Carbon Dioxide and the Environment
Porosity and Permeability
Some sedimentary rocks are porous, like a sponge. Tiny particles of sand
are held together with rock ‘cement.” Pressure, time and sediments create this
natural type of “cement.”. Over time, many layers of sand and sediments are
compacted into sedimentary rock. Tiny spaces, or pores, exist between the
particles that allow the rock to hold a liquid. Many pores may be connected to
form a pore passage. Rocks that contain pores and pore passages are
identified as porous and permeable. Permeability is the ability of liquids and
gases to move through pore spaces in rocks. A rock may be porous and
permeable. A rock may be porous, but if the pore spaces are not connected
together, the liquids will not be able to pass through the rocks.
Trying to “see” what is beneath the surface of the Earth is one of the jobs
of a geologist. Rather than digging up vast tracts of land to expose what’s
underneath, core samples can be taken and analyzed to determine the likely
composition of the Earth’s interior. The geologist cannot go down into the
well to see the rock since the hole is only about 20” in diameter at the surface.
But, the geologist can ask for a core sample. Core samples can be studied to
see how much liquid is in the pores of the rock. This is a study of the rock’s
porosity. Measuring the porosity of rocks would allow a geologist to see
whether the area would be good for Carbon storage. If a rock is really
porous, then it would be a good reservoir. If the rocks were not porous, it
would be a good capstone. Since Carbon Dioxide would be stored in the pores
of the rock as a liquid, these measures would be important.
Let’s experiment with porosity of rock. Keep in mind that a good
“reservoir” for CO2 sequestration would have both high porosity and high
permeability. A “capstone” would have low permeability and low porosity.
Part I.
Materials:
3 different sedimentary rocks Magnifying glass
(sandstone, shale, mudstone,
siltstone, conglomerate etc)
Procedure:
1. Observe each sample of rock with the magnifying glass. Record
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observations like grain size, colors, spaces, etc..
Observations:
Sample 1
Sample 2
Sample 3
Part II.
Materials:
1 bag of large gravel
3-600 ml beakers
1 bag of sand
1 bag of small gravel
Water colored with food coloring
1-100 ml graduated cylinder
Procedure:
1. Fill one beaker to the 350 ml mark with large gravel. Fill another beaker to
the 350 ml mark with small gravel. Fill a third beaker with 350 ml of sand.
2. Fill the graduated cylinder with 100 ml of water.
3. Slowly pour water in the first beaker until it reaches the top of the gravel.
Record exactly how much water was poured into the beaker. (If you need
more than 100 ml of water, fill the graduated cylinder again.
4. Follow step three for the other two beakers. 5. Calculate the porosity of
the three materials using this formula:
Porosity= volume of water ÷ volume of material
x 100
Carbon Dioxide and the Environment
Porosity and Permeability
Data: Porosity
Type of Material
Volume (ml) of
water poured
Volume (ml) of
material
% pore space in
material
Large Gravel
Small Gravel
Sand
Pore Space =Volume (ml) water poured into bottle ÷ Volume (ml) of substances
in bottle X 100
1. What did you discover?_______________________________________.
2. What do you think would happen if you put gravel and sand together? Test
and find out:
_____________________________________________________________________________
___________________________________________.
Part III:
Determining how pores space affects permeability.
Prediction: I think the ____________sediment will have the most permeability,
because ___________________________________________________.
Materials
4 plastic cups with holes
punched in the center
Stop watch
Coffee filters for each
cup
2 beakers
4 types of sediment
(sand, rock, clay, soil)
Permanent marker
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Procedure:
1. Place a coffee filter into each cup.
2. Label each cup with a sediment type.—one will be a sand cup, another will
be a rock cup, another will be a clay cup, and the last will be a soil cup.
3. Put 100 mL of sand, rock, clay and soil in the appropriate cups.
4. Place the sand cup in an empty beaker, so you can measure the amount of
water
filtering through the sediment type.
4. Be ready to start timing flow soon.
5. Slowly pour water from a beaker or other water container into the plastic
cup
with one of the sediment types. Do one test at a time.
4. Keep the water level slightly above the top of the substrate in the plastic
cup. 5. TART TIMING THE FLOW when the water starts to come out of the
plastic cup and into the beaker.
6. STOP TIMING THE FLOW␣when the water level reaches 100 mL.
7. Share your data with 3 other groups to fill in Trial 2 and Trial 3.
8. Average the times and complete the calculations using the average time
(mean).
Data: Time in Minutes
TYPE OF
SEDIMENT
Sand
Rock
Clay
Soil
Trial 1
Trial 2
Trial 3
Average
Time (mean)
Calculations: Permeability = volume of water (mL) divided by time in minutes.
Sand: 100mL ÷ _______________min. = ______________mL/min.
Rock: 100mL ÷ _______________min. = ______________mL/min.
Clay: 100mL ÷ _______________min. = ______________mL/min.
Soil: 100mL ÷ _______________min. = ______________mL/min.
Carbon Dioxide and the Environment
Porosity and Permeability
Sand: Rock: Clay: Soil:
Conclusions: (look over your data and your background information)
1. Which sediment (sand, rock, clay or soil) had the greatest
permeability (most permeable)?____________________________.
2. Which sediment (sand, rock, clay or soil) had the least
permeability (least
permeable)?______________________________________.
3. Was your prediction correct?
Why or Why not?
___________________________________________________________________
______________________________________.
4. Based on what you have learned, which type of sediment would be
better for a reservoir for geological carbon
sequestration?_______________.
5. Color the pore space for each type of sediment.
6. Which has more porosity?________.
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7. Which has more permeability?______.
8. Which would make a better reservoir for CO2
sequestration?_____?
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