Analysis of the Microstructure of a Failed Cement Sheath Subjected to Complex Temperature and Pressure Conditions

One of the main obstacles hindering the exploitation of high-temperature and high-pressure oil and gas is the sealing integrity of the cement sheath. Analyzing the microstructure of the cement sheath is therefore an important task. In this study, the microstructure of the cement sheath is determined using a CT scanner under different temperature and pressure conditions. The results suggest that the major cause of micro-cracks in the cement is the increase in the casing pressure. When the micro-cracks accumulate to a certain extent, the overall structure of the cement sheath is weakened, resulting in gas channeling, which poses a direct threat to the safe production of oil and gas. A change in the casing temperature has a limited effect on the microstructure of the cement sheath.