What two rock types are the most common reservoir rocks?

• A. Limestone and shale
• B. Sandstone and Carbonates
• C. Sandstone and shale
• D. Dolostone and limestone

Answer: (B)

Reservoir rocks must have porosity and permeability to store and transmit hydrocarbons. The two rock types that most commonly serve as reservoirs are sandstone and carbonates. Sandstone provides well-connected pore spaces and predictable porosity and permeability, making it a classic reservoir rock. Carbonate rocks, like limestone and dolostone, often develop substantial porosity through dissolution and fracturing, creating ample pathways for fluids. Shale, in contrast, is typically low permeability and acts more as a seal or source rock, not a primary reservoir. Dolostone and limestone are both carbonates, and while carbonate reservoirs are widespread, the combination of sandstone and carbonates best captures the common reservoir rocks encountered.