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This teaching guide is designed to complement the 20-minute video, Crude Energy. Click here to request the video. Please note that video supplies are limited and may no longer be available. Take tons of tiny animals and plants and place them in a hot oven.
Then cover them and let them sit for millions of years. No,
it’s not the recipe for Mom’s tuna casserole. Actually, it’s a simple
explanation for how petroleum is formed. Petroleum
is made primarily of mixtures of hydrocarbons, compounds of carbon, and hydrogen.
Scientists believe petroleum hydrocarbons come from the remains of tiny animals and plants
that lived millions of years ago.
Barker
compared today’s elephants to yesterday’s dinosaurs. He said the total mass of
elephants on the earth is probably less than the total mass of ants because ants outnumber
elephants by such a large margin. When
tiny organisms die, they sink to the bottom of the sea and are mixed with mud and silt.
Over time, hundreds of feet of mud containing the organisms accumulate. Bacteria removes
most of the oxygen, nitrogen, phosphorus, and sulfur, leaving mainly hydrogen and carbon.
Lack of oxygen keeps the animals and plants from decaying completely. The
partially decomposed organisms create a slimy mass, which is then covered with layers of
sediments. Many sediments are tiny particles that come from the breakdown of larger rocks,
usually by weathering. Over millions of years, many layers of sediment pile on top of the
once-living organisms. The weight of the sediment compresses the mud into a fraction of
its original thickness. Now We're Cooking! Barker
likens the process to cooking. “If I turn the temperature of the oven up, things cook
faster. If the temperature is turned down, it cooks slower,” Barker said. Higher
temperatures usually produce lighter petroleum. Lower temperatures create a thick
material, like asphalt. As the heat continues to alter the substances, gas is often
produced. Depending on how much gas is present, sometimes it will stay mixed with the oil
and sometimes it will separate. At temperatures above 500 degrees Fahrenheit, the organic
matter is destroyed and neither oil nor gas is formed. The
mud and silt become more and more compressed and turn into a rock known as shale. As the
mud is being compressed into shale, the oil, gas and saltwater are squeezed out. The
fluids move from the original rock, known as the source rock, to a new rock, called a
reservoir rock. Porosity A
pore is a small, open space in a rock. A rock’s porosity is the ratio of
pore volume to total volume and is expressed as a percentage. The
shapes of sediments affect the porosity of a rock. Generally, sediments are not perfectly
round, but occur in many shapes. Sediment size and how closely sediments are packed also
are variables. The third factor that determines a rock’s porosity is the amount of
material that precipitated from seawater and accumulated in the pores. A porosity of 5 to
20 percent is usually considered average for sedimentary rocks. If
the pores are connected, the rock is said to be permeable. Permeability is the
ease with which a fluid can move through a porous rock. Sandstone is the most porous and
permeable of the sedimentary rocks. That’s why much of the world’s oil and gas
occurs in sandstone. Carbonate rocks such as limestone and dolomite are also good
reservoirs for oil and gas. Reservoir Rocks Oil
and gas travel through pores of the reservoir rock, with the help of water, until they
reach an impermeable layer of rock through which they cannot pass. Shales are the most
common impermeable rock. Oil Traps Another
common type of trap is the fault trap, which is formed by a fault, or fracture,
of the layers of rock. The rock on one side of the fault sometimes slips down so that a
porous reservoir rock is next to a nonporous rock formation. This creates a seal, and the
petroleum is trapped. When
parts of the reservoir rock itself are impermeable, often oil is trapped. This is known as
a stratigraphic trap. The stratigraphic trap category also includes side-by-side
changes from one type of rock to another. Now
that the oil has been cooked, moved and trapped, it will stay there until rock formation
movement causes a change in its surroundings, or until humans decide to drill a well in
that spot. Synthetic Oil Discussion Questions...
Sources Black
Gold | Recipe for Oil | Finding
Oil
Last Updated: 02/16/03 |
there
simply weren’t enough of them to create such large amounts of oil. So if the quantity
of dinosaurs wasn’t sufficient to make oil, how did tiny sea animals and plants
become oil?