# Rocks As Reservoirs: Porosity and Permeability

GEO210B Spring 2007

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GEOL 103
LAB 18 – Rocks As Reservoirs

Lab 18 (At-Home): Due at 5pm on Friday November 18ht
Rocks As Reservoirs
Gregory Baker (Aug 2016)
Lab 18 Part A:Porosity & Permeability
Question A.1: Define porosity IN YOUR OWN WORDS. Note: You will not receive credit for either copying the definition directly from the video or from definitions available on the internet. Your answer does not need to “sound” scientific—use your own words.

· Porosity is also referred to as void fraction in geography; it is the measure of rock to hold fluids. It is usually expressed mathematically as open spaces available in rocks divided by total space of the rock.

Question A.2:Do rocks made up of large grains (pebbles) have the ability to hold much more water than rocks made up of smaller (sand) grains? In other words, do course-grained rocks always hold much more water then finer-grained rocks? Explain.
· Coarse-grained rocks have the ability to hold more water than rocks made up of smaller grains because they have a higher porosity, coarse-grained rocks cannot be tightly packed together leaving many open spaces.
Question A.3:Define permeability IN YOUR OWN WORDS. Note: You will not receive credit for either copying the definition directly from the video or from definitions available on the internet. Your answer does not need to “sound” scientific—use your own words.
· Permeability is the ability of a rocklayer to allow fluids pass through. It is usually expressed as high or low depending on the pressure applied on the rock for fluid to squeeze through.

Question A.4: Using what you now know, give at least one example of a rock type that could be characterized by each of the following–
a) Low porosity, low permeability
· Tight gas
b) High porosity, low permeability
· Shale
c) Low porosity, high permeability
· Quartz
d) High porosity, high permeability
· Gravel
Lab 18 Part B: Aquifers

Question B.1: Define aquifer IN YOUR OWN WORDS. Note: You will not receive credit for either copying the definition directly from the video or from definitions available on the internet. Your answer does not need to “sound” scientific—use your own words.

· Aquifer is a layer of rocks with high porosity and high permeability that holds underground water.
Question B.2: What kind of aquifer is typical for Kansas? Give details.
· The Ogallala aquifer is typical for Kansas. The aquifer is high plained and provides for 70% of water needs in Kansas. The aquifer is composed mainly of sand, silt, clayrock and gravel and varies from place to place. Porosity and permeability of the aquifer also vary from location to location.
Question B.3:What are the three different types of materials—rock types—that make up the common aquifers in the United States? Explain the properties of each type of rock aquifer. Note: You will not receive credit for either copying the definition directly from the video or from definitions available on the internet. Your answer does not need to “sound” scientific—use your own words.

· Sandstones, gravel, and clayrock debris make up most of the aquifers in the United States. The high level of quartz in sandstone makes it highly permeable, and it retains its high porosity. Gravel has high porosity and high permeability, the properties of gravel in USA aquifers are almost similar with those of sandstone. Clayrock has the highest porosity among the three rocks, and it’s also the most permeable. Rocks that comprise aquifers must possess high permeability and high porosity.

Lab 18 Part C: The Ogallala Aquifer

Question C.1:Why is the Ogallala Aquifer important to Kansas?
· Ogallala aquifer in Kansas provides for about 70% to 80% of water in the region highlighting its importance.

Question C.2: Why are we concerned about the Ogallala Aquifer?

· There is a lot of concern about Ogallala aquifer because of the large volume pumping which has led to declined water levels on the western part of Kansas.

Question C.3:A ‘renewable resource’ is an organic natural resourcethat can replenish to overcome usage and consumption. The water in the Ogallala Aquifer could be considered a “non-renewable resource” over human lifespans. Why?

· Ogallala aquifer may be considered to be anon-renewableresource because of the rate at whichthe water is drawn from the aquifer is much more than the recharge rate. If proper planning is not put into place, the water resource may be exhausted in the future.

Lab 18 Part D: Hydrocarbon Formation
Question D.1: What is the original source of hydrocarbons? In other words, where does coal, oil, and gas come from?

· Hydrocarbons are made from decayed lifeforms. These lifeformsare exposed to heat and pressure underneath the earth’s crust for long periods of time stretching millions of years; they are broken down into hydrocarbons.

Question D.2:What environmental conditions must exist in order to preserve the original material that makes up hydrocarbons?
· For the original materials that make hydrocarbons to be retained there must be high temperature and high pressure. This ensures that no other materials mix with the lifeforms.

Question D.3: A ‘renewable resource’ is an organic natural resource that can replenish to overcome usage and consumption. Why are hydrocarbons considered non-renewable resources?
· Hydrocarbons are considered to be nonrenewable because they cannot be replenished naturally in a short period. Given that it took millions of years for hydrocarbons to be formed it would take an equivalent time or more in the event they are exhausted hence they are considered nonrenewable.

References

El-nagar, Belal.Porosity and permeability.El HadiMazouz, 24 Oct. 2013, http://www.slideshare.net/belalelnagar3/porosity-and-permeability.

Society, National Geographic.Petroleum. National Geographic Society, 15 Jan. 2013, http://nationalgeographic.org/encyclopedia/petroleum.

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