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Thinking about Marcellus shale geology

June 16, 2010

I know I’m not the only geologist who, when studying the subject in college, spent a lot of time convincing my family that I could get a job as a geologist and that a huge part of what we understand about our world comes from geology. From that perspective, the journey into understanding and providing outreach on aspects of Marcellus shale gas drilling has been very fulfilling. Communities coming to understand how the geological character of their land is important, and wanting to learn more, has been refreshing. It has also been rewarding to dive back into the primary scientific literature to search for answers to the questions our local communities are asking.

Of course, no one has written scientific papers that specifically answer all of our questions. We’re in the middle of looking into lots of different issues concurrently, finding and reading numerous papers on each topic. For instance, to look into questions about induced seismicity (the potential for earthquakes triggered by drilling), we’re reading about the structure of the rocks here that contain the Marcellus shale and about potential examples of induced seismicity from drilling in other areas. But we’re also reading about induced seismicity caused by carbon sequestration, deep water injection wells, and other activities that have been suspected to induce earthquake activity. Because the geology of the Marcellus shale (like the geology anywhere) is unique, we must overturn all of these proverbial ‘rocks’ to explain what the science tells us today. Given the lack of data on the potential for induced seismicity for the Marcellus shale, studying examples from these other sources is the best way for us to predict what might happen.

While the past couple years may be the first time the general public has heard about the Marcellus shale, geologists have been researching aspects of it for a century or more. At PRI, we’ve been aware of it for a long time, too. In fact, our popular fossil collecting trips in the region take us to outcrops in the Hamilton Group of rock layers, the base of which is the Marcellus shale. Of course, we also know that the same conditions that make the Marcellus shale a rich natural gas deposit make it very fossil poor for collecting. Geologists have also known that there are other shale layers in New York State that are sources of natural gas, too. For instance, this past weekend the Ithaca Journal highlighted what it described as “new riches” that can be found in the Utica shale. Read the article HERE. As we’ve been gathering resources to answer people’s immediate questions about Marcellus shale gas drilling, we’ve been working hard to learn about the potential differences between Marcellus and Utica shales.

One thing we do know about all of our work to compile and make sense of the many scientific sources related to Marcellus shale gas drilling is that science is not certain. There is no ‘proof’ – that’s a term used in math. All scientists can do is predict, based on the best available data and research, what they think will happen. We call those predictions hypotheses. Sometimes there is a good chance that our hypothesis will be correct, and other times we’re less sure. But the more fact-checking we do, and the more angles from which we investigate an issue, the more likely we are to be correct. Here at PRI, we’re doing that fact-checking to help give the best scientific information we can to answer some of the many important questions people have been asking.

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2 Comments leave one →
  1. John Bullock permalink
    September 28, 2011 7:59 pm

    I have property in Southeast Steuben County, NY. Marcellus Shale, of course, is a hot topic here. I am curious if the Marcellus shale geology is consistent throughout its geological boundaries in New York or if some areas will not be economical.

    Thanks,

    John

    • prianditsmuseumoftheearth permalink*
      September 29, 2011 9:22 pm

      John,
      Great question. Marcellus geology is NOT consistent throughout its geological boundaries, so some areas will be more economical to drill than others. For a great extended read on this, I’d encourage you to go read our pamphlet Marcellus Shale: Why the Geology Matters at museumoftheearth.org/marcellusshale. You’ll find it under “The Marcellus Papers.” I’ll give a brief overview here.
      Where drilling will be most profitable is a combination of the amount of gas in the shale and the quality of gas in the shale. These depend upon the conditions under which the rock layer formed 390 million years ago in the Devonian and what happened to it between then and now.
      The Marcellus Shale formed in the basin of a shallow sea, which varied in depth throughout the basin. There were mountains forming on the northeastern shore of the basin, near where Albany is now. The deepest part of the sea was in the east, and the sea generally shallowed toward the west. The mountains forming to the east experienced a lot of erosion. This deposited a lot of sediment in that eastern part of the basin, so the Marcellus is also generally thickest in the east, and thins as you move west.
      In order for natural gas to form, marine organisms, like plankton, must settle to the bottom of a sea and not decompose. This happens when there are low oxygen conditions at the bottom of the sea. There was more oxygen in the western part of the sea, so more of the organic matter decomposed, leaving less natural gas there. The sediment that came in to the sea from the mountains eroding to the east also lessens the amount of natural gas, so the “sweet spot” for the formation of natural gas was in the between the western and eastern sides of the basin.
      After the Marcellus was deposited, it was covered by more sediment. As more and more sediment covered it, it the organic and non-organic material that make up the Marcellus shale was pushed down towards the center of the Earth, where the organic material was “cooked” by increasing heat, causing the chemical changes necessary to convert it to natural gas. Marcellus Shale gas is mostly methane (CH4), but other kinds of hydrocarbons are formed in this process as well, like ethane, butane, and propane. Varying amounts of heat and pressure, which are not constant over the whole basin, varies the amount of other hydrocarbons in with the gas. When it’s mostly methane, it’s considered “dry” gas, when there are a lot of other hydrocarbons, it is considered “wet” gas.
      Another factor determining whether or not gas can be economically extracted is the depth to the formation. If the Marcellus Shale is shallower than about 2,000 feet, hydraulically fracturing the layer for extraction is impractical.
      Taking all of this into account, here (http://www.pamatters.com/wp-content/uploads/2011/07/MarcellusShale2.bmp) is a picture of the region with the Marcellus shale and the Marcellus “fairway” outlined. The “fairway” is where the industry have determined gas drilling will be most profitable. That does not mean they won’t drill elsewhere, just that they believe this area is the best for drilling in the Marcellus, given the available data.
      Steuben County lies within the fairway, so you will probably see this become an even bigger topic in your community as the NY drilling policy is hammered out.

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