Study on Prediction Model of Sustaind Casing Pressure in Tubing-Casing Annulus of Gas Well

At present, the problem of Sustaind Casing Pressures(SCP) in various production gas wells at home and abroad is becoming increasingly serious. Among them, the SCP in tubing-casing annulus is the most common, which seriously affects the production safety of gas wells. For the problem of the SCP in tubing-casing annulus, this paper establishes a prediction model of SCP in tubing-casing annulus of gas well by combining the leakage equation of downhole gas and the gas PVT equation of wellhead annulus, and based on the principle of pressure balance, the depth of leak point and leakage rate were studied by combining the temperature and pressure field of the gas wellbore. An example calculation was carried based on the actual data of the “A” gas well, and model was used to analyze the sensitivity of the four parameters of the SCP of tubing-casing annulus. The results show that the accuracy of the model is verified because the SCP values in tubing-casing annulus calculated by the model is in agreement with the field measured data. The equivalent diameter of the leakage point has the most significant effect on the SCP in tubing-casing annulus, and the influence of the gas-top height and the compression factor of the annulus protection fluid is second. However, they have little effect on the final stable pressure value; the depth of the leakage point has little effect on the early stage of pressure build-up, but has a greater impact on the final stable pressure value. This research results are of great significance for the diagnostic evaluation of the SCP in tubing-casing annulus and the control of the annulus pressure.