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Dave Russ:† First of all, I certainly like to thank you all for coming here tonight and welcome to the National Center, of the U.S. Geological Survey.† I'm Dave Russ, I'm the regional executive of the Northeast here at the USGS and we're excited, very excited to have you here at our evening lectures where we showcase some of the studies and research that our USGS scientists are conducting.
The Science in Action lecture series that this is a part of, is intended to give you a better understanding of the science behind the issues that affect our daily lives.† Tonight's lecture will be a panel discussion on hydraulic fracturing.† A question and answer session will follow, and we'll hold questions, if it's all right, until the final panelist has made his presentation.
I'm going to begin with just a very brief overview of what we're doing in the USGS regarding hydraulic fracturing to provide some context for you as a matter of introduction and before we begin, I would like to ask you to silence your cell phones if you have one so that it doesn't disrupt folks as we proceed here. Hydraulic fracturing has been a major topic in newspapers and magazines for well over a year or so now.† In fact, just today two articles in the Wall Street Journal describing issues and activities associated with it, so certainly something thatís in the public's eye.
However, hydraulic fracturing is not new.† It's a technique that's been used for decades by the energy industry to assist in extracting oil and natural gas from [unclear] rock and also used to enhance production of ground water in some wells.† So, it's been a tool that's been around for some time.
The process of hydraulic fracturing deals with injecting wells with large quantities of water, sand and chemicals at very high pressures.† Pressures high enough to break up the rock, and to allow trapped oil and gas to be extracted up the well.† Until the past decade, it was generally limited to conventional oil and gas deposits, but as you'll hear tonight, it's allowed a whole new industry to develop for unconventional oil and gas.
The development of revolutionary new technologies to drill horizontally to accurately steer the drilling bit is what's made hydraulic fracturing a more viable tool and technology attractive to explore for and produce unconventional oil and gas deposits, such as those trapped in shale rock, these shale gas deposits in tight sands are resources that are critically important for our nation.†These deposits are really a major new addition to our resource base and added significant availability of gas to the United States and to oil as well. In March 2011, the White House released a blueprint for a secure energy future, developed to reduce America's dependence on oil, to save consumer's money, to make the United States a leader in clean energy industries.
And although hydraulic fracturing is playing the key role of opening up a new class of unconventional oil and gas resources, it has also raised some concerns about possible negative effects that could be detrimental to the environment.†
The USGS has several critical scientific activities directly applicable to unconventional oil and gas resources related to hydraulic fracturing.† These activities are conducted in collaboration with many partners.† The USGS does not advocate for or against specific actions or procedures, rather we provide decision makers with unbiased scientific basis for planning, for establishing policy, regulatory and resource management decisions that are made by others.
The goal of our overall program focuses mainly on the timely policy relevant science, directed to research topics that could be most effectively and efficiently conducted to provide results and technologies to support sound policy decisions by state and federal agencies, responsible for ensuring the prudent development of energy resources while protecting human health, and the environment. Now tonight, we will have three speakers who'll each address various aspects of our hydraulic fracturing work but at this time I'd like to introduce our first speaker who is Doug Duncan.† Doug is the Associate Coordinator for the U.S. Energy Resources Program and Doug was first attracted to geology when his parents hauled him around as a kid collecting rocks on many different field trips, and after getting geology degrees from the University of Georgia in Penn State, Doug worked cleaning up nuclear waste in Washington State; also spent time looking for oil and gas as a geophysicist for Exxon; and managing environmental research in monitoring at the Nevada Test Site before coming to the USGS.
And Doug will address us tonight on the increasing role that unconventional oil and gas resources play in the nation's petroleum endowment.
Doug Duncan:† Thanks, David.† OK.† Welcome everybody, thanks for coming out tonight.† I'm going to talk about Unconventional Oil and Gas Assessments in the United States, and I want to talk about this for several reasons, one is to set the stage for the following two talks, but also just to give you an idea of what role hydraulic fracturing and horizontal drilling, directional drilling, play in enabling the production of these so-called unconventional resources.
And, I'll start out by saying that the nation is still very dependent upon fossil fuels including oil and gas and in particular, gas provides about 25% of the supply of energy that our country uses every day.† And this particular diagram shows about where that gas comes from, because it comes from different sources.† And on the left hand side of the graph, the data, the line in the middle is for 2010 and that's the most recent data that we have from the Energy Information Administration. And you can see that there's a number of different sources, some of these are conventional and some are unconventional.
