Modeling multiphase fluid flow and salt precipitation due to water vaporization in producing wells of underground gas storage

Abstract

During the production period of underground gas storage (UGS) with high-salinity formation water, salt precipitations are formed due to sharp drop of the pressure and temperature during the gas flow along the wellbore. Based on the mechanism that formation water is evaporated into gas phase and the remaining water becomes supersaturated and salt precipitates, this paper innovatively established a wellbore multiphase flow model using K-value to characterize the gas–water phase state and formation water evaporation. The developed model also incorporates energy conservation equations to consider the thermal state of gas flow, and includes the calculation of heat loss to surrounding formations when the multiple-phase fluids (gas, water, oil) flow through the tubing or annulus. The PDE equations are numerically solved by the fully-implicit finite volume method. Sensitivity analysis is further conducted to investigate the effect of gas production rates, water–gas-ratio (WGR), bottom-hole pressure (BHP), tubing diameter and formation water salinity on salt formation along the wellbore based on the proposed model. The model developed in this study is good at estimating salt precipitation location along the wellbore and its timescale. This work can provide valuable guidance to salt mitigation strategies and managements of gas well production in the UGS.