Modeling Multiphase Transport and Sulfur Deposition of Wellbores With Application to Sour Gas Production

Summary During the annual pressure decline from high sulfur gas reservoirs, sulfur deposition in the wellbore significantly limits the increase in natural gas production. A comprehensive understanding of multiphase transport and sulfur deposition within the wellbore is essential for enhancing gas production. A two-phase flow model based on pairwise force smoothed particle hydrodynamics (PF-SPH) is developed to meter-scale capture gas-water flow behaviors. In contrast to the conventional modeling methods, this model accounts for fluid flow modes, interphase slip velocity, and well wall friction. The model is then integrated into a kilometer-scale, three-phase flow mathematical framework to predict sulfur deposition distribution and other critical parameters such as liquid holdup and gas production. This method incorporates the dynamic changes in the effective transport cross-sectional area of the wellbore induced by sulfur deposition and establishes a sulfur transport model with thermodynamic phase transition. After validating the established model with experimental well data, this work tests the reliability of predicting sulfur deposition location under the influence of the sulfur particle nucleation mechanism. The results indicate that the sulfur deposition morphology exhibits a hump shape throughout the entire wellbore, with the maximum thickness shifting downward over time. Even the depth corresponding to the maximum sulfur deposition thickness in the wellbore will exceed 1000 m after 2021. When the unilateral maximum sulfur deposition thickness along the 3.5-in. tubing diameter exceeds 0.01 m, implementing desulfurization measures is most effective in increasing natural gas production. Due to the high cost and long time of mechanical sulfur removal, there is an urgent need to develop efficient sulfur solubilizers suitable for wells deeper than 1000 m. Besides, this work can dynamically predict the situation of water production wells and has been successfully applied to two water-bearing wells. It is enlightened to continuously monitor the longitudinal distribution of liquid holdup and take timely drainage measures to prolong the stable production of gas wells.