Society of Petroleum Engineers. Adapted with permission.
Core samples are small portions of a formation taken from an existing well and used for geologic analysis. The sample is analyzed to determine porosity, permeability, fluid content, geologic age, and probable productivity of oil from the site.
Drilling is the only way to be sure that oil and gas fields exist and exactly what is present in the formation. Core samples reveal the physical and chemical nature of the rock.
In this activity, you will create a model formation and “drill” for samples. When layering earth materials in cups, you should layer your cups differently to compare a variety of cores.
- 1 bag of dark sand
- 1 bag of light sand
- 1 bag of soil
- 1 bag of small gravel (aquarium size)
- 10 clear plastic straws
- 1 clear plastic cup per student (8 ounce)
- water in a spray bottle
- plastic spoons
- metric ruler
1. Use the ruler to measure. Place a 1 cm layer of one of the earth materials in the cup with a spoon. Mist with the spray bottle of water until damp, but not soaking.
2. Place another earth material 1 cm deep on top of the first layer. Moisten this layer with water until damp.
3. Continue alternating layers of earth materials and water. The total of layers together will be four centimeters deep in the cup.
4. Use a straw to extract a core sample by pushing the straw straight down through the layers of the cup.
If you hit rock, you might find it difficult to continue. Consider how drill bits are used in real drilling to churn and break rock in the sampling path.
5. Place your finger tightly over the top end of the straw and withdraw it from the cup. Observe the layers in the straw core sample.
6. Lay several core samples from different cups side by side. Compare results.
Discuss: What are core samples? What are petroleum geologists looking for when they examine core samples? How do geologists use core sampling to determine the geologic formation of rocks and sediments when exploring for oil and gas?