And unconventional resources as Dave said are those that take a special technology like hydrofracking, horizontal drilling, directional drilling and others in order to produce from these very tight or very impermeable formations at depth.† And so the shale gas is one of those sources, tight gas that'd be sand and carbonates and other rocks, is other and coal bed methane is in the green there, is sometimes fracked in order to produce the gas.
The other sources are conventional sources and you can see that their are productions domestically of those sources is in decline.† And so that's why the long time use of hydrofracking for tight gas and in a more recent use of it for shale gas, is so important.† And to see, if you subtracted those wedges that we would have a much less domestic production and we would have to be importing that gas to replace that production.
The USGS then, our role is to try to, one of our roles is to try to assess how much undiscovered gas might be out there, yet to be discovered, using current geologic knowledge and technology.† And to go back to this slide, this is all, on the right hand side, is a projection.† In order to make that projection you need to have an assessment of how much gas is yet to be discovered.† So we've used standardized methodologies that are based on a geologic model that we prepare, and then we apply some statistical or probabilistic approaches to try to estimate how much gas might be out there yet to be discovered.
And that's an uncertain business which is why we use these probabilistic approaches, and we use, because of the transparency of our methodologies and the consistency of our methodologies, our assessments are used by a wide variety of people including land managers of our federal lands, our congress and state congressional delegations, for example, public nongovernmental organizations, as well as industry. So let me step back just a little bit so that we understand what an unconventional resource just a little bit better.† This diagram is sort of a cross cartoon, cross sections through the Earth.† Conventional oil and gas resources and pools or reservoirs that are constrained on the top and on the sides by impermeable zones, and they often have an oil-water contact or a gas-water contact and unconventional resources we technically refer to them as continuous resources.
We say that because the oil resource or the gas resources distributed continuously through the formation at depths and it's held in the rock because of that rock is sort impermeable or tight and that's why we need to use techniques such as hydrofracking and horizontal drilling to extract the resource.
One example of a resource assessment is our recently completed Marcellus shale gas assessment in the Northeastern United States being from this area, you've probably heard of it or maybe not.† But at the bottom, I list here what are mean estimate which was 84 trillion cubic feet of gas.† I also showed that it could have been our estimate could be as low as†43 trillion cubic feet or as high as 144 trillion cubic feet.† So again, this illustrates the uncertainty that's associated with some of these assessment methodologies, and these are estimates after all. What we do with these assessments after we're done? These maps that I show here, the lower right one is a compilation of the assessments that we have done of the number of unconventional gas resources in the United States and you can see that there's, maybe you can't read the number, but there's quite a bit of gas, it's over 600 trillion cubic feet.† And in the upper left is our map of the conventional resources.
And with the exception of the Gulf Coast and Alaska, there is not much left to be discovered.† That means that most of these basins are mature exploration provinces.†And there's simply not much left to be found.† And that is why that graph that I showed you on the first slide had declining production from those conventional resources and why the unconventional resources are so attractive as an exploration target. But this isn't the whole story.† I was just talking about onshore U.S. and State Waters, our sister bureau, at the Department of Interior, the Bureau of Ocean Energy Management, uses very similar techniques to the ones that we use at the USGS for estimating undiscovered resources offshore, the Outer Continental Shelf.
And that ends up being a fairly large resource and I want to point out that this is a conventional resource, so far no economic incentive to go to the expense of doing the hydrofracking and that's sort of thing offshore.† But when you put all of that together and I've sort of put it together here for our domestic undiscovered resources, adds up to over 1,400 trillion cubic feet of gas, itís a really substantial amount of gas.
If you noticed again on the first slide, I didn't point it out, but our domestic production is about 22 trillion cubic feet a year.† I want to change now from talking about gas to talking about oil.† We also do oil assessments, we do unconventional oil assessments because these type of formations sometimes, as well, contain oil and most commonly known one is the Bakken formation in the Williston Basin of North Dakota and Montana.
And that's illustrated here at about our mean estimate is about 3.64 billion barrels of oil, which is a substantial oil resource.† We still have not completed all of our assessments so this map will be updated over the next year.
