Properties of Set Aluminate Cement in 600℃ Ultra-High Temperature Xerothermic Environment

The downhole environment in in-situ mining of oil shale is ultra-high temperature and xerothermic, with temperatures above 500℃, which poses a challenge to the sealing integrity of the oil well cement sheath. To deal with this challenge, the performance evolution patterns of set aluminate cement and set sand-containing aluminate cement in a long-term xerothermic environment at 600℃ were evaluated, and the microscopic structural characteristics and changes in hydration products analyzed. The results of the research show that aluminate has a certain inhibitive effect on the decline of the high-temperature strength of the set cement. After aging in a xerothermic environment at 600℃, the strength of the set cement first increases and then slowly decreases. This is because minerals with higher hardness such as corundum replace minerals with lower hardness such as gibbsite. The set cement is mainly in the form of blocky and granular structures, and the structure is still acceptable, but the sizes of the pore throats become larger and the permeability increases. The strength of the set sand-containing aluminate cement is lower than that of the set cement of pure aluminate. After dry heat curing at 600℃, the contents of quartz and corundum increase significantly. The microscopic structural evolution pattern of the set sand-containing aluminate cement is basically the same as that of the set cement of pure aluminate. The degree with which the quartz sand participates in the reaction is low. Although it can partially optimize the pore throat structure of the set cement, its cementation property becomes poorer, and the number of microfractures inside the set cement increases, leading to an increase in permeability. The research results can provide a reference for the development of aluminate cement slurries suitable for high-temperature working conditions in in-situ mining of oil shale etc.