Stress Analysis of Cement Sheath in Thermal Production Well:Effects of High Temperature Changes

In thermal recovery of heavy oil wells, stresses of cement sheath in the oil reservoir section are greater than that of conventional wells, which are due to the action of high temperature and pressure during steam injection. An analytical mechanical model is established, considering pressure and temperature loads coupling effects. The axial stress increase is more significant with the increase of temperature, compared with the radial stress and tangential stress increases, and the effect of temperature increase on the maximum shear stress of cement sheath becomes significant when temperature rise higher than 160°C. When temperature rise above 120°C, effects of temperature increase on maximum shear stress of cement sheath with different elastic modulus are differences, and reducing the elastic modulus of cement sheath is helpful to reduce the maximum shear stress in higher temperature rise. At the same time, when the temperature rise relatively small (below 160-180°C), the effect of steam injection pressure on maximum shear stress is obvious. The axial stress and the maximum shear stress of the cement sheath are increased after casing pre-tension stressed cementing, because the spring back effect of casing will lead to the production of additional axial stress of cement sheath.