supplement has channel into the Kunty Salt Lake in July,2013.The supplement water is the water of Sugan Lake,and its degree of mineralization is much lower than the brines,which make the supplement water like a fresh water.Therefore,the supplement water permeate into the matrix,and dissolved the minerals in the matrix,then make the structure of the stratum changed,the collapse of ground happened frequently.In addition,the exploration of brine is focus on the western of the study area,this lead to a landing hole existed in this place,with the continue of the exploration,the area of the landing hole became bigger and bigger.Even though the human activities take much destroy to the environment,the quantity and quality of brine is kept decline.In order to solve the problem exist in the brine exploration in current,and protect the environment,we need to formulate a better exploration plans,make the sources of brine can be utilized effectively.Based on the field sample collection and indoor test,we explored the water level and chemical dynamic mechanisms of the intercrystalline brines in the Kunty Slat Lake,and analyzed the current situation of the brine under the influence of the human activities.The method of mathematical statistics is used to establish the model with time,spatical variation of brine level to explore the feasibility of this simulation,and determine the anomalous area of the ore deposition.Using the GMS simulation software,which is widely used in the geology,to predict the water level and chemical migration,and make a better exploration plain according to the conclusions above.The dynamic changes of brine in Kunty Slat Lake need to be preliminarily understood before the simulation analysis.Using the surfer software to draw water level and ion concentration contour map.The results show that the average water level values of observe boreholes has not changed very much in the past two year.The distribution feature of the brine water level is characterized by a high level in the northeast and a low level in the northwest.The center of the landing funnel is located near the factory area,in the western of the region,and is gradually expanding.The highest water level appears near the F₅ fault,this indicate that the fracture may be the channel for underground runoff.The distribution characteristics of ion concentrations are related to the minerals contained in the strata.The concentrations of K⁺,Mg²⁺and SO₄^2-are low in the northeast and high in the southwest,while the concentrations of Cl^-and Na⁺are high in the northeast and low in the southwest.The concentration of Ca²⁺is not obvious in the mining area.The change of ion concentration in time has played a seasonal periodicity,this should be affected by the change of solubility of the mirabilit.Compared with the change of ion concentration,it is believed that there are frequent water-rock transformation in the formation of the Kunty Slat Lake.The reaction minerals are mainly halite,followed by gypsum,potassium and mirabilit.Through the results of the rules of dynamic change of the brine water level and chemical,we consider that the artificial freshwater supplement is an effective method in help to improve the"quality"and"quantity"of the brine,but this also caused the increase of formation permeability,the damage of the human activities take to the stratum structure also cannot be ignored.In order to get a further understanding of the formation mechanism of brine,an analysis of boron isotopic composition and ion concentration has been used to explain the originate of the in tercrystalline brine in Kunty Salt Lake.The result shows that the brine mainly influenced by the evaporation,and the dissolve of halite supplied most of the mineral sources of the brine.The water sources of brine are mainly from the water of Sugan Lake and the hydrops of alluvial fan.The effects of deep mantle and snow melt are uncertain.After the exploration of the dynamic change mechanism of brine,time series model and trend surface analysis were used to establish a statistical model for the brine water level of Kunty Salt Lake.The fitting accuracy of time series model is just qualified,and the fitting accuracy of cubic polynomial trend is just 0.65.The trend of water level in the future year predicted by the time series model is consistent with the current change trend,which shows the gradual decrease and the predicted annual decrease of 1.5 m.After the simulation data has been collected,the MODFLOW module and MT3D module in GMS are used to simulate the water level and solute migration of the brines in the Kunty Salt Lake.The whole area is generalized into three aquifers,namely the confined aquifer and the diving aquifer,and the intermediate water layer in the middle will be reduced to a micro-permeable layer.Then,the boundary conditions are generalized and the source sinks are processed.The aquifer is generalized into an isotropy,heterogeneity,unsteady flow.In the process of modeling,both the brine channel and the water supply canal are generalized to the well flow pattern.The nine stress periods are set,and the stress period is 60 days.The data of the previous eight obverse were used to adjust the parameter,and the last data regard as the proofread data.The result shows that the numbers of observation water level error within 1m was up to75%,and the simulation accuracy was better.In the solute migration simulation,the effect of solid liquid conversion is reduced to the adsorption reaction,and the ideal result is obtained.The simulation of brine water level did not achieve better fitting results,mainly because the effect of water-rock conversion during the water migration is ignored.During the simulation,the permeability coefficient of each stress period was found to change.Therefore,we consider that the effect of the water-rock conversion should taken into account with the change of parameters over time.Through the analysis of the intercrystalline brine dynamics rules in Kunty Salt Lake,and combined with the result of simulation and forecast,a new exploration area was confirmed in the southeast of the ore deposition.According to the wheel tightly and fill mining separation scheme which designed after the simulation result,we hope to increase production of potash,avoid landing loopholes to further expand,and built a sustainable development of the brine mining environment.