Gas injection and brine discharge in rock salt gas storage studied via numerical simulation.

Jianjun Liu,Yichen Liu,Kai Xie,Yingjie Wang

doi:10.1371/journal.pone.0207058

Abstract

Underground gas storage in rock salt is of great importance for peak-shaving and emergency gas supply. This paper addressed an actual rock salt underground gas storage facility in Jiangsu province, China, as the research project and carried out the following research centered on a detailed geological model, a salt cavern model and the process of gas injection and brine discharge. First, based on the theory of gas-liquid two-phase flow, the authors established a relationship between brine flow and natural gas bubbles under high pressure in the process of brine discharge. Second, the effect of pipe depth on the gas injection and brine discharge was simulated. The objective was mainly to choose the best combination of pipe depth and rate of brine discharge flow based on analysis of the relationship between the brine discharge pipe depth and the flow rate of the residual brine, and the optimal rate was given according to different distances. Third, the effect of residual brine on the gas injection and brine discharge was analyzed. The relationship curves between the maximum velocity on the surface of brine and the distance from the lower end of the brine discharge pipe to the bottom of the gas storage were obtained, and reasonable rates were suggested under different actual working conditions.

Highlights

There are many advantages to salt cavern underground gas storage in rock salt: for example, the creep of rock salt formations is good, the permeability of rock salt formations is low, the structure of rock salt formations is complete, the hydrogeological conditions are relatively simple, and the caprock is well separated
The purpose of the research on the effect of gas injection and brine discharge is mainly to select the best combination of pipe depth and rate of brine discharge flow, based on the analysis of the relationship between the brine discharge pipe depth and the flow rate of the residual brine
It can be seen from Fig 6(A) that if there is only a 1 meter depth of brine in the cavern, the velocity near the pipe is larger than the rate limit when the rate of brine discharge is 40 m3/h; a large number of bubbles are discharged with the brine, so the rate of the brine should be less than 20 m3/h to discharge the brine slowly out of the gas storage

Summary

Introduction

There are many advantages to salt cavern underground gas storage in rock salt: for example, the creep of rock salt formations is good, the permeability of rock salt formations is low, the structure of rock salt formations is complete, the hydrogeological conditions are relatively simple, and the caprock is well separated. The construction of salt cavern underground gas storage includes the construction of the supporting ground facilities and pipelines and drilling and completion, cavity construction, gas injection and brine discharge. The brine is discharged out of the storage after the salt rock is dissolved by clear water injected through the pipeline, and a cavity with a certain volume and shape is formed underground. It is of great significance for the construction of natural gas storage by controlling the position of pipe string and the rate of brine velocity

Research background of gas storage

Fluid dynamics theory in the process of gas injection

Numerical simulation of gas injection and brine discharge

Effect of pipe depth on the gas injection and brine discharge

The effect of the residual brine on the gas injection and brine discharge

Conclusion