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Fracking and the Geology Behind It

This conversation surfaced while speaking with a relative in another state a few weeks ago:

Relative: Vi, do you know anything about this new technology called fracking?

Vi: I do know a little about fracking, and I know enough to tell you that it is not a new technology. Fracking, or hydraulic fracking as it is properly called, has been around since the 1940s, however, new equipment has been introduced that makes the process more effective.

Relative: Aren’t you a chemical engineer?

Vi: Yes.

Relative: Can you explain to me how fracking works? And in a way that I can understand it? One of the things I am confused about is why some people seem to love it, and others hate it.

Vi: That’s a good question and one that, hopefully, will turn into a blog post someday! I have been looking at new developments in alternative energy, and I had already planned at some point to discuss fracking in this blog.

Well someday is today for my first post on fracking. Numerous articles, reports, posts, studies, etc. have been published on fracking, and the subject has received a lot of coverage in the news, especially the last two to three years. To better understand what it is and isn’t, and why it is important in today’s energy discussion, it is also important to know something about:

  • the geology behind fracking.
  • the origins of the fracking process and recent technological enhancements.
  • concerns from critics and supporters.
Source: NASA Image Gallery

Source: NASA Image Gallery

This post focuses on the geology of the earth, and some of those difficult and hard to mine energy sources that are found below the surface.

The Earth’s Interior

When we think of planet earth, most of us think of it as a big blue marble (see photo insert, courtesy of NASA). We visibly see the crust – that part of the land or continent that we live on – however, the rest of the interior of the earth is usually forgotten until there is an earthquake or sub-surface discovery.

Planet earth is made up of three primary shells [Ref 1]:

  • the crust
  • the mantel (upper and lower)
  • the core (inner and outer)
Source: USGS

Source: USGS

The core and mantle are almost equal in thickness, however, the core actually forms only 15 percent of the earth’s volume, whereas the mantle occupies 84 percent. The crust makes up the remaining 1 percent.

Rocks Tell the Story

Earth science is used to study the earth. The four primary areas of earth science are geology, meteorology, oceanography and astronomy. Geology, which means “study of the earth”, addresses the composition of materials, structures, and processes. Geologists are concerned about the origins of the planet and how it has changed over time. Geologists also search for fuels and minerals, study natural hazards, and work to protect the environment.

The earth is made of rock.  Thousands of different types of rocks and minerals have been found on the earth in the highest mountains to the lowest oceans. Rocks are continually changing. Wind and water wear them down and carry bits of rock away; the tiny particles accumulate in a lake or ocean and harden into rock again. By studying how rocks form and change, scientists have developed a very good understanding of the earth we live on and its long history.

Three Basic Rock Types [Ref 2]: Geologists have figured out a way to reduce thousands of different rocks into three basic categories:

Igneous Rocks – these are crystalline solids that form directly from the cooling of magma. This is an exothermic process (it loses heat) and involves a phase change from the liquid to the solid state. The earth is made of igneous rock – at least at the surface where our planet is exposed to the coldness of space. Igneous rocks are given names based upon two things: composition (what they are made of) and texture (how big the crystals are).

Source: geology.com

Source: geology.com

Sedimentary Rocks – in most places on the surface, the igneous rocks that make up the majority of the crust are covered by a thin veneer of loose sediment, and the rock that is made as layers of this debris get compacted and cemented together. Sedimentary rocks are called secondary, because they are often the result of the accumulation of small pieces broken off of pre-existing rocks. There are three main types of sedimentary rocks [Ref 2 &3]:

  • clastic sedimentary rocks such as breccia, conglomerate, sandstone and shale, that are formed from mechanical weathering debris.
  • chemical sedimentary rocks such as rock salt and some limestones, that form when dissolved materials precipitate from solution.
  • organic sedimentary rocks such as coal and some limestones that form from the accumulation of plant or animal debris.

