Comparison of Nitrogen Gas and Thermal-Insulation Liquid to Control the Temperature–Pressure Effect in Deep Gas Well

Thermal-insulated liquid and nitrogen gas are two common methods to control the trapped annular pressure caused by the temperature–pressure effect, but few researches analyzed the control performance of these two measures applied in the deep gas well. Therefore, this paper builds a model to compare the control performance and a safety factor is proposed to evaluate the control performance when the tubing is totally blocked. The results indicate that the tubing-casing annulus temperature difference creates the conditions for the trapped annular pressure. Only when the production rate exceeds a certain value, can the thermal-insulated liquid reduce the trapped annular pressure. The nitrogen gas can achieve good control performance after the nitrogen gas volume exceeds 0.03 regardless of the production time and the production rate. To avoid the tubing collapse risk, the annular pressure should be controlled under the critical value. However, the thermal-insulated liquid is not able to reduce the annular pressure to the critical value. The nitrogen gas can prevent tubing collapse under different liquid densities by suitable volume. Therefore, the nitrogen gas is recommend.