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In this study, the strength and characteristics of cement paste exposed to 200 C was examined focusing on the cement paste for SAGD (Steam Assisted gravity Drainage) well where vapor steam with about 200 C is injected to extract heavy oil. The commercial oil-well cement (OWC) and geothermal-well cement (GWC) and the GWC with fly ash were used for the cement paste. When the hardened paste was exposed to drying at 200 C, the compressive strength was slightly increased in all cement cases comparing to that with sealed curing at 20 C. It can be attributed to the increase of solid surface energy due to evaporation of adsorbed water. The compressive strength of OWC cement paste exposed to saturated steam at 200 C was greatly reduced because the pore structure became very coarse. On the other hand, the strengths of GWC and GWC with fly ash cement pastes subjected to 200 C steam were increased. The hydration products of GWC and GWC with fly ash were mainly Xonotrite and Tobermorite, respectively and leading to finer pore structure and larger strength. It is concluded that the appropriate replacement of fly ash with GWC can be effective to make pore structure dense and to improve the strength of cement paste if the moisture can be supplied to SAGD well from surrounding soil.

Study on Strength and Characteristics of Cement Paste for Well Exposed to 200 °C