Earth Science Week Classroom Activities

Properties of Fluids in Reservoirs

American Association of PetroleumGeologists

Activity Source:

American Association of Petroleum Geologists.
Adapted with permission from EarthComm , American Geosciences Institute.

Petroleum geologists play a vital role in locating energy resources. They use a variety of methods to collect the data they need to find reservoirs of oil and natural gas.

When they find these reservoirs, petroleum geologists need to calculate their volume. They also need to estimate how much they can recover (remove) from the reservoir. This helps them to determine the possible value of the discovery.

By using a model, this investigation will help you to understand the physical relationships between natural gas, oil, and water in a reservoir and how these relationships can affect recovery.


  • 500 mL clear plastic soda bottle with cap
  • Supply of vegetable oil
  • Water
  • Protractor
  • Notebook and pen


  1. Pour water into the soda bottle until the bottle is about half full. Add vegetable oil until the bottle is three-fourths full. Screw the cap tightly onto the bottle. The water, vegetable oil, and air in the model represent water, crude oil, and natural gas. The bottle itself represents an oil and gas reservoir.
  2. Slowly turn the bottle upside down (if you shake the bottle or turn it quickly, you will make bubbles in the oil, which will interfere with your observations). In your notebook, sketch a diagram to represent the relationship between the oil, water, and air. Why do you think that the material stacks in the order that it does?
  3. If a well is drilled into an oil and natural gas reservoir, what material would it encounter first? Second? Third? Record your ideas in your notebook.
  4. Tilt the bottle at a 45-degree angle and hold it there. Repeat this with a 10-degree angle. Look at the bottle from the side, and then from the top. Draw a diagram of the side view of the bottle when it is tilted at a 45-degree angle versus a 10-degree angle.
  5. How does the surface area covered by the oil change with the angle of the oil reservoir (bottle)? Imagine drilling a vertical well through the bottle. This represents a well being drilled into reservoirs that are sloping at different angles in the subsurface. Would the well penetrate a greater thickness of oil when the reservoir is at a 10-degree angle or when the reservoir is at a 45-degree angle? Why?