I want to just turn briefly to this map from the Energy Information Administration to show that shale basins or shale formations occur throughout the United States, not everywhere, but looking at a map like this in combination with our resources estimates, gives planners, policy makers, an idea of where future production might occur in addition to the ongoing production that we have right now, and be able to predict where infrastructure might need to be built, for example, or where impacts might need to be mitigated.
I want to just leave you with this worldwide look, we talked about resources within the United States, undiscovered resources.† There's another category of natural gas, which is stuff we've already found.† So far, this Iíve just been talking about what we haven't found yet but weíre estimating is out there.† But what we have in terms of crude reserves in North America is about 346 trillion cubic feet of gas, but you can see that there are much larger reserves in other parts of the world, particularly Eurasia, Russia in particular, and the Middle East.
And then finally, just to give you an idea of what the change or the boom in production in some of these basins is, I can show you an animated map of the Williston Basin and the development of the Bakken formation.† And you can see the production history building on the lower left corner of that graph.
Dave Russ:† Well, as you can see, quite an increase in the number of wells just over a relatively few number of years.† Thank you very much, Doug, for the presentation.
Our second speaker tonight is Dennis Risser.† Dennis has been a hydrologist and ground-water specialist for the USGS in Pennsylvania since 1988.† He is currently working on projects to estimate ground water recharge rates, model ground water-surface water interactions and sample base-line water quality of streams and wells in some area, Marcellus shale gas development in Pennsylvania.
Dennis received the masterís degree from Indiana University, bachelor's degree from Miami University.† And Dennis, tonight, will discuss some of the major water availability and quality challenges associated with natural gas development with a focus on the Marcellus shale in Pennsylvania.
Dennis Risser:† Thank you, Dave.† I'd like to talk about some water issues tonight associated with the Marcellus shale, and Doug ended up showing the gas boom in the Bakken shale in North Dakota and Montana.† Similar things happening here in Pennsylvania where I'm from.† This map shows that in the last five years there have been 10,000 sites permitted for Marcellus shale wells in the state of Pennsylvania, and 5,000 of those sites have actually been drilled.
So, a significant boom in drilling is occurring, and associated with that are of course some related water issues.† Part of what's happening in Pennsylvania that's interesting is that, you know, that's a state that's not a stranger to oil and gas development.† But the northeast part of the state really has not experienced historic development of oil and gas resources.† So, everything's pretty new in the northeastern part of Pennsylvania.
So I'm going to talk about a few of the water issues that I think are interesting, that I'm hearing on the news and I'm hearing from across my desk.† And first is erosion and sedimentation.† So, erosion and sedimentation can occur well before any hydraulic fracturing occurs and before the well is drilled, we have to have a pad and an access road.† And you can see on this slide which is in a pretty undisturbed area in the state forest in Pennsylvania that the well pad is a significant footprint on the landscape.
Marcellus well pads tend to be pretty large compared to conventional oil and gas well pads.† This is about 3 to 8 acres depending upon how water is handled.† In this slide, you can see that the water actually is stored in a pond right off the pad.† The roads tend to be large to handle all the truck traffic that needs to go up and down transporting water and chemicals to the site.
You can see on this slide that a lot of well, at least in this case, the developments occurring on pretty rugged terrain so any surface disruption can easily cause erosion, sedimentation if proper mitigation is not done.† Now those very large well pads they concentrate the industrial activity to that one large disturbed area.† But they do have the advantage in that multiple laterals can be drilled from that same well pad.† So a lot of the shale can be accessed from one location on the surface that's disturbed.
In this case, you can see a well that's planned with five laterals, about three to five thousand feet in length, and I've heard of laterals going out as far as 9,000 feet.† This is a planned gas field build out in a state forest where you can see how the development can be planned in a way that doesn't create much of a footprint on the landscape.† This is a 9,000-acre development or lease, it's almost 15 square miles, it's going to be tapped with only 15 well pads on the surface.
So, to put that in perspective, a more conventional type of exploration or well field build-out using 80 acres centers, or 80 acre spacings of the wells will look something like this and there'll be 10 times or more well pads on the land surface.†
So the number of wells is a big deal, especially when you consider that each one of the wells has to have an access road and a pipeline which, again, you're disturbing the surface, you're causing forest fragmentation, and possibility of erosion, sedimentation.† Any way that the surface disruption can be minimized is a good thing, and gas operators are trying to do that in many cases.
