The Fluid Flow In Horizontal Salt Cavern Under Thermal-Hydraulic-Chemical Coupling

Salt rock is internationally recognized as the ideal medium to store energy.In our country,as a supporting project of West-East gas transmitting,the underground storage is mainly used to solve the emergency gas supply problem because of the season,climate change and accidents.At present,the foreign salt cavity is generally built in deep salt dome and they are mostly vertical storage.But the characteristics of the ore deposits in China are complicated.The number of gypsum layers are more,the single layer is relatively thin and the weak interlayer is relatively more.If we directly reference the building method of the vertical salt cavity,the cavity in our country will inevitably through more layers.In that way,not only the difficulty and complexity increases,but also the stability of the salt cavity in the later operation process will be affected.Based on building the storage by water-soluble method in the bedded salt rock deposit,the paper combines the experiment and numerical simulation to made a preliminary study of fluid migration in the dissolution process of building the cavity in horizontal salt under temperature-hydraulic-chemical coupling.The results of the study has certain reference value in engineering.The main results are generalized as follows:(1)Establish a similar three-dimensional cavity model which are similar to to the horizontal salt rock cavity and set up the experimental platform.The ?theory of dimensional analysis is adopted to establish the similarity criterion and determine the ratio between the model and the engineering.According to the similarity criterion and the similarity ratio in the model,the string parameters,and the water flow are confirmed.In order to observe the fluid migration in the experiment,the cylindrical body of model cavity is made of organic glass.The experimental process is same to the actual engineering.Do well preparation for the experiment.(2)Tracer experiment of fluid migration.Consider five kinds of conditions,they are different spaces between casing,water injection of flow rate,concentration of brine,circulation way and injection way.The fluid flow regularity and regional distribution of flow field are studied.It is concluded that the formation of rock-salt cavity flow field distribution is buffer diffusion zone,precipitation and convective diffusion zone and saturated zone.The buffer diffusion zone is the main area of gypsum dissolution.The convection diffusion zone is a mixture area of the high concentration brine with low concentration brine.The saturated zone is full of saturated brine,so this area of gypsum is almost not be dissolved.Based on the comprehensive evaluation of the five kinds of process,it is conducive to the construction of the rock-salt cavity with the casing interval of 20 m,the water injection flow rate of 150 m~3/h and the positive cycle manner.At the same time,the measures must be taken to controlthe upper solution reasonably in the practical engineering.In order to satisfy the requirement cavity stability and maximize the utilization of space of gypsum layers,the string system is designed in the lower levels of gypsum layers as far as the back plane meet the design requirements.The result of the experiment can make reference to the actual cavity process design.(3)The FLUENT numerical simulation of fluid flow in horizontal salt cavity under thermal,hydraulic and chemical coupling.Considering three conditions of the different space casing and water injection flow rate and circulation way.The distribution regularity of flow field,concentration field and temperature field are studied.The flow field distribution rule is concluded: the fresh water from the center tube is obviously move to the upper zone of cavity.The flow transport into the the buffer diffusion zone at the top of the cavity and then migrate along the wall.The flow velocity of the buffer diffusion zone is the maximum,the flow velocity of saturated diffusion zone is minimal and the flow velocity of convection diffusion area is middle.The rule of concentration field distribution: the concentration of the upper zone is lower than the concentration of the lower zone of the cavity and the brine concentration of the lower zone keep a high level,nearly reached the saturation concentration of brine.The changes of techniques have no effect on concentration field at saturated area.The rule of temperature field distribution is similar to the rules of concentration.Based on the three kinds of process of the distance between casing,water injection flow rate and circulation way,a comprehensive assessment issuggested.It is advantageous to the construction of the horizontal salt cavity when the casing interval is 20 m,the water injection flow rate is 150 m3/ h and the injection way is positive circulation.(4)The boundary research of the salt cavity.At the beginning of injection,the cavity fluid flow are mainly concentrated between the inlet and outlet.The disturbance of the fresh water is very small and full of high concentration brine in the left end.As the growth of the salt cavity,the height of dissolution at the inlet is significantly higher than that at the outlet.The dissolution height of the upper gypsum at the inlet is the maximum.From inlet to both ends of the cavity,the height of gypsum dissolution decreases.During 100 days,the shape of rock-salt cavity change from flat to wedge shape.With the dissolve going on,the velocity of the outlet is decreased obviously,but the rate of decrease reduce gradually.On the contrary,the concentration of the outlet is gradually increasing with time and then remain a relatively constant value.The change rule of the temperature is similar to the rule of concentration.