Suitable length of the tube-casing annular nitrogen column of gas storage well

Aiming at the tube-casing annular abnormal pressure problem of gas storage well, a mathematical model of closed annulus with nitrogen column injected has been established. Pressure variation of closed annulus under the influence of pressure and temperature has been comprehensively analyzed. Based on analyzing the annular pressure during gas injection process and gas production process of gas storage well, tube-casing annular pressure's influence law by annular nitrogen column length, temperature and pressure variation of oil tube has been studied. The result shows that the tube-casing annular pressure problem of gas storage well can be effectively relieved by injecting certain length nitrogen into annulus. The longer the nitrogen column is, the lower the tube-casing annular pressure is. When the length of nitrogen column is more than 100 meters, the change in the tube-casing annular pressure is little. The suitable length of the annular nitrogen column is 100 to 200 meters, and the suitable initial injected pressure of nitrogen is 2 MPa. Moreover, pressure and temperature variation of oil tube will influence the tube-casing annular pressure. Thereinto, temperature is the main factor. Using heat insulating material will help to reduce or avoid the annular pressure increase caused by temperature rise of oil tube during gas injection and production process.