|North Dakota fracking sites. They are located every quarter mile in|
some locations. Photo from Google Earth but credited to Glen Fredlund.
The series will consist of several parts:
Part 1. North Dakota
Part 2. Boom! Fracking and the Bakken Shale
Part 3. The Pipeline Project
Part 4. The Heart of the Matter: The Missouri River
Part 5. The Standing Rock Sioux
Part 6. The Legal Issues and the Protest
Part 7. Ethical Considerations and Conclusions
Part 2. Boom! Fracking and the Bakken Shale
As I made clear in yesterday's post on North Dakota, the state is undergoing tremendous population change as a result of the boom in the oil and gas industry. The population grew from 673,000 in 2010 to 760,000 today. In today's post, I will explore what is driving the boom by reviewing the geology of the oil and gas reserves and the technology of hydraulic fracturing (fracking). The growth of oil production in North Dakota is relatively new and transportation infrastructure is not present to move the oil around the country. The lack of infrastructure prompted the development of the Dakota Access Pipeline.
Shale is a clastic sedimentary rock. To understand what this means, let's break this down a bit.
|Click for image credit.|
Clastic sedimentary rocks form in stable depositional environments. Think about places today where sediment is actively deposited. There are some obvious environments such as deltas and river valleys. However, there are many others such as the base of ocean or mountain slopes, some deserts, tidal flats, lakes, and under glaciers. Regardless of environment, the sediments are brought to the site of deposition by water, wind, or ice which, in the case of water and wind, serves as a sorting mechanism for the sediments. Most clastic sedimentary rocks consist of highly sorted pieces of sediment. It is this regularity which gives clastic sedimentary rocks their properties.
|Shale. Click for photo credit.|
Sandstone consists of sediment that is between 2mm and 1/16mm in size. This common rock forms in a number of environments but is typically associated with marine and wind environments. Due to the nature of sand, the rock is typically very porous and permeable. Siltstone is made of silt-sized sediment that is between 1/16mm and 1/256mm in size. It has properties that are transitional between sandstone and shale. Finally, shale consists of very small sediment that is less than 1/256mm in size.
|Shale bedrock. Click for photo credit.|
Shale rocks tend to form in areas where there is a regular input of fine-grained materials without significant movement of water. They are found in deep deltaic or oceanic environments, deeper portions of lakes, or stable basins such as wetlands or swamps associated with coastal or riverine settings. What is important about these settings is that they tend to be organic rich environments. Very fine grained organic matter can get trapped in the sediment and become part of the rock via lithification.
Shales tend to be grey, black, brown or green in color. They are fissil, which means that they break into flat bedding planes. This fissility is a distinctive feature of shale that helps to distinguish it from siltstone. Shales have a very high porosity but very low permeability. In other words, the rock can store huge amounts of liquids compared to other rocks, but the liquids cannot move easily through the rock. In addition, it is difficult to pump liquids out of shale. Any oil or natural gas in shale was considered impossible to remove until the advent of hydraulic fracturing (fracking).
|In this image from NASA, one can easily see the lights associated|
with fracking in the northwest quarter of North Dakota. Note that
this is a very sparsely populated area of the state. Click for photo credit.
The Bakken shale is only found in the subsurface and what we know about it comes from cores and geophysical assessments. However, the most important aspect of the formation is that it contains up to 18 billion gallons of oil, which makes it one of the largest energy reserves in the United States. Fracking of the shale and the exploitation of the reserves started early in this century and continues today. It is one of the most recently exploited reserves in this country which has led to the boom in the North Dakota economy.
Fracking, a relatively recent technological advance for extracting oil from shale, is a relatively simple process and is explained below in this video from CNN.
Basically, fluids under pressure are pumped into the shale to release the oil and natural gas from the pore space. The controversial aspect of fracking is that the oil companies utilize a great deal of water and they do not inform communities about the composition of the fluids they pump into the ground. Because they do not explain what is going into the subsurface, there is mistrust about the process and about the outside companies in many areas because local people do not want their local water supply tainted by the chemicals that remain after fracking. In addition, there is concern over the migration of remnant natural gas and oil to local water wells. North Dakota, with its sparse population, has embraced fracking. However, New York, with its abundant population, has banned it. In addition, the advent of numerous earthquakes in Oklahoma has raised the question as to how fracking transforms geologic conditions in the subsurface.
|An oil pipeline in Alaska. Click for photo credit.|
The next post will focus on the Dakota Access Pipeline
1. How does shale differ from other clastic sedimentary rocks?
2. Define permeability and porosity. Why do you think these rock properties are important in the petroleum field? Using the Web, find out how porosity and permeability varies quantitatively from shale to sandstone. How much oil can shale hold in one cubic meter compared to an equal volume of sandstone?
3. Do a Web image search for a map of the Bakken Shale. Describe its extent.
4. What are the pros and cons of fracking?