Analysis and control of annular pressure caused by leakage effect of completion string for HP/HT/HHS gas wells in Sichuan Basin

Abstract

Completion string leakage will result in sustained annular pressure, H2S entering the annulus and a drop in annular liquid level. Based on choke flow model, gas-liquid two phase flow model, and gas state equation, prediction model of sustained annular pressure caused by completion string leakage is firstly established. Then, buildup law, typical buildup patterns and judgment chart, and influence law of control parameters on sustained annular pressure are acquired through case study and influential factors analysis. Finally, three control measures against completion string leakage are put forward and applied in actual gas wells in Sichuan Basin. Analysis results indicate that the smaller the depth of leakage point, the greater the wellbore safety risk. Reducing the equivalent diameter of leakage point is beneficial to control sustained annular pressure. The annulus needs not to be full filled with protective fluid. Field application verifies that judgment chart and control measures have successfully realized quick judgment of wellbore safety risk and control of sustained annular pressure, ensuring production safety of actual gas wells in Sichuan Basin. The management and control methods of sustained annular pressure caused by completion string leakage validated in this work can be extended to similar marine carbonate gas fields.