Spill and leaks. Certainly something that's not restricted to the oil and gas industry, but it's definitely a water concern.† We have a lot of water being handled, injected at high pressures on these pads, chemicals are being used along with the water, lots of truck traffic to transport these materials, so lots of opportunities for spills and leaks.
On some of the pads that I visited or see the operators trying to mitigate the possibility of any leaks or spills by things like these liners and berms.† Here's an example of a pad where the water and the drill cuttings are held in ponds, surface ponds.† Course even if those ponds are lined, which they almost always are, you worry about is the liner leaking or are the ponds likely to be over the top.
What I've seen in the field, the wells that I've visited, have containerized all of their handling of water and drilling fluids, like the drilling mud.† So that these yellow tanks would be tanks that instead of having ponds, the tanks are holding the water onsite that's going to be used for the hydraulic fracturing. So then they can keep the water in close loop system and minimize any potential for leaks and spills.
Same with the cuttings, when you drill a well you're using a drilling mud that's down in the hole with the bit, and the bits climbing up the rock, and those rock cuttings come up.† Again, they try to containerize and keep the mud in a closed loop system where they could continually recycle the mud, drop the rock cuttings out, put those in the container, stabilize them, send them to the land fill.† In Pennsylvania, I'm told that Pennsylvania landfills take about a million tons of drill cuttings per year.
Hydraulic fracturing, that's what we hear on the news all the time, water concerns about the hydraulic fracturing procedure.† A lot of the issues, that I hear involve the amount of water that's used, which is considerable, the chemicals that are used along with the water and sand; what happens to that water once injected in the ground and what's the quality of the water when it flows back to the surface.
So Iíll touch briefly on those issues. The amount of water used for hydraulic fracturing according to Susquehanna River Basin Commission, averages is about 4.5 million gallons per well.† Most of its from surface water, mainly streams.† And even the 32% water that comes from public supplies, which is purchased from water purveyors, most of that's from surface water supplies too.
So very little ground water being used in Pennsylvania for hydraulic fracturing. † Here you see a holding pond that's being used to refilling it for use for hydraulic fracturing.† That pond holds five million gallons of water.† Each one of those trucks in the picture down below, actually those trucks are feeding into the pipeline that you see and the water's coming from the trucks into that holding pond.
Each one of the trucks is 5,000-gallon truck, so to get five million gallons of water there's a thousand truckloads of water needs to be used to fill that pond.† So I know where they're getting the water, for this particular well, is from Lycoming Creek, which is a 2.5-hour round-trip from this well site.† So you can see there's a lot of truck traffic on the roads associated with this shale gas operation.
Susquehanna River Basin Commission made this graph to put in context the total amount of water that they think is going to be used for hydraulic fracturing purposes in Pennsylvania and that's what you see in the yellow box there.† It's pointing to the uses by the gas industry that they've projected -- 30 million gallons per day.† And they've compared this against other water uses in the basin for water supply, energy production, recreation, etc.
And just to give you a perspective, that this is really not a huge amount of water for the Susquehanna Basin.† It's a pretty water-rich basin and it has other uses that are much greater than the shale gas would use.
However, the total water use is really not the issue.† The issue is where are you taking the water and when are you taking it.† So the location of the withdrawal is very important.† Here you see a withdrawal from a very small stream and you can easily imagine that if they put too many straws drawing too much water, you can easily dry up that small stream.
So Susquehanna River Basin Commission has certain places where surface water withdrawals are allowed to be taken, permitted withdrawal points, thereís over 170 of them in the Susquehanna Basin.
And as I mentioned, it's not just where you take the water but the timing, the time of year that you take the water thatís important.† Here you see a graph, called the hydrograph, showing stream flow in Lycoming Creek during 2011.† Now 2011 was the wettest year in history in Pennsylvania.† We had a very wet spring and a very wet fall, but in the summer, during July and August, was a very dry period, when Susquehanna River Basin Commission looked at the stream flow hydrographs and said, no, the industry cannot take any more water from 36 of these permitted withdrawal ponds.
So, I guess the answers the question is there enough water is yes, there's plenty of water, adequate water exists but now everywhere and not at all times.† Another question about the hydraulic fracturing that's in the news a lot is the chemicals that are mixed with the water and the sand, and sands used as the propant that you saw in that animation.† What are those chemicals, what are they consist of?
