With the deepening of oil & gas reservoirs exploration and development, an increasing number of sour-gas reservoirs especially those with high content of H2S are developed in the world. Phase transition of high-sulfur gas or H2S will be easy to occur near the wellhead, and bottom-hole pressure reduces drastically, which possibly leads to serious blowout. Considering the special physical properties of high-sulfur gas and its possible phase transition in the wellbore, a mathematical model for wellbore flow and heat transfer during formation high sulfur gas invasion was established. The heat transfer and pressure were coupling calculated along with high-sulfur gas physical properties parameters, and a solution method of the model was proposed. The wellbore pressure and properties of gases with different content of H2S rising process along the wellbore were analyzed. The reason of high-sulfur gas easy to result in the problem of well control was presented. The paper exhibited the results of the bottom-hole pressure and depth of phase transition varying with different influx rate, injection rate, choke pressure and land surface temperature, and the reasons of wellbore pressure and phase transition influenced by these operating parameters were discussed respectively. The study is of certain significance for improving the safety of acidic oil & gas reservoirs exploration and development.

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