SUMMARY
Sustained Casing Pressure (SCP) is a critical aspect to gas well safety and environmental protection. All regulations require SCP elimination. This paper focuses on the SCP which caused by gas migration in cemented casing annulus. We modeled the gas channeling-path of cemented section and further developed a modified method to predict casing pressure rise. A field study was presented in the paper to verify the result of the prediction. We also analyzed the effects of annular permeability, initial annular pressure, gas leakage pressure and cementing isolation interval length on SCP, which suggested that, the annular equivalent permeability and initial annular pressure influence the rising rate of casing pressure without influencing the maximum; while gas leakage pressure and the length of cementing isolation interval can influence both the rising rate and the maximum, after that we discussed the prevention measures. In particular, we suggest that the rising rate and the maximum of casing pressure should be considered while determine the cementing isolation interval.