Recently, industries disclosed a lot more of the chemicals that they're using.† I got this information off of a publicly available webpage called FracFocus, and that was put together by the Ground Water Protection Council along with industry, so that as a portal, really, for disclosing the chemicals that are being used.† I just picked a well randomly in the Northern Pennsylvania and these were the actual percentages of chemicals used.
There was only 0.3% of the total volume that was injected were added chemicals.† Now 0.3% is not a very big percentage but when you put in 4.7 million gallons, turns out that that's about 11,000 gallons of chemicals.† So, significant chemical usage is happening here.
If you look at the circle on the right, I've broken down the chemicals and you can see that the acid fraction is, contributes probably three quarters of the amount of the added chemicals.† The acidís used to clean out the well that you saw in the animation where they perforate the casing and shoot into the rock, and they follow that up with an acid treatment to clean out the holes that they've made into the casing rock.
Some of the other compounds with the primary FracFocus are mainly compounds that are used to keep the holes open, so that they don't get clogged up with bacterial activity or just with [unclear].† So then you've injected the water in the fracking process, you release the pressure and then that water comes back, at least some of it comes back.† Again, the Susquehanna River Basin Commission says that between about 5 or 15% of the water that's injected comes back.
This graph shows the salinity of the water at different sampling points, or different times during the flow back.† So after the first day of flow back, this well was sampled and was found it had 19,200 mg/L of total dissolved solids. That's pretty salty.† Sea water is approximately 35,000 mg/L of total dissolved solids.
Then you can see as time goes on and this flow back water continues to come out at less and less volumes, the salinity increases dramatically.† So after two weeks where the flow back consists of hardly any of the original water probably that was put in, mostly the brine that exists naturally in the formation, very salty, six times the salinity of sea water. †
And then waste disposal, the water comes back as flow back then you have to dispose of it properly and the disposal's been the big issue.† Early in the shale gas play in Pennsylvania, by early I mean four or five years ago, a lot of the wastewater was being sent to municipal treatment plants, which really were not well-suited or designed to handle the flow back chemistry, the high dissolved solid loads.
So that practice has largely been stopped in Pennsylvania.† There are some industrial treatment plants that can treat the water to various degrees but there's not a lot of those.† I've toured one of the treatment plants and the polished water, which starts out as 200,000 mg/L water after it has been distilled, comes out as about 100 mg/L finished product, and then that can be disposed of safely through the municipal treatment plant.
A lot of water is sent to neighboring states for deep-well injection, at least that's been the case in the previous three years and the next speaker is going to talk more about deep-well injection.† A lot of the operators are telling me now that they're 100% recycling their frack water.† So they use the frack water in a job what returns to the surface they containerize, they do some treatment on it and then use it on their next well.† So that's a very encouraging development.†
This is a really nice animation from Southwestern Energy.† It shows what you like to see -- you've drilled the well into the target formation down at the bottom there, the Marcellus shale, in our case, you've isolated that well with multiple strings of steel casing and cement and producing red gas bubbles, in this case, from the Marcellus flowing up to the surface.
You notice that there are two formations that are above the Marcellus that also contain gas, shown by the little red circles, and that's a very common occurrence in Pennsylvania.† It's not just the Marcellus shale that has gas but there are lots of layered shales above the Marcellus, and some sandstones too that naturally contain small amounts of natural gas.† And in drilling for the Marcellus shale, the operators have to drill through those shallower gas producing units.
Sometimes, and what they want to do is seal those off. So that the small amounts of gas can't escape and contaminate the environment.† Here's an example of how that contamination could happen if the cement job on the well is not done properly.† This case, in the circular insert, you can see an illustration, a cartoon showing that the cement is not bonded properly to the well.† And that allows some of the gas to seep out of that shallow producing zone, move up the annulus of the well between the two casing strings that has not been cemented.† And then find its way out into the environment and maybe contaminate some fresh water.
So, the industry tries hard to prevent this.† This is what we call stray gas and its one way that gas can get into the environment.† It's not the only way, but a lot of the cases of gas migration that you hear about and are blamed on hydraulic fracturing are more likely caused by this kind of well construction.
So all of these issues I've talked about, people ask me what's the cumulative impact or cumulative effects of all those things put together, all those wells.† Well I don't know, but it's going to depend ultimately on the regulations.† The regulations have changed twice in Pennsylvania in the last couple of years so things I'm sure are going to be modified as time goes on.† Also action by industry, the procedures and practices that industry's been taking have changed over the last five years tremendously.
