Model Earth Core Samples: What’s Down There?

One tool engineers use to find oil is core drilling. Huge drills extract cylinders of rock or sediment from below the Earth's surface. Petroleum engineers use microscopes to study these cores in a laboratory, looking for the presence of fossil fuels. They use their understanding of the composition of the layers of the Earth to analyze the (potential) reservoir rock properties (porosity, permeability, saturations, compressibility, etc.) to make informed decisions about where to drill, and minimize the number of costly wells they must drill to obtain oil.

After this activity, students should be able to:

• Describe the layers under the Earth's surface.
• Understand how fossil fuels are formed and where they come from.
• Understand the important role that engineers have in finding and extracting oil.

What do you know about oil and other fossil fuels? (Listen to some student ideas.) Currently, oil, coal and natural gas provides much of our nation's energy. Although, engineers and geologists are trying to find new ways of harnessing energy, the U.S. still depends greatly on oil and coal to power our cars and generate heat and light. And, oil is used to make the many kinds of plastic materials we depend on every day. These fossil fuels are combusted in large power plants that release pollutants into the air, land and water. Some of these emissions include carbon dioxide (CO₂), particulate matter (PM) and heavy metals such as lead (Pb) and mercury (Hg). Furthermore, gasoline (a product made from oil) is combusted in car motors and these emissions also enter the atmosphere (eventually settling onto water or soil or remaining in parts of the atmosphere forever). The extraction of fossil fuels is also disruptive to the natural environment, sometimes fracturing underground rock and contaminating groundwater that may be needed for drinking water. Furthermore, the gases released from drilling are potent greenhouse gases that contribute to the polluting of our planet's atmosphere—affecting the air we breathe as well as the weather and climate around the world.

Oil is only found in sedimentary rocks. Organic matter (from dead marine organisms) was deposited millions of years ago and then trapped under an impermeable layer of hard rock, or sedimentary layers. After many years, and after an increase sedimentary layers resulted in intense pressure and heat, the microorganisms trapped under these layers formed fossil fuels—of which oil is one form. When the layers of rock faulted (or folded) from tectonic plate movement or earthquakes, wells or reservoirs of oil were created (see Figure 1). Engineers tap into these reservoirs to extract oil for all sorts of purposes around the world.

Figure 1. A cut-away diagram shows large oil deposits in pockets where rocks have folded beneath the Earth.CopyrightCopyright U.S. Geologic Survey http://seeps.wr.usgs.gov

We cannot see oil under the ground, so how do we find it? How do engineers find oil? (Listen to student ideas.) One method used to find oil is core drilling, in which long cylinders of rock or sediment, called cores, are removed from deep below the Earth's surface. Once these cores are brought up to the surface, they are analyzed by engineers and geologists to find the presence of oil. Clearly, the Earth's surface cannot be poked with holes until drillers get lucky and hit oil; so instead, geologists and engineers use their knowledge about the Earth's layers to determine the best, most logical place to drill for oil. Can you name the layers of the Earth? (Answer: Inner core, outer core, mantle, crust.)

In this activity, we will take core samples from a model of the Earth and look for oil, as represented by black or brown clay. Some of you will strike oil and some may not!

Before the Activity

• Gather materials and make copies of the Core Sample Worksheet (PDF), one per student.
• Prepare a layered model of the Earth for each student group. Either have the teacher or aides make them in advance, or have the groups each make a model Earth and put them all into a grocery bag and randomly pass them back out to the teams. Steps to make the Earth models (refer to Figures 2 and 3):
• • Take equal, quarter-size balls of each clay color of the clay.
  • Flatten each color to represent a single layer of the Earth.
  • Stack three of the layers on top of each other.
  • For half of the samples insert an "oil" layer (of black or brown clay) somewhere between the layers. (Note: Make sure all samples are the same height.)
  • Cap all the samples with light brown clay on top and dark blue clay on the sides (to hide the interior colors) to make the globe.

