Why must reservoir rocks be porous and permeable?

In petroleum engineering, reservoir rocks must be both porous and permeable to effectively store and produce hydrocarbons. These two properties serve distinct but essential functions:

• Porosity: This refers to the volume of void space within the rock, such as the gaps between grains or crystals. High porosity is necessary because it determines the capacity of the reservoir to store migrating petroleum.123
• Permeability: This is the rock's capacity to transmit fluids. While porosity provides the storage space, permeability—which depends on the interconnectedness of those pores—is what allows the petroleum to flow through the rock.132

Without sufficient permeability, the oil and natural gas trapped within the pores would remain immobile and could not be efficiently extracted when the reservoir is penetrated by drill holes. Together, these properties ensure that a rock formation can act as a viable subsurface vault for hydrocarbons, allowing them to accumulate and subsequently be withdrawn for human use.34