Introduction
I am a geology major interested in mining and the region where I live and go to school, frack sand mining is a hot topic. Frack sand is a component used in the process of mining oil and natural gas in shale, and unconventional deposit, in a process called fracking. Also being in this position, I have heard of numerous geophysical and hydrogeologic studies that have indicated that fracking has caused groundwater contamination and earthquakes. This prompted me to create my semester long GIS II project around this contentious issue.
Background Information
Fracking is the process of injecting water, sand, and a slurry of chemicals at high pressures into shale units to release trapped oil and gas (Figure 1). This has led to a petroleum revolution in the states as there are 32 known oil and gas shale deposits, called plays, in the lower 48 states (Figure 2). The major states involved in exploiting these plays are California, North Dakota, Oklahoma, Texas, Wyoming, and Colorado.
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| Figure 1. The Fracking process. This figure details the controversial process of fracking. In addition of already being revolutionary, the invention and use of the horizontal drilling pipe has increased oil and natural gas production. Horizontal drilling pipes can even targeted plays up to two miles away. Note the chemical storage tanks and the location of a groundwater aquifer in relation to the shale.
Once the process of fracking has been completed there is a stew of water, oil, chemicals, and sand, called used water, sitting below the surface. This used water is usually pumped out and is then put in either storage tanks, like in Figure 1, or in lined ponds, but pumping does not always remove the liquid 100%. The larger issue is that there is no standard regulation for this used water across state lines. States like Wyoming and North Dakota have strict regulations for the handling of used water which includes storing the water in storage containers at the surface and then monitoring the tanks with wells to identify and cleanup leaks. In states like Oklahoma and Texas, there is very loose regulations. Used water often sits in leaking tanks or ponds. Sometimes it is not even pumped from the well and left at depth! This can cause contamination in groundwater and in surface water. It has even been suggested as the cause for increasing earthquake events and health issues in these states.
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Figure 2. Lower 48 states shale plays. This map details the different plays located in the lower 48. Most of these occur in sinks, called basins. Texas and Oklahoma have very large and abundant plays. The Utica and Marcellus shales in Pennsylvania have been, for the most part, depleted by traditional drilling. The Antrim, in Michigan, is undeveloped.Project Development and Question
With this knowledge, I wanted to focus on a state that looser regulations and had earthquake data. I initially chose Oklahoma. However, there was insufficient data. Instead I chose Texas. Texas had plenty of data and still had the looser regulations. My final research question was:
Using GIS software, is there a correlation between the shale plays and earthquake events in Texas? What areas in Texas are at the most risk of earthquake?
Literature Review
This literature review was designed to inform and help guide analysis of our individual project. I wanted to know what have been the impacts of these earthquakes to the state of Texas and if there were any similar projects done. Some of the impacts include:
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Figure 3. The results of the University of Texas-Austin's research. Their research was much more geology and exploration based, however they employed a GIS software to create the map seen above. Although railroad spurs are not shown in this map, this was the technique they used. This technique resulted in large quantities and trends of drilled wells used in fracking.Data Analysis and Procedure
I initially wanted to recreate the results from the University of Texas-Austin's study by importing a Texas map that included the counties. I then added a basins shapefile to show the locations of these shale plays. However, the basins shapefile was for the entire USA so the basins shapefile was clipped to the Texas shapefile. I then added a railroads feature class. With my prior knowledge, I knew that the Union Pacific railroad was the largest supplier of frack sand to drill sites. Using the select by attributes function I created an expression that selected only the Union Pacific spur lines, which I then created a feature class from. However, this was for the entire state so I wanted to remove unnecessary spur lines. From research, we know that horizontal drilling can target plays up to two miles away, so a 2 mile buffer was created around the basins shapefile. Any railroad spur that did not fall within or on the buffer or basin shapefile was removed. The editor toolbar was then used to create an extra column in the railroad attribute table using the expression "Union Pacific and Spur line*25." This was done to show the approximate location of drill pads. The results are below.
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| Figure 4. Replica of the University of Texas-Austin study. The red lines show the Union Pacific Railroads spur lines that fall within the buffer or basins shapefile. This was done to allow further analysis to continue. However, note the dissimilarities between this map and the results of the UT-A's work.
At this point I noticed discrepancies between my map and the results of the University of Texas-Austin (UT-A) study. To cross-reference my work, I found a table (not compatible with GIS) that detailed how many wells for oil and gas were drilled by Texas county. After doing the math, my number was nowhere close to the numbers I had from my map. At this point, I decided that I could not continue to do analysis using my map because it was incomplete and therefore inaccurate. I instead decided I would make conclusions based on the location of earthquakes and the basins.
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| Figure 5. A preliminary model of analysis for the rest of the project. This was adjusted for the railroad spur errors.
For the rest of the analysis, the main tools used were density and frequency tools. Frequency was reported in table format. To ensure accuracy, I wanted to do some steps of analysis in multiple ways. However, I did not have the time. It also should be noted that the Kernel Density Function did not end up being used as the process resulted in an error. All maps produced were reported in the NAD 1983 geographic coordinate system.
Results |
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| Figure 6. This map shows that for earthquake events, that occurred the past 18 years or since fracking has become more common, almost all earthquakes in Texas occur in the shale plays. This means that there is a correlation between fracking and earthquake events. This has the impact to negatively affect human health and cause massive damage to infrastructure. |
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| Figure 7. I now took that same map and applied a rank system to show different magnitudes of earthquakes. The results of this map shows that the frequency of earthquakes are more often in the Permian Basin but the largest earthquakes occur in the Western Gulf/Eagle Ford shale. |
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Figure 8. This last map shows cities with populations of greater than 200,000 in relation to the basins and earthquake events. The earthquakes in the Fort Worth and Western Gulf Basins have the potential to affect the greatest amount of people.Conclusions
From this research I am confident to report a correlation between earthquakes and shale basins in Texas. There is really no part of Texas that doesn't have the potential to be negatively affected by fracking. The earthquakes in the Permian Basin, although not the strongest, occur the most often and are the deepest. This means that infrastructure would have to be built to withstand repeated earthquake events. The earthquakes in the Western Gulf Basin are the strongest with the potential to cause significant damage to structures and harm human life. Finally, the earthquakes in the Fort Worth and the Western Gulf Basins occur in large, populated errors. This increases the risk for human injury and death. I would hope that these findings would prompt Texas lawmakers or the public to regulate fracking to a safer standard where the negative affects could be largely diminished.
Reflections
If I had additional time, I think it would be interesting to add a hydrologic component to the study and see if the locations of the drill pads are close enough to bodies of water to affect the water quality. I would also like the add the geology and see the impacts of geologic structures on earthquake events. I would have spent more time looking for additional data and finding other studies to base this one off of.
References
Data from this project came from the USGS, Texas-Drilling, the Texas Commission on Environmental Quality, and the Texas Natural Resource Information System.
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