A hydrocarbon well downhole fluid acquisition and injection system for selecting and stimulating zones based on operations of the system. Target depths in a hydrocarbon well are identified, and reservoir fluids may be acquired or tagging agents may be injected at the target depths using a specialized hydrocarbon well downhole fluid acquisition and injection system. The well may be operated to generate flow of fluids, and the reservoir fluids may be monitored and assessed for the presence of tagging agents. The presence of tagging agents and the fluid sample may be assessed to identify zones that may be candidates for stimulation or other operations.