Study On Reconstruction And Utilization Of Old Gallery Salt Rock Cavern For Storage

The main function of the underground gas storage in salt rock is to balance gas peak regulation and coordinate the relationship of supply and demand.Now,peak load capacity of underground gas storage accounts for 2 to 3%of annual natural gas consumption in China,it is much lower than average level of foreign underground gas storage peak load capacity accounting for 11%of annual consumption.In recent decades,directional and horizontal docking well technology is widely used in solution mining for salt deposits.And there have formed more than 200 old gallery salt rock caverns by this means in Huai'an,Jiangsu province,Pingdingshan,Henan province,Yunying,Hubei province and Hengyang Hunan province.Old gallery salt rock caverns are reconstructed as gas storage cavern,which can shorten the cavity construction period,save the cost of building a new cavity,avoid the collapse of the weaken interlayer,and reduce leakage risk of natural gas from the interface between salt rock and interlayer.The advantages will greatly improve strategic energy reserve capacity in China.Consequently,investigations on availability and modification technology of old gallery salt rock caverns are of great significance and value.The brine in the discarded cavern has become a high concentration or saturated brine after a long-term dissolution,coupling of fluid field and concentration field in the cavity is a complex coupling problem.Thus,it is necessary to study the law of crystallization of high concentration salt solution and coupling effects of the HC in the cavity,further determine the theoretical foundation and evaluation method for the reconstruction of the gas reservoir of the salt rock.These works are of great significance to accelerate the construction of the reservoir in China.Based on the engineering application of reconstruction of the gallery salt rock cavern in bedded salt deposits,investigations on physical and numerical simulations of the crystallizing law of the high concentration salt solution in the cavity,HC coupling during reconstruction of old salt rock cavern,and the operation of the old salt rock cavern are conducted.At the same time,the evaluation method of reconstructing the old salt rock cavern as gas storage is presented.The main contents and results of this thesis are as follows:?1?According to similarity principles and criteria,the appropriate physical simulation model is selected and then the test bench size and operating parameters are determined.Considering the crystallization of salt solution,the effect of injection fluid under different flow rate,temperature and concentration are studied.The results show that it is easy to precipitate the crystallization of NaCl for the brine under high temperature and high concentration when the total concentration of NaCl and Na₂SO₄ mixed solute is?318g/L.Therefore,the sum of the two concentrations should be controlled below 318g/L is helpful to reconstruct gas storage cavern when the solute concentration in NaCl and Na₂SO₄ solution is less than 318g/L.?2?In consideration of the effects of flow rate,temperature,concentration on salt crystallization,an appropriate flow rate should be selected for the old cavity transformation.On the one hand,the temperature of brine will be controlled for avoiding temperature reduce due to the temperature effect of external high flow rate fluid,resulting in brine into the supersaturated state of crystallization;on the other hand,the concentration range of the brine will be controlled at a reasonable value for ensuring the transport ability of brine in the cavity.?3?The effects of HC coupling on the distribution of flow field and concentration field are studied for the depth of 1000m in old gallery salt rock cavern by using Fluent software.From different water injection conditions of 40,60,80,97 and 120m³/h are selected.The law of interaction between concentration field and flow field in gallery salt rock cavern is obtained,including the relationship between the flow rare and the average concentrations of the top,middle and bottom of the gallery salt rock cavern is established,the concentration at the bottom?production well?:C=-0.6636Q+325,R²=0.9914,the concentration at the middle of the cavity:C=-0.8403Q+322.63,R²=0.9879,the concentration at the top of the cavity:C=-0.8017Q+298.92,R²=0.9658.It can be seen from the formula that the concentration of the cavern decreases with the increase of the flow rate.?4?In the reconstruction of the old salt rock cavern,the flow field in the cavity has the characteristics of laminar flow distribution under different water injection conditions.For the bottom of the old cavity near the wall of the salt,the only factor affecting the dissolution is time.On the one side,the bottom of the cavity will be the deposition of some insoluble,which will be a certain hindrance to the salt rock dissolution;on the other side,near the bottom wall of cavity,concentration is high and the flow rate is slow,where it is easy to crystallize.Thus,the dissolution of salt rock and reconstruction of salt storage is hindered to some extent.Therefore,in the old cavern reconstruction of the reservoir process,fully taking this phenomenon into account,the upward and lateral dissolution of the cavity should be controlled to form a more ideal cavity shape and the flow rate in the bottom of the cavity should be increased for dissolving crystallization.?5?According to the basic results of stability,tightness and economy of the gas storage cavern,a further evaluation of the available of the primary old salt rock cavern are carried out and a set of evaluation methods for the reconstruction of the gas storage cavern from old salt rock cavern are formed.The evaluation index is divided into four level indicators.This method has the characteristics of convenient and speedy.?6?Using FLAC^3D,the shape of an old gallery salt rock cavern is modeled in China.Considering the key factors such as internal pressure and creep characteristics,the stability and tightness of the surrounding rock and economy of the gas storage cavern during the operation of the old gallery salt rock cavern are simulated.The simulation indicates that the available of the reconstruction of the gas storage cavern from old salt rock cavern.