TESTING CAUSE AND EFFECT
lecture introduced correlation as a means for inferring
cause and effect relationships. The purpose
of today's lecture
is to show how correlation can also be used as a
means to test
cause and effect hypotheses.
geologic example used to illustrate how correlation can be
used as a means to test cause and effect
hypotheses is known
slow, downward movement of the land
surface. There are
various causes of this phenomenon,
are considering only one specific type (called
by the authors of your text), which can occur
fluids (water, gas, and/or oil) are removed from
the geologic conditions allow groundwater to occur
permeable materials that are sandwiched between
by lowly permeable
materials. This is called
Notice that confined groundwater occurs under
which can result in flowing
OIL AND GAS RESERVOIRS
Oil and natural gas are fluids produced deep within the earth as
matter is subjected to heat and pressure. Oil and
gas rise towards
the land surface until they are
trapped by lowly
formations. These fluids occur under pressure and
are thus analogous
to confined groundwater.
WHERE SUBSIDENCE OCCURS
Deep subsidence occurs in
various locations across the
What do these locations have in common?
These are locations where fluids are pumped
from layers of
sandy sediment within the subsurface.
fluids are under pressure: both
and pressurized oil and gas
This is the world's largest area of subsidence
and is an area
where groundwater is pumped from confined
b. Long Beach, California:
This is an area where as much as 30 feet of
an oil and gas field.
When fluids under pressure
within the subsurface are removed, the
drops. If the formation from which fluids are taken is
compressible sediments, a reduction in fluid pressure
can cause the
formations to slowly subside.
the hypothesis that removal of pressurized fluids causes
subsidence, pumping and subsidence data can be plotted
Santa Clara Valley, California
This hypothesis can also be tested by applying the model in an
to solve subsidence problems.
Example: subsidence in the Long Beach, California area has
been arrested by using injection wells to
water back into the oil and gas reservoir.
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