Influences Of Dongli Lake Water Reinjection In Tianjin City On The Scaling Characteristics Of Geothermal Reservoirs In Wumishan Formation,Jixian System

As a new type of green clean energy with huge development and utilization potential,geothermal energy has many advantages,including wide distribution,large reserves,good stability,and high utilization factor,etc.Geothermal resources are divided into two parts:direct use and power generation.Currently the main use method is direct use,such as heating,hot spring bathing,tourism,aquaculture,greenhouse cultivation,etc.The rational development and utilization of geothermal energy to reduce the use of fossil fuels is of great significance for improving the energy structure,improving the ecological environment,and promoting the sustainable development of society.Tianjin was one of the earliest city in China to develop and utilize geothermal energy.Wumishan formation in Jixian system is rich in geothermal reservoir resources and has a long history of development.Although Tianjin has actively carried out recharge work,the extraction volume is still greater than the recharge volume,which has caused the groundwater level to continue to decline.In order to make up for the imbalance of extraction and irrigation caused by years of mining,Tianjin tried to recharge with the surface water of Dongli Lake.When the surface water of Dongli Lake is recharged into the reservoir,the physical mixing between surface water and groundwater,and the interaction between surface water,groundwater and rocks will cause changes in groundwater quality,and also cause chemical blockage of recharge facilities or recharge layers problem.In this paper,taking the surface water recharge of Dongli Lake into Tianjin wumishan formation in Jixian system as an example,the effects of surface water recharge are explored through a combination of water quality static compatibility experiments,water-rock interaction experiments,and hydrogeochemical simulations.The research results provide a scientific basis for the sustainable utilization of geothermal energy in Tianjin.By predicting the scaling of surface water and geothermal water in Wumishan formation,the types of scales that may be generated in surface water and groundwater are determined,which provides an analytical basis for the static compatibility experiment of water quality.Through static compatibility experiments,explore the scale type and the amount of scale in mixed water with different proportions?1:9,3:7,5:5,7:3,9:1?at normal temperature and reservoir temperature?90??.The static compatibility experiment results were analyzed by scaling ion analysis.The theoretical and experimental results show the same:carbonate is the main scaling product;the amount of scaling at 90°C is larger than normal temperature;when the mixed water ratio is 1:9,the scaling is the smallest.Carry out experiments on interaction between different recharged water bodies?suface water,geothermal water in Wumishan formation,mixed waters with less scaling?1:9,3:7,5:5??and rocks,explore the water-rock reactions that occur between different water bodies and rocks,and the rules of hydrogeochemical action.The experimental results show that:On the whole,the larger the proportion of surface water,the more the Ca²⁺and Mg²⁺decrease,indicating that the precipitation is more likely to occur;the larger the TDS in the recharged water,the more likely it is to occur.When the ratio of surface water to geothermal water in Wumishan formation is 1:9,the precipitation amount is the smallest.Ca²⁺content is abnormal,showing an increasing trend,indicating that this ratio is most suitable for recharge;there is the phenomenon of dolomite,NaCl precipitation.The TOUGHREACT program was used to fit the experimental results of water-rock interaction to correct the reaction kinetic parameters.Using the corrected reaction kinetics parameters,a one-dimensional intermittent recharge model was established to predict the effect of different recharge water bodies on reservoir permeability and mineral dissolution and precipitation after 50 years of intermittent recharge conditions.The results show that when the recharge ratio is 1:9,the average permeability of the reservoir increases;when the recharge ratio is 3:7,the recharge ratio is 5:5,and the surface water recharges,the average permeability of the reservoir decreases,and as the surface water increases,the average permeability decreases.It is concluded that 1:9 is the most suitable recharge ratio;except for the 1:9 recharge ratio,the more surface water,the more disadvantageous it is for recharge.Permeability changes at different distances show that the greater the proportion of surface water,the wider the range of precipitation;the maximum permeability occurs at the wellhead,indicating that the water chemical composition of different water bodies has a particularly obvious effect on the wellhead,and the minimum permeability occurs at 105m;in the same water body and the same location,the longer the time,the greater the range of permeability change,and the more obvious the change trend;at the same time,at the same location,the greater the ratio of surface water,the more obvious the change in permeability.Changes in the mineral volume at different distances indicate that calcite and magnesite precipitated and dolomite dissolved after recharge.Within the range of 0³5m,calcite precipitation and dolomite dissolution are obvious,and magnesite precipitation is obvious in the range of 35⁷00m;in the same water body and at the same location,the longer the reaction time,the greater the precipitation of calcite and magnesite,and the greater the dissolved amount of dolomite;at the same time,at the same location,the greater the proportion of surface water,the greater the amount of calcite precipitation and the greater the amount of dissolved dolomite;in the range of 0¹80m,at the same time and the same location,the greater the proportion of surface water,the smaller the magnesite precipitation,in the range of 180⁷00m,the larger the proportion of surface water,the greater the amount of magnesite precipitation.The effects of different temperatures,different pH values,different CO₂ partial pressures,and different initial water chemical components on the dissolution or precipitation of carbonates were analyzed using hydrogeochemical simulation methods.The results show that the higher the temperature,the easier the dolomite to precipitate;the greater the CO₂ partial pressure,the greater the dolomite solubility;the lower the pH,the easier the dolomite to dissolve;the higher the Ca²⁺and Mg²⁺content,the smaller the dolomite dissolution,the more dolomite precipitate.In summary,the laboratory experimental methods,numerical simulation techniques and hydrogeochemical laws under the recharge conditions explained in this research can provide theoretical basis and technical support for the sustainable development and utilization of deep karst geothermal in Tianjin.