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Natural Gas: Classroom Activities

Gases Dissolved in Liquids


Goal

To understand how natural gas dissolved in oil is released.

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Background Information

Natural gas is often associated with oil wells. It can exist as a free gas which is separate from the oil or it can be dissolved in the crude oil as a dissolved gas. Gas wells do not have to contain crude oil, and they are termed "non-associated gas." In most gas wells, raw natural gas occurs by itself. Wells that contain free natural gas along with condensates of hydrocarbons are called condensate wells. The type of associations that natural gas occurs with affects the processing of the gas after extraction from the well.

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Activity Overview

Students examine the occurrence of dissolved gas within a liquid by exploring what happens when they open a can of soda. They design an experiment to measure the volume of dissolved gas.

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Materials and Equipment

Can of soda or a 20-oz plastic bottle, heat source (Bunsen burner or hot plate), 1-L Pyrex beaker (for water bath), 50 cm of rubber tubing, 500-mL beaker, modeling clay (used as a seal), goggles, plastic box (shoebox size).

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Activity

  1. Ask students to discuss the contents of a can of soda. Have them estimate the amount of gas dissolved in the soda.
  2. Have the students make connections between the can of soda and its contents, and an oil well.
    The soda in the can is in equilibrium with the confining pressure it was placed under. Likewise, oil and gas deep in the Earth rest in equilibrium, unless the pressure or temperature of their surroundings changes. The can models the reservoir and the contents represent the oil with dissolved gas.
  3. Distribute the materials to the students. Instruct them to work in groups to devise a way to measure the volume of gas that escapes from the can of soda when opened. (The can will need to be gently heated after opening).
  4. Instruct students to draw their model. Check their setup. Upon approval, students should open the soda and run the experiment.
  5. Have students complete the following:
    1. How much gas did you collect?
      Answers will vary depending on the efficiency of the design. Students have collected as much as 350 mL of gas from a single 12-oz can. Try to make sure that students collect the gas from above the surface of the soda and not in the liquid.
    2. How did your results compare to your prediction?
      Answers will vary.
    3. How would you change your experimental design?
  6. Discuss with your students the following:
    1. Describe what happens when natural gas dissolved in oil at depth rises to the surface?
      Students should recognize that the connection between the experiment and oil rising from depth is that there is a decrease in pressure on the fluid. As the confining pressure on the rising oil decreases, the volume of dissolved gas decreases to maintain equilibrium with its surroundings. The gas is released from the fluid to become a free gas.
    2. Explain the changes that happen.
      The ratio of free natural gas to oil increases unless that gas condenses and transforms to a liquid, called condensate.

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