Storing CO2 underground by geological reservoirs is one of the ways to reduce atmospheric greenhouse gases. In the dry situation

CO2 has not harmed. But

when doing the geological reservoirs

the situation was often on the aquifers or deep saline aquifers. CO2 combined with water will become the carbonic acid (H2CO3) that makes cement alkalinity and compressive lower. This paper attempts to study the mechanical properties

chemical compositions

and microscopic structures of API G cements with different additives in the saturated-CO2 condition (atmospheric pressure

70 ℃). The additives under investigation include fly ash

bentonite

and barite with silicate that try to find better well cements in CO2 operation wells. The evolution of the mechanical properties including compressive strength and microscopic structure analysis including XRD

EDS

and SEM

were recorded over a period of 28 days. The carbonized depths of the samples over time were also observed. This study finds that the API G cement with fly ash displays the best compressive strength with deepest penetrating depth of carbonization. The API G cement with bentonite with higher water content has the lowest compressive strength with shallowest penetrating depth of carbonization.