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Oil: Classroom Activities

Permeability, Porosity, and Oil Source Rocks


To explore the factors that affect how easily a fluid can move through sediments and to make connections between the flow rate of oil and oil production.

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Background Information

Many people think that oil lies in big pools below Earth's surface. Actually, oil is located in the pores within rocks (called "source rocks"). When the pores are connected, oil can flow slowly through the rock. This happens when there is a difference in fluid pressure between one place in the rock and another. The flow of fluid through sediments due to this pressure difference is called the permeability of the material.

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Activity Overview

Students will explore the permeabilities of different materials. They then use their observations to determine what affects permeability and how this might relate to oil production.

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Materials and Equipment

4 fluid oz each of sediments: gravel, coarse sand, fine sand and silt/clay, four 20 oz empty identical clear plastic bottles, 4 oz measuring cup, cheesecloth and 4 rubber bands, water supply, watch with a second hand, safety scissors, paper and pen to record results

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  1. Ask students to cut one of the plastic bottles 1/3 of the way down from the top to make a funnel. Have them cover the mouth of the funnel with a double layer of cheesecloth. Ask them to secure the cheesecloth with a rubber band.
  2. Ask students to invert the funnel into the bottom of the bottle to create a funnel/container set-up. Have them repeat this with the other three bottles. Ask students to put 4 oz of each of the sediment types into a separate funnel.
  3. Tell students to have a watch ready. Instruct them to pour 4 fluid oz of water into the gravel funnel and time how long it takes all the water to pass through. Have them record this time for gravel. Ask them to repeat for the other three sediments, one at a time. Students should record their observations each time.
  4. Have students answer the following:
    1. Which sediment was the most permeable (allowed water to pass through most quickly)?
      Gravel will be the most permeable providing the sediment is well sorted.
    2. Which was the least?
    3. Can you explain why one was more permeable than another?
      Sediments with large interconnected pores are the most permeable.
  5. Ask students to consider the qualities that petroleum geologists look for in productive source rocks.
    Answers will vary. A good source will be both porous and permeable. If source rocks have consistent characteristics throughout the layer then pumping is easier to control. A good trap on the other hand should be highly impermeable.
  6. Ask students to conduct research, either in their school library or online, to find out what specific types of rocks are good source rocks and why. Have them share their findings with their class.
    Answers will vary depending on the oil field and reservoir chosen.

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