Study on the whole life cycle integrity of cement interface in heavy oil thermal recovery well under circulating high temperature condition

Cement seal failure is common in heavy oil thermal recovery wells, but the effects of steam stimulation on wellbore interface seal performance is unclear. The finite element model of plastic zone formation of cement sheath during high temperature circulating is established. The damage variable of the cement sheath is proposed to define the elastic-plastic transformation process of cementing interface, the interfacial debonding and micro-annulus size caused by thermal stress cycling are quantified, and the effects of key parameters such as steam injection temperature, cycle times, mechanical properties of cement sheath on the change of interface integrity are clarified. The results show that the tensile failure of cement sheath and the micro-annulus always formed on the inner wall of cement sheath, and outer wall remains intact. Excessive steam injection temperature (360 °C–420 °C) will cause an 8–45 μm micro-annual, excessive elastic modulus of cement sheath (>10 GPa) will cause a 20–62 μm micro-annular, the cement sheath with heat shrinkage property will form a 47–54 μm micro-annulus. Based on the sensitivity analysis, the matching relationship between the thermal cycle construction parameters and the performance index of cement sheath is established. The results can provide a reference for the design of cement parameters and engineering parameters under the thermal stress cycles.