In this brief review, a comprehensive collection of previous studies about geochemistry in geologic CO₂ utilization and storage is presented and discussed to demonstrate the importance of CO₂-rock and CO₂-wellbore cement interactions in geologic CO₂ utilization and storage scenarios. For CO₂-rock interaction, CO₂ injection reduces the pH of brine in CO₂ storage reservoir, which triggers dissolution of silicate and oxide minerals in the reservoir. Dissolution of silicate and oxide minerals causes concentration increase of cations and anions, which induces secondary precipitation of silica, silicates and carbonates. For CO₂-cement interaction, the interaction between CO₂ and wellbore cement results in formation of a unique "sandwich" structure in cement (i.e., one carbonate precipitation zone in the middle and two dissolution zones on two sides). For both CO₂-rock and CO₂-cement interactions, pH plays a key role in the extent of mineral dissolution and precipitation, and the extent is dependent on pH buffering capacity of the CO₂ storage reservoir. The potential of CO₂-induced contaminant mobilization in deep CO₂ storage reservoir and shallow aquifer is also discussed, and the chance for CO₂ injection and CO₂ leakage to cause severe shallow aquifer contamination is low.