Cavities Left After Oil Extraction
Country: United States
Date: Summer 2009
What happens to Earth when oil is extracted? What is in
place after the oil is gone? Is it an air pocket, and could it
collapse into itself?
Good question John.
We need to remind ourselves that oil fields are not big caves in the
ground despite how diagrams show them. Oil and gas are tucked into
the spaces between the rock particles known as the porosity. An oil
field is more like a block of porous Styrofoam full of oil than it
is a big bag of oil.
In most cases, the rock grains are touching and the rock supports
itself even without the oil in it (like dry sandstone you find in
buildings and walls). So when oil is removed there is no
change. In most cases, water flows from the surrounding rock into
the spaces left behind by the oil.
You go from an oily block of rock (Styrofoam) to a watery one.
If you want more information try the web with keywords such as oil
and gas reservoirs, oil migration, or oil secondary recovery or
e-mail me at the address below.
I hope that helps.
R. W. "Bob" Avakian
B.S. Earth Sciences; M.S. Geophysics
Oklahoma State Univ. Inst. of Technology
The crude oil and natural gas occupy very small (microscopic)
spaces in the rock. Oil and gas are under pressure so that when a
drill bit penetrates the rock, the oil and/or gas gush out the well
pipe to the surface. At some point the pressure decreases and the
oil/gas no longer gushes. Then the drillers inject some material such
as water of carbon dioxide under pressure to push out more gas/oil.
when this treatment fails to produce more product, the drillers can pump
oil detergents to break the surface tension between the rock and oil
molecules and then add more water or carbon dioxide.
At this point a fair amount of oil/gas remains -- up to 30 - 40%.
The oil/.gas will stay there until a new method of extraction is developed.
The rock formations that held the gas/oil remain in place, sitting on the
rocks below and holding up the rocks above.
Click here to return to the Environmental and Earth Science Archives
Update: June 2012