Effect of cement thickness and its mechanical parameters on cement stress

Whether cement thickness is reasonable or not is related to cementing efficiency and cementing quality, simultaneously，the late cement mechanical reliability will influence long-term zonal effective isolation. So it is necessary to find out the influence law of cement thickness and its mechanical parameters to cement stress, analyze the thickness sensitivity of cement and optimize cement mechanical parameters. For this purpose, an analysis and study of cement stress state has been carried out based on elastic theory. The results show that circumferential stress at innner surface is maximum, therefore, is cement’s dangerous stress. Maximum circumferential stress decreases with the increase of cement thickness, but its gradient is larger when cement thickness is less than 25.4 mm, as cement thickness increases, the maximum circumferential stress gradient decreases gradually until hardly changes. For cement of a certain thickness, the greater the elastic modulus, the greater the circumferential stress; the greater the poisson ratio, the smaller the circumferential stress. This study result can be used to guide optimization of cement thickness and cement slurry formulations.