And also, monitoring and research.† That's where USGS comes in.† Monitoring the quality of our surface and ground waters is very important and of really fundamental importance is getting a snapshot of the baseline quality of these resources before drilling comes in.† You can see in Pennsylvania and some of these areas, well the horse is already out of the barn, it's tough to find, to collect baseline conditions now.
And also research.† Research needs to be done on a lot of issues where we really just don't know what's going on.† One example is when reducing chemicals, contaminants in the environment we need to find ways to fingerprint those contaminants so that we can identify what the sources are.† Are they naturally occurring or are they coming from a leak and gas spill? Next, [unclear]
Dave Russ:† Thanks very much, Dennis.† Our third speaker tonight is Bill Leith.† Bill is the associate coordinator for the USGS Earthquake Hazards Program here.† Bill is a seismologist who oversees the global earthquake monitoring and recording capabilities of the USGS.† Bill served as the USGS acting associate director for Natural Hazards in 2010-2011, and in the past two years Bill has been called upon many times where his expertise on the subject of triggered earthquakes, including those associated with hydraulic fracturing.
In just the past month, Bill has given several briefings on induced earthquakes to senior administration and congressional staff.† Bill joined the USGS in 1986 after receiving a doctoral degree in seismology and geology from Columbia University.† He served as chief of the USGS Special Geologic Studies Group, and as senior technical adviser to the assistant secretary of state for verification compliance with Nuclear Test Ban Treaties.
And Bill will conclude tonight's lecture by discussing how disposal of waste fluids through injection into deep rock formations can generate earthquakes.
Bill Leith:† Thanks, Dave.† So, induced earthquakes. Iíll also refer to this as triggered earthquakes or induced seismicity, all are basically the same phenomenon and it's been quite a hot topic as you probably know from just reading the newspaper in the last few years.† Within last year we've had, either likely or potentially triggered earthquakes from the disposal activity that Dennis talked about in Arkansas and southern Texas, southern Colorado, Oklahoma, West Virginia and Ohio.
And so it seems like sort of a new phenomenon certainly in the news lately but its actually not on this slide is to give you a feel for what's been a phenomenon known for more than 50 years now.† Here's a list of either the largest or the most significant earthquakes in several different areas and due to several different human activities around the world.† Starting with back in the 60s in Rangely, Colorado, injection experiments.† The Rocky Mountain Arsenal, I want you to remember this one.† This is the largest well-documented injection induced earthquake, 925.3.
In Uzbekistan, the former Soviet Union, three magnitude 7 earthquakes, not necessarily due to injection.† We donít know what happened there.† But certainly due to the human gas extraction activities in Gazli.
Water reservoirs, large water reservoirs also triggered earthquakes in Lake Mead in Nevada and Oroville in California and many other places around the world.
And also geothermal, the Geysers Geothermal Field where the injection of fluids enhanced the production of geothermal energy has resulted in earthquake magnitude 4.6.† And a few others that you probably have heard of.
So, it's not a new phenomenon.† In fact, we understand why this happens fairly well.†That itís just actually very difficult to predict when it's going to happen, and the research problem we're working on is what to do about it when it does happen.† Many of these as you see are related to injection activity and that's what I'm going to focus my remarks on tonight.
Those activities that humans are involved with that entail or involve fluid injection in depth for the waste, liquid disposal of all types, disposal into wells and into the earth, geothermal production as I mentioned, and as these three production activities, enhanced production activities, that Doug described tight shale gas, tight sand and coal-bed methane often involve fracking and the associated needs to dispose of formation water fluids, [unclear] that Dennis described.
Also in the future, sitting out there is carbon dioxide sequestration.† There are some pilot projects now that should carbon dioxide geologic sequestration become from a big activity in the United States in the future, this will involve the injection of large amounts of fluid into the Earth with the potential of triggering earthquakes. So through the Chesapeake video that you saw at the beginning, and Dennis' talk, I think you understand this process well now.† The formation where the gas is, is fracked and that fracking process may use a million or some millions of gallons of water in order to extract the gas.
This is not the process that triggers the earthquakes in the cases that we know of.† It does make very small earthquakes that actually can be diagnostic for the industry to learn how their fracking activity is going, is it achieving what they want to achieve in terms of the perforation or a fracturing of the formation.
