Salt cavern hydrogen storage nitrogen blocking dissolution full-stage nitrogen injection volume and injection pressure prediction model and influencing factors analysis

Due to its low cost, environmental friendliness, and non-polluting nature, nitrogen is now widely used as an anti- dissolution agent in salt cavern hydrogen storage. However, there is currently a significant deviation between the calculated nitrogen injection amount and the actual value. This leads to the need for more nitrogen supplementation to stabilize the fluctuations of the gas-liquid interface, thus increasing the additional cost of nitrogen use. To address this issue, based on the physical model of nitrogen anti-dissolution, combined with gas-liquid interface control methods, solubility calculation methods, U-tube theory, and wellbore flow friction calculation equations, this paper establishes a prediction model for the nitrogen injection amount and injection pressure throughout all stages of nitrogen anti-dissolution in salt cavern hydrogen storage for both forward and reverse circulation conditions. The model is verified by comparing with the actual data of two wells in Henan region and the simulated data of two wells in a certain place. Furthermore, the impacts of the maximum and minimum air- cushion thicknesses, wellhead temperature, brine concentration, and technical casing size on the nitrogen injection amount and injection pressure are explored. The results show that: (1) Compared with existing simulation software, the model in this paper fully considers the calculation methods of nitrogen in each stage. The finally calculated nitrogen injection volume and nitrogen injection pressure are quite consistent with the actual on-site measurement data, with an accuracy rate exceeding 90%, and they are also relatively consistent with the results of the simulation software. (2) The maximum and minimum air-cushion thicknesses should be designed according to the magnitude of gas-liquid interface fluctuations. By reasonably setting the values of the maximum and minimum air-cushion thicknesses, the nitrogen usage can be effectively reduced. (3) The wellhead temperature, brine concentration, and technical casing size are all positively correlated with the nitrogen injection amount. The wellhead temperature and brine concentration are positively correlated with the nitrogen injection pressure, while the impact of the technical casing size on the nitrogen injection pressure is negligible. The research results of this paper can provide a theoretical basis for calculating the nitrogen injection amount and injection pressure throughout all stages of nitrogen anti-dissolution in salt cavern hydrogen storage, and the nitrogen injection amount and injection pressure can be adjusted according to local temperature, working conditions, brine concentration, and other related factors.