Metamorphic Rocks – the name comes from “meta” (change) and “morph” (form). Any rock can become a metamorphic rock. All that is required is for the rock to be moved into an environment in which the minerals of the rock become unstable and out of equilibrium with the new environmental conditions. In most cases, this involves burial which leads to a rise in temperature and pressure. The metamorphic changes in the minerals always move in a direction designed to restore equilibrium. Common metamorphic rocks include slate, schist, gneiss, and marble.

So far, we know a little about the interior of the earth, and a bit more about the three types of rocks. How does that lead us to fracking?

Formation of Fossil Fuels

According to geologists, fossil fuels were formed over a period of hundreds of millions of years in the inner part of the earth’s crust. Fossil fuels comes from geologic deposits of organic materials, formed from decayed plants and animals that have been turned into crude oil, coal, natural gas, or heavy oils through the process of heat and pressure in the earth’s crust. (Some additional background information on how fossil fuels are formed can be found in an earlier post: Energy Sources in the U.S.)

Example: Oil shale

Example: Oil shale

Coal, shale, shale oil, shale gas, and oil sands are all classified under organic sedimentary rock. These energy sources are deposited within the rock, and are mined or extracted for their heating content. All can be difficult to mine and here in lies the problem and the need for fracking to capture the energy source.

Oil shale is a rock that contains significant amounts of organic material in the form of kerogen. Up to 1/3 of the rock can be solid organic material. Although drilling can extract large amounts of oil and natural gas from the reservoir rock, much of it remains trapped within the shale. This oil and gas are very difficult to remove because it is trapped within tiny pore spaces or adsorbed onto clay mineral particles that make-up the shale.

Oil sands, also known as “tar sands,” are sedimentary rock composed of sand, clay minerals, water and bitumen. The oil is in the form of bitumen, a very heavy liquid or sticky black solid with a low melting temperature. Bitumen typically makes up about 5 to 15% of the deposit. Most of the world’s oil sand resources are located in Alberta, Canada.

Example: shale gas from Marcellus Formation

Example: shale gas from Marcellus Formation

Shale gas is natural gas that is found trapped within shale formations. The ability to extract larger volumes of shale gas via enhancements to the fracking process is what has created a lot of buzz on this topic. The photo to the left is of a polished section of Marcellus shale in reflected light (source: www.geology.com). The gold particles are pyrite grains which are common in organic-rich rocks. In 2000, shale gas provided only 1% of U.S. natural gas production; by 2010 it was over 20% according to the Energy Information Administration. It should be fairly obvious to the non-technical types why shale gas and fracking have received much attention recently.

The next post will take a look at the origins of fracking, the fracking process, and the recent enhancements that have significantly increased the supply of available natural gas in the United States and other countries.


  1. The Interior of the Earth by      Eugene C. Robertson, http://pubs.usgs.gov/gip/interior/,
  2. Geology.com, Rocks, http://geology.com/rocks/
  3. Ask Geo Man, http://jersey.uoregon.edu/~mstrick/AskGeoMan/geoQuerry13.html



About Vi Brown

Vi is principal and CEO of Prophecy Consulting Group, LLC, an Arizona firm that provides business and engineering services to private and public clients. Prior to establishing her consulting practice in 2001, Vi worked with Motorola, Maricopa County Government, Pacific Gas & Electric, CH2M Hill, and Procter & Gamble. As an adjunct faculty member, Vi teaches undergraduate calculus classes and graduate level environmental courses. She is also a professional speaker.


10 thoughts on “Fracking and the Geology Behind It

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  8. Moderador Hola, me gustaría contribuir a este tema. ¿Puedo hacerlo? Prefiero preguntar como en otro foro que hice un buen aporte, pero el moderador chosed a moderada hacia fuera.


    Posted by Henrietta Sneath | July 4, 2013, 4:25 am


  1. Pingback: Fracking’s Early History | BridgeBizSTEM - December 28, 2013

  2. Pingback: Fracking’s Game Changing Technology | BridgeBizSTEM - April 18, 2014

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