What term describes forcing substances into a porous and permeable subsurface rock formation under vacuum?

• A. Extraction
• B. Sequestration
• C. Injection
• D. Infiltration

Answer: (C)

Forcing a fluid into a porous, permeable subsurface rock formation is called injection. This term captures the act of introducing a substance into a reservoir through a well, typically under pressure to move the material into the rock’s pore spaces. It differs from extraction, which is about removing fluids from the formation, and from infiltration, which is the natural, passive movement of water from the surface into soil or rock rather than a deliberate push into a deep formation. Sequestration involves underground storage of substances, but the focus there is on storage as the goal, not the act of forcing the material into the rock.