Thermal Stability and Structural Characterization of Class G Oil Well Cement Paste Exposed to Elevated Temperature

Abstract

The primary objective of well cementing is zonal isolation, which needs to be met by an appropriate cementitious material that can withstand high temperature and pressures. In this paper, the thermal stability of class G oil well cement (G-OWC) paste is evaluated in terms of the change in compressive strength, volume, and microstructure after heat treatment. The results show that the thermal exposure up to 200°C did not have a significant effect on the strength and volume of the samples. The cement paste experienced substantial strength loss and shrinkage between 200 and 1,000°C. After heating up to 1,000°C, only 6.3% compressive strength was left for the sample. The drastic thermal damage is attributed primarily to the evaporation of chemical bound water and decomposition of hydration products in the cement paste as the temperature increases to 440°C. The transformation of C-S-H gel to larnite (