Formation Water Evaporation-Induced Salt Precipitation in Wellbore of Underground Gas Storage: A Thermo-Mechanical-Chemical Coupling Model

Summary

Formation-water evaporation-induced salt precipitation under multiphase fluid flow conditions is a common yet insufficiently understood process in saline subsurface systems. During the underground gas storage, this process will be particularly pronounced, involving complex interplays among multiphase flow, mass and heat transfer, and other physicochemical processes. How to accurately and quickly predict the salt-precipitation risk driven by water evaporation in gas storage wells is still challenging due to the complexity of salt-precipitation simulation. Given the mechanism of salt precipitation, this work presents an innovative thermo-mechanical-chemical coupling model for predicting brine evaporation-induced salt precipitation in wellbore. Meanwhile, the typical salinity-adjusted curves of saturated water vapor content in natural gas are proposed, enhancing the representation of phase equilibrium processes. The results indicate that the mass density of water vapor in the gas phase is reduced to 76% of that in a pure water system when the salt mass fraction in water-salt solutions is 0.26. At the initial stage of salt deposition, salt precipitation is more sensitive to the production schedules. Furthermore, the salt-precipitation risk of gas wells with moderate water production rates is 30% higher than that of the low or high water-producing wells. With high modeling accuracy guaranteed (98%), the new model achieves a 120-fold improvement in computational efficiency compared with the existing models, enhancing the generalization and numerical convergence significantly. This work provides a reference to design the technical operation scheme of underground gas storage for reducing the effects of wellbore salt precipitation and improving the efficiency of energy usage.