Eric Potter explains what, how and why of hydraulic fracturing
Natural gas is a major source of the energy we all use everyday. It’s found deep underground, often in the company of oil. In recent decades, conventional natural gas deposits have been the most practical and easiest to produce. Now new technology as enabled a boom in unconventional natural gas not possible a decade ago via a technique known as hydraulic fracturing, or fracking. Industry estimates suggest that $20 trillion will be spent on obtaining unconventional gas and oil between the years 2012 and 2035. Geologist Eric Potter of the Bureau of Economic Geology at the University of Texas at Austin explained the basics of unconventional natural gas – the what, how and why of fracking – with EarthSky’s Jorge Salazar. This interview is part of a series, made possible in part by the Bureau of Economic Geology at the University of Texas at Austin.
The past decade has seen a dramatic rise in use of unconventional natural gas. What is it?
Let’s talk about what natural gas is, and then get to the unconventional part. Natural gas is essentially methane. It’s a hydrocarbon gas that’s odorless, colorless, and it burns with a lot of energy.
It’s important to distinguish natural gas from gasoline. The public often mixes up the two. Gasoline is a liquid refined product. And natural gas is a gas.
Unconventional natural gas is natural gas that’s obtained from what we call tight rocks. Those are rocks that need to be cracked or fractured for the gas to come out of them.
It’s coming from the type of rock that we drilled through routinely – on the way to other objectives – when we were looking for conventional targets containing oil and gas in the subsurface.
We knew there were certain zones that when you drilled through them yielded a little bit of gas. But industry was never able to produce enough gas from those zones to make a commercial well, until recently.
So there’s nothing distinctive about the gas itself. It’s unconventional because it comes from rocks that wouldn’t yield any gas flow until recently.
And who uses natural gas?
We all use it. Natural gas is piped directly into more than half the homes in the U.S. for heating purposes via a pipeline system that’s over a million-and-a-half miles in length.
Natural gas is used mainly for electrical power generation and also for industrial uses like the production of brick, concrete, steel and glass.
And it’s also a raw material in the manufacture of certain substances like paints, fertilizers, plastics and medicines.
So what’s changed? How is unconventional natural gas accessed today?
The first difference has been the use of horizontal wells. You can imagine drilling a vertical well, maybe several thousand feet deep. And then the well is turned sideways within the target zone. A horizontal well typically will be drilled several thousand feet horizontally.
The second crucial technology is the hydraulic fracturing – or “fracking” – operation that takes place in that horizontal well. Hydraulic fracturing has been around for decades, but it’s been used in combination with horizontal well technologies in recent years.
Within a horizontal well, there are several hydraulic fracture jobs that take place. For instance, there would be one hydraulic fracture job pumped out near the end or the toe of the well. And then several more proceeding back toward the heel or where the well turned from vertical to horizontal.
You have multi-stage hydraulic fracturing in horizontal wells and that’s what’s different. In the old days – meaning 15 or more years ago – the norm was to simply drill a vertical well, down to the target, and complete the well to flow from that target zone.
And if you wanted to drill additional wells nearby, each of those was its own separate vertical well with its own drill site and its own road leading to that drill site. You can see that the surface impact of the former way of doing things would have been considerably greater.
When we’re talking about the notion of horizontal wells and the fact that multiple horizontal wells can be drilled from a single surface location, what you’re talking about is each of those wells maybe has its surface location a few feet from the previous one. So you drill one well, then you move the rig over twenty or thirty feet and drill another well. And that new well, again, it consists of drilling several thousand feet of vertical hole and then the well turning horizontal within the target zone. The difference is that the new horizontal well actually goes out in a different compass direction.
If you’re looking down on this from above and you could see what’s going on in the subsurface, you would see these horizontal wells spreading out like spokes of wheel. In other words, they can develop a large subsurface area from a single surface location.
So I know you and other geologists are excited about this. Why?
Mainly because there’s a great deal more of this unconventional natural gas then we first thought. It greatly augments the supply of natural gas that we thought was available to consumers, say, 15 or 20 years ago.
