Development and design of new casing to mitigate trapped annular pressure caused by thermal expansion in oil and gas wells

Trapped annular pressure is caused by liquid thermal expansion in oil and gas wells. A casing is developed to mitigate trapped annular pressure with low cost and overcome the limitation of well structure and location. This casing consists of coupling, relief valve, inner wall, relief space and outer wall. It can increase annular volume change rate by using relief valve to connect trapped annulus and casing relief space. Higher annular volume change rate can reduce or even eliminate trapped annular pressure. To prove the feasibility and optimize parameters of mitigation casing, models are built to calculate trapped annular pressure and annular temperature change of multiple annuli. The analysis indicates mitigation casing can effectively and permanently reduce trapped annular pressure. The extreme annular pressure change and pressure in case well are as high as 120.02 °C and 139.74 MPa, but annular pressure no longer exists when 36 mitigation casings are installed. Optimal number of mitigation casing is determined by annular temperature change and mitigation objective. Suitable design can reduce the number of mitigation casing while maintain strong mitigation effect. Mitigation casing number of case well is reduced 27.27% after optimization.