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How do porosity and permeability affect a rock’s ability to store petroleum?

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Multiple large offshore petroleum oil rigs with cranes and equipment stand in the ocean, connected by walkways above the water. — petroleum Liquid petroleum (crude oil)—which is refined into gasoline, diesel, heating fuels, asphalt, plastics, and other useful chemical compounds—is often extracted from the ground using a series of drills and pumps.

In the context of Earth science, porosity and permeability are critical factors that determine a rock's capacity to store and transmit petroleum.1

The Role of Porosity

Porosity refers to the volume of void spaces within a rock, such as the gaps between grains or crystals. For petroleum storage, the effective porosity—the portion of void space that is interconnected—is the most significant, as it allows for the accumulation and movement of fluids. While reservoir rocks typically exhibit porosities between 5 and 30 percent, not all this space is filled with oil, as some residual water is always present.12

The Role of Permeability

Permeability is the capacity of a porous material to transmit fluids. While porosity provides the storage volume, permeability determines how easily petroleum can flow through the rock. High permeability is essential for the efficient extraction of oil from a reservoir.31

Both properties can be primary (inherent to the rock's original formation) or secondary (induced by later processes like fracturing or weathering), which can either enhance or diminish the rock's ability to hold and release petroleum.1