Unconventional natural gas has made a big addition to daily production amounts in the United States already. But why should we care? Natural gas is a tremendously versatile substance, providing relatively clean heating of homes and businesses, the fuel of choice for cooking, and a cheap source of energy to fuel electrical power plants. The ability to fuel more power plants with natural gas rather than coal is a game-changer. Our appetite for electricity keeps going up. The electricity has to come from somewhere. For power generation, natural gas has a number of environmental advantages – much less acid-rain-precursor emissions such as sulfur dioxide and nitrogen oxides, essentially no mercury emissions, and only half the CO2 emissions compared to coal. Now that industry has found decades worth of new reserves of natural gas in the unconventional reservoirs, the stage is set for transformation in the power generation sector, and potentially even in the transportation sector. Major metropolitan bus fleets already run on natural gas, and it would not surprise me if large truck fleets were to follow. And, largely unappreciated by the public, natural gas is a key ingredient in many industrial processes, including the manufacture of plastics. Walk into a sporting goods store or a car dealership. All you see is plastic. When you see that, realize that much of our highly-dependable equipment, from computers to airplane wings, comes from plastic, which comes from natural gas. Natural gas is underappreciated by the public, I suppose because you can’t see it. But it greatly affects our everyday lives, and has the potential to play an even larger role.
How much unconventional natural gas is out there, in the U.S. and the rest of the world?
At reasonable price forecasts, and assuming today’s consumption rates in the United States, there are several decades of unconventional natural gas available to us, using these technologies. So that’s a very significant addition to the nation’s resource base.
If we’re talking internationally there are many more unknowns. That’s because the United States, for a variety of reasons, is probably a decade or more ahead of other countries in terms of assessing and developing unconventional gas resources.
Bottom line, it’s a little too early to tell how much unconventional natural gas is present in the rest of the world. But based on what we know in the U.S. we expect the number to be high. The uncertainties are that not every shale or tight sandstone works as a target for this type of extraction. So, you want to be careful when making forecasts about places that haven’t really tried it with modern technology yet.
But there are environmental concerns. Can you briefly address some of them?
All energy resources have their pluses and minuses with regard to environmental concerns.
Let’s talk about the climate change issue first. Coal is a key part of our electrical generation capacity right now because we have a lot of it, and it’s cheap.
On the other hand, it’s recently been shown that there’s a lot more natural gas than we thought. And natural gas burns more cleanly than coal. For a given amount of electricity generated you have less of the greenhouse gas carbon dioxide going into the atmosphere with natural gas.
You also have fewer of the precursor chemicals to acid rain. And you have less mercury.
Most people would regard those attributes as a plus for natural gas.
What’s the biggest environmental issue, in your view?
Perhaps the largest environmental issue in unconventional gas development is surface disturbance. And by that I mean, simply the disturbance to the soil and to the surface in preparing pads for drilling, roads to those pads, road networks, pipelines to take the produced product to market. Plus other activities, including getting water to the drill site for the hydraulic fracturing process.
Along with that, road traffic has also been a contentious issue in many of these areas because you have trucks bringing the drilling rigs, the hydraulic fracturing supplies and so forth.
I think significant progress has been made in addressing some of these surface issues. For instance, now it’s possible and it has been done that in some cases 24 wells have been drilled from a single surface pad or surface location. That reduces the number of places that need to be leveled and have a road to them for drilling purposes.
There’s also been progress made in moving water from where it is stored, in a pond for instance, to where it’s used at a well head where hydraulic fracturing is taking place.
Typically this is now done by temporary pipelines from the source to the well. That reduces the number of trucks on the road hauling water.
When all is said and done, the surface disturbance issue will be perhaps one of the most controversial ones. In individual unconventional gas wells, the production declines very rapidly. To keep the overall production rate up, you have to constantly be drilling new wells. That means more locations, more roads, etcetera. The number of wells is significant and therefore the amount of surface disturbance is something that needs careful attention.
So, despite environmental concerns, you’re saying that unconventional natural gas is worth pursuing.
To me, unconventional natural gas is simply a sign of the times.
We lead energy-intensive lives, and that energy has to come from somewhere. By finding that we can produce this gas from rocks that ordinarily wouldn’t give up the gas, we’re demonstrating that when supplies are tight and prices rise to a certain point, then ingenuity can provide a new resource by looking at new possibilities.
Unconventional gas is available now. It’s cleaner than some of the alternatives in power generation. And it could play a significant role in powering the economy while we’re waiting for alternate sources of energy, like solar, to become available at meaningful scale.
Bottom line: A geologist’s perspective on fracking and why it’s being used to obtain energy. Interview with Eric Potter of the Bureau of Economic Geology at the University of Texas at Austin. Watch for an interview with geologist Ian Duncan on the environmental effects of fracking, coming soon.