But what occurs after the formation, after the rock is fractured and during the production stage, during that video which you saw with the little red bubbles bubbling up to the surface, is that water is returned to the surface.† This formation fluid, the brine that Dennis described, can be quite salty, and that has to be disposed of somehow.
In some cases, that can be recycled as Dennis described.† In other cases it can be sent to a water treatment plant.† However, in many cases, there is such a large volume of fluid that comes up of this brine, that it's not economic for that to be disposed of at a water treatment plants or to be recycled and itís disposed of through a disposal well. That process is illustrated in this cartoon of the fracking occurs, the formation fluid is returned to the surface, it's sent off to a disposal well where it's injected deep.† Typically, to a depth that is actually has the potential for storing enough energy to trigger an earthquake.
Most of the time that doesn't occur, that's really worth keeping it mind, even though we have some very noteworthy cases where it has occurred.† This can be very a large amount of fluid, and a fluid from several of the production wells may be tapped into the same disposal well, typically it's tapped in to the same disposal well.
I illustrate here what a wellhead looks like but also the other phenomenon here that's of interest is the trucking of this, which Dennis described for the fracking operation, there's also trucking that can be associated with the disposal operation.† And the earthquake that was triggered and all the earthquakes that have been triggered over the last year, in Youngstown, Ohio, that fluid that's being disposed of there is actually formation water, produced water from the fracking activities in Pennsylvania.† There's no fracturing in Youngstown, Ohio.
So, why does this happen?† I'll try to lead you through this in a simple way.† First, it's important to understand that once you get a few kilometers deep in the Earth, the Earth is everywhere stressed, and of course the Earth is pervasively fractured and faulted.† So, from stress measurements made across the United States we actually know that these natural stresses put faults and fractures close to failure.
There's the difference in the rate of earthquakes in the West and the rate of earthquakes in the east is not because there's no stress in the east.† It's because there's a much higher rate of defamation in California and Alaska, for example.
So the natural stresses put faults and fractures close to failure and then you inject water, any fluid, into the rock at depth, that forces the fluid along those fractures at high pressure and relieves whatíís called the effective stress on that fault.
Essentially, the fluid pushes the sides of the fault apart, which is easy to imagine.† But what it does is it allows that fault to slip more easily than it would have had it not been pressurized.† So the injection activity pushing large volumes of high pressure down, deep into the rock which has already stressed is what's allowing earthquakes to be triggered.
The formation of new fractures, that is the hydro fracture, is actually doesn't release very much energy compared to these larger triggered earthquakes.† The hydrofrack the earthquakes will typically be less than magnitude 2, and there would be lots of them, and they're not really a safety concern.† It's really the injection of the disposal or the fluids that have to be disposed of, that are a consequence of the production operation that has the potential to trigger earthquakes.
And I think I just made my last point.
So, is this a significant phenomenon in the United States?
And this graph, I'll try to walk through with you, just to try to point a little fact that it's a very significant phenomenon, in the seismicity of the United States, although it is localized, and of course the earthquakes have not been all that large.
But what my colleague, Bill Ellsworth from the USGS and others at the USGS office in Menlo Park, have done is a very simple exercise which is just simply to count the number of earthquakes.† And they're counting all the earthquakes in the central part of the United States between these two bars that are larger than magnitude 3, from 1970 through most of last year.
But this count does not [unclear]. It's just the number of earthquakes of any size that larger than magnitude 3.† And what you see here is a fairly constant rate of earthquakes from 1970 to about the year 2000.† That's about an average of 21 earthquakes per year and a fairly steady rate. And we believe that catalog complete through this magnitude level all the way back to 1970, so this is representative of a pretty stable process of earthquake generation in the central United States.† And what happens in about the year 2000, the turn of the century 2000 and 2001 is that great increase, as next shown by this green line here.† It actually increases by about 50%.
And we associate that, there's a large proportion of those that we might call excess earthquakes that are occurring in Colorado and are associated with the production of coal-bed methane.† Then, in about 2008, that rate goes up again, it goes up quite significantly.† In fact, it's more than seven times larger than the long-term average.† And this rate is something that really cannot be explained by any natural process.
During this time period, we don't have any large earthquakes in the central U.S. that have a large series of aftershocks, which would bump up the numbers.† This is pretty stable rate during this entire time of earthquakes, but then it jumps up at this very much larger rate.
