WHERE IS OIL FOUND?
Brian J. O'Neill
Shell Offshore Inc.
P.O. Box 61933
New Orleans, LA 70161
Level: Grades 2 - 6
Estimated Time Required: 30 minutes
Anticipated Learning Outcomes
Students will learn that crude oil is found in porous rocks
(reservoirs) rather than in caves or caverns.
A common misunderstanding of the oil business is what a
"reservoir" is. The term "pool of oil" conjures up images
of underground caves filled with oil. In fact oil and natural gas are found
in the pore spaces surrounding grains comprising sedimentary rocks. In this
demonstration students will see what porosity is by observing the filling
of pore space by a liquid.
Fill bottle with water and add several drops of food coloring
to tint the water (I use blue food coloring to tint the water dark blue
to simulate crude oil). Fill one jar completely with marbles. Keep bottle
of colored water hidden until ready to use.
Oil was formed from layers of sediments rich in the remains
of tiny (microscopic) plants and animals. As the layers were buried deeper
and deeper below younger layers of sediment, the plant and animal remains
were heated and squeezed, and altered into crude oil. This "high pressure
cooking" expelled the oil from the "source rocks", the layers
in which the microscopic plants and animals originally were deposited.
Oil floats on water because is is lighter (less dense). The newly formed oil migrates through pores and cracks in surrounding rocks upward toward the surface. The oil will float on the groundwater within porous layers of rock.
The crude oil continues to migrate until it reaches the surface at an "oil seep" (a famous example is La Brea Tar Pits in California). Many times, though, the oil is trapped underground by impermeable layers (such as shales), in which the pores are too fine to allow the crude oil to flow through. It is this trapped oil that explorers seek. Oil wells are drilled into these traps and the oil can then be brought to the surface and transported to an oil refinery for processing. Gasoline and motor oil come from refining crude oil.
This activity was inspired by discussions with Linda E. Okland about an ARCO Alaska speakers' kit which included a similar demonstration.
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