Abstract: The marine gas pool in Yuanba is featured by great burial depth, high temperature, high pressure, high content of H2S and medium content of CO2, etc. The presence of H2S and CO2 in gas wells deteriorates the annular corrosion environment. In view of the special annular corrosion environment in high sulfur content gas wells, an organic acid salt protective fluid with controllable density of 1.59 g/cm3 and temperature resistance of 160 ℃was generated by adding imidazoline H2S and CO2 inhibitors, ferrous stability, deoxidizing bactericide, cleanup additive and pH modifier. The indoor experiment shows that organic acid salt annulus protection fluid is very stable in resisting high temperature and corrosion rate is far below the designed value of 0.076 mm/a and bactericidal ability is up to 99%. The protective fluid was applied to three ultra-deep wells of marine gas pool in Yuanba, and the effectiveness was favorable. Among the wells, the Well Yuanba 204-1H had a cumulative gas production of 133.92×104 m/d by acid fracturing test; during gas testing, the tubing and casing in the annulus had no leaks, so the annulus protection fluid functions very well to prevent corrosion of tubing external wall and casing internal wall and hence ensures safe and long-term service of tubing and casing.