Figure 2. An example layers of the Earth model with the top cap layer, but without clay around the outside.CopyrightCopyright 2004 Jessica Todd, ITL Program, College of Engineering and Applied Science, University of Colorado Boulder

With the Students

1. Conduct the pre-activity assessment and present the Introduction/Motivation content to the class.
2. Divide the class into groups of three students each.
3. If prepared in advance, hand out a clay Earth model to each group. If not prepared in advance, guide the teams to each prepare a clay model as described in the Before the Activity section. Put all the models in a grocery bag and randomly hand them back to each team.
4. Tell the students to imagine that this small model represents the big oil fields of the world such as in Texas or the Middle East.
5. As a class, review the layers of the Earth by sketching and labeling the layers of the clay model on the classroom board: inner core, outer core, mantle, crust (see Figure 3).

Figure 3. A simple diagram of the layers of the Earth.CopyrightCopyright http://volcano.und.nodak.edu/vwdocs/vwlessons/lessons/Earths_layers/Earths_layers3.html

4. Have students fill out worksheet Part A.
5. Next have each group take its three straws (each student manipulates one straw) and plunge them into the model Earth. Next, they carefully remove the straws to reveal three core samples.
6. Have students use scissors to carefully cut open the plastic straw. Have them use caution when cutting near the clay plug, so as to not smash the clay layers.
7. Remove the clay plug.
8. Instruct students to fill out worksheet Part B.
9. As a class, go over the worksheet.
10. Assign students to individually write a short journal entry from the point of view of an engineer who has just discovered the layers of the Earth at one location through core sampling. Ask students to include their questions, concerns, feelings and any other thoughts about the experience.

Pre-Activity Assessment

Brainstorming: Ask a question and solicit student answers. Remind students that in brainstorming, no idea or suggestion is "silly." All ideas should be respectfully heard. Encourage wild ideas and discourage criticism of ideas. At this point, do not provide the "right answer." Just tell students that they will find out during the activity. Ask:

• How do engineers find oil? Any ideas?

Activity Embedded Assessment

Predictions: Have students predict whether or not they expect to strike oil while taking core samples, recording their predictions on the Core Sample Worksheet (PDF). Later, when going over the worksheets with the class, revisit their predictions.

Worksheet/Pairs Check: Have students work individually on the Core Sample Worksheet (PDF). Then direct students to exchange their worksheets with another group member to check and compare answers.

Post-Activity Assessment

Journaling: To conclude, assign students to individually write a short journal entry from the point of view of an engineer who has just discovered the layers of the Earth at one location through core sampling. Ask students to include their questions, concerns, feelings and any other thoughts about the experience. Review their journal paragraphs to gauge their depth of comprehension.

What should happen: Students obtain a nice core sample with clearly defined layers contained in the straw.

Oops, it did not happen. Why?

• If the layers mixed or smashed together, the clay is too soft. Let the clay dry for a short time after creating the model Earths. But do not let the clay become too dry or the straws will be unable to cut through it. 
• After cutting the straw, the core sample got smashed. ­Since this is a delicate process, it may help to have an adult try it again using a razor blade.

Simulate the creation of fossil fuels in a soda bottle. See details about this the coal formation lesson at http://teachcoal.org/lesson-plan-coal-formation. Simplified instructions:

• Remove the label from a 2-liter plastic soda bottle.
• Add a 2-inch layer of sand or silt on the bottom.
• Add about 4 inches of water.
• Let the sand settle and then add some twigs, leaves and other organic matter on top.
• After two weeks, add a second 2-inch layer of silt or sand to the top.
• Wait another two weeks and then pour out any remaining water.
• Wait another week and observe the fossil fuel you have made.

ACF Lesson Plan: Coal Formation, grade level K-6. American Coal Foundation. Accessed 2004. (Students conduct a simulation of the formation of coal and practice the lab skills of hypothesizing, observing and explaining their findings.) Originally found at http://teachcoal.org/lesson-plan-coal-formation

Educational resources for students and teachers. Office of Fossil Energy, U.S. Department of Energy. Accessed 2004. Originally found at http://www.fe.doe.gov/education/