Sealed annulus thermal expansion pressure mechanical calculation method and application among multiple packers in HPHT gas wells

For high-pressure and high-temperature (HPHT) gas wells with high production rate, the annulus expansion pressure caused by the change in annulus temperature and pressure creates large effect on the mechanical behavior and safety of strings among multiple packers. Based on the laws of the conservation of momentum and energy and the transient heat transfer property between the wellbore fluid and the annulus fluid, a calculation model of the temperature and pressure fields on single-layer and multi-layer annuli was established. For the completion strings with multiple packers, the calculation model of the sealed annulus thermal expansion pressure among multiple packers was established with an overall consideration of the effect of sealed annulus temperature and the effect of volume changing. An example of a HPHT gas well in Sichuan province of China was analyzed, The results show that the thermal expansion pressure of the tubing-production casing annulus is minimized and the thermal expansion pressure of the intermediate-surface casing annulus is maximized; The relationship between the sealed annulus thermal expansion pressure and the temperature difference is linear; Pressure increment caused by the temperature effect plays the leading role, and the construction rate of the volume changing effect for the sealed annulus thermal expansion pressure increases along with the increase in temperature; Based on the safety evaluation, the maximum production of the sample well is 286 × 104 m3/d, when the production is 175 × 104 m3/d, the maximum setting space between dual packers is 258 m. Releasing pressure of each annulus in the process of production and testing can reduce the annulus thermal expansion pressure, the analysis of the sealed annulus thermal expansion effect among multiple packers is of great significance to evaluate the safety of strings, optimize the completion plan and establish a reasonable production system.