Which term describes water located in the pores of a reservoir rock, distinct from groundwater or formation water?

• A. Capillary water
• B. Intersttitial water
• C. Connate water
• D. Interstitial water

Answer: (D)

Water located in the pores of a reservoir rock is interstitial water. This term refers to the pore water that fills the spaces between the solid grains inside the rock’s pore network. It’s different from groundwater, which is water in a connected, mobile system that can flow through formations, and from formation water (connate water), which is water trapped with the rock since deposition. Interstitial water is the general pore-water present inside the rock, while capillary water is a subset of that water held in the smallest pores by capillary forces.