Porosity and Permeability Lab
Earth Science Extras
by Russ Colson
Water Well on the Plains of Kansas, on the farm where I grew up. One of my chores was to open up the wind vane and release the brake to water the cattle after school!
Online learning can capture some aspects of doing science as a practice--some elements of arguing from evidence, elements of explaining models or applying those models to solving problems or explaining phenomena. However, one of the hardest aspects of science as a practice to include in an online experience is the actual doing of experimental or observational science. In a real lab, you have to figure out what to do, you have to figure out what to notice, you have to figure out what those observations tell you about the universe. When the lab is given to you as in an online experience, you are told what to do and even what you are supposed to notice. This limits the lab experience to only the final step of interpreting the results. To give you as much lab-like experience as possible, you should not only watch the following videos, but record the key data in writing, and then interpret the results. You will need the data to complete the following questions and to understand the lab.
Measurement of Porosity--effect of different types of sediment
Watch the experiment below, recording all data. Don't make sloppy recordings--record values carefully, including proper units of measurement, and organize the data into a table or chart that you can easily read and interpret.
Ideally, you can see the experiments in the videos below and create your own data table. However, to encourage you to take the time to do a good job with this lab, I provide example data tables for you to print and fill out in the file Preparation_for_Porosity_and_Permeability_experiments.pdf
Although the video does not show repetitions of the measurements, for the following puzzles, assume that multiple repetitions reveal that the 2-sigma experimental uncertainty in the measurements is about plus or minus 10% relative, meaning, for example, that, for a measurement of 50% porosity, the 'true" value has a 95% chance of being between 45% and 55%.
For the following questions, you must do the data analysis based on the data that you have taken from the video and written down in a table. Do not repeat these questions to get better answers--get them right the first time. Although repetition has been a valuable excercise in the previous interactive texts, it does not provide a meaningful learning experience in this case where the purpose is to practice interpretating and manipualting data, not getting a right answer.
Measurement of Permeability--effect of different types of sediment
Watch the experiment below, recording all data. Don't make sloppy recordings--record values carefully, including proper units of measurement, and organize the data into a table or chart that you can easily read and interpret.
Ideally, you can see the experiments in the videos below and create your own data table. However, to encourage you to take the time to do a good job with this lab, I provide example data tables for you to print and fill out in the file Preparation_for_Porosity_and_Permeability_experiments.pdf
Video of Permeability Measurements
Remembering our formula for discharge in ground water from the previous part of this lesson (reproduced below), calculate the permeability for each of the sediments (in Darcies). Darcy is the unit of permeability when the area, distance etc are in units of centimeters (or square centimenters, as appropriate), and the pressure difference is in atmospheres. Note that a cubic centimeter and a milliliter are the same volume.
Q= Discharge (in cubic cm per second) = P (in Darcies) * A (in square centimeters) * f (in atmospheres) / L (in centimeters)
Solving for Permeability gives us the following:
P (in Darcies) = [Q (in cubic cm per second) * L (in cm)] / [A (in square cm) * f (in atm)]
You need to get all of the values from the experiment in the video, which you should have already compiled into a chart or table-- except that I have done the calculation of the pressure change for you. The pressure at the bottom of the sediment is 1 atmosphere and the pressure at the top of the sediment is 1 atmosphere plus the weight of overlying water. The average pressure drop is about 0.0172 atm.
Make sure you have the calculations correct--don't answer the following questions until you're sure. Have you calculated A (area) correctly? Check the formula for area of a circle if you need to. Have you calculated Q (discharge) correctly? When you're sure, answer the following questions. These questions are worth more points and you shouldn't expect to go back and "correct" them.
Understanding Experimental Design
last updated 9/13/2022. Text and pictures are the property of Russ Colson.