So, this is what we interpret to be a human induced process and geographically it's majorly associated with these enhanced recovery activities that previous two speakers talked about.
Iíll give you an example of one of them.† This is the induced earthquakes near Guy, Arkansas and Guy, Arkansas is right here.† And the injection wells in the area, this is a shale gas play, enhanced recovery, fracking operation and disposal as was described earlier.† The triangles here that are numbered one, two, three, four, five through eight are the disposal wells in this area, not shown are the production wells and then these numbers with letters are actually seismic graphs that were deployed by the University of Memphis, one of our partners. And so these are recording earthquakes and the earthquakes are shown here in yellow and red and they represent a progression in time, the red earthquakes occurring earlier and then migrating down to the south along with this quite obviously a fault in the rock over a period of approximately a year and a half.† So the fault is well defined.† This fault has obviously been the conduit for the injected fluids and it's that fault that's responsible for having produced this magnitude 4.7 earthquake.
What makes this a particularly useful case of triggered earthquakes scientifically is that after the 4.7 earthquake, the Arkansas oil and gas commission halted the injection at two new wells and very promptly the earthquake sequence died down.† Thatís the kind of smoking gun that's very helpful to have when somebody says, how do you know, how do you know, that those events were triggered? How do you know that they are not natural earthquakes? Because there are natural earthquakes in Arkansas.
Well, the fact that that sequence died as soon as those wells disposal activities were halted by the oil and gas commission provides that evidence.† And then they started on the third well, injected fluids and the earthquakes started up again.† So we have a very well established case.† This is published in the current issue of Seismological Research Letters if you want to see the gory details.
So the research questions are these just to put them simply: Why do triggered earthquakes occur in some places and not in others?† There are 150,000 disposal wells in the United States that are permanent, of those about 40,000 of the wells are associated with the disposal related to oil and gas activities.† And yet we have only a dozen or so cases of significantly large triggers most of the wells that do this injection are not triggering earthquakes. Another question is then once the earthquake occurs, what you do you do?† These three questions are the management questions and they have a scientific basis which we're working on now, to try to define so that we can get to this stage down here what do you do to regulate or permit the activity even before or after a significant earthquake occurs?† What process change should be implemented?
So I 'm going to give you two end numbers of that sort of management challenge and one is a very optimistic one, which is held by some people who believe that the process can be controlled and that we can minimize the risk of triggering an earthquake from our disposal activity.
And that goes back to the very first line on my first slide, the experiment that was done in Rangely, Colorado.† This was an injection triggered earthquake experiment it was designed to determine whether or not an injection activity could induce earthquake and whether changes to the injection activity could ameliorate the earthquake hazard. † So there are variations in seismicity were in fact produced by controlled variations in the fluid pressure in a seismically active zone, and the results of this experiment are said to have confirmed the predicted effect of fluid pressure on earthquake activity and indicated the earthquakes may be controlled by manipulated fluid pressure in a fault zone.
So, I was asked this question, it was last year when the earthquakes were occurring in West Virginia, by one of the state managers responsible for permitting the activity, and not knowing what to do he had already decided that they were going to cut the volume in half, they cut the permit volume in half.† And the question is, is that adequate?† And in fact, in West Virginia the earthquakes have continued in the same area. So the other end number of this is really an open question and that's illustrated by this graph which shows the maximum magnitude of a documented sequence of induced earthquakes for many places all around the world.† This RMA, Rocky Mountain, GEY is the geysers in California, ASH is the Ashtabula, Ohio and so on.† And†these are distinguished by the cases of fluid injection and other causes.
The largest earthquakes that occurred in Gazli and Uzbekistan are those, back up here, the one that we don't know very much about.† But you see this trend that that trend is maximum magnitude propped up against the log, the dimension affected by the fluid injection.† Essentially, that is the area affected by the continued pumping of water into a single injection well or a set of injection wells. Essentially, this phenomenon, that dimension in which the earthquakes are triggered by the injection activity is a function of the volume of fluid that goes in.† And so what you see here is actually a correlation between the volume of fluid and maximum magnitude.
This would indicate contrary to the previous slide, that that more water fluid that you put down to hold the water waste is disposed of, the larger the potential of earthquake.† And that dilemma, that's the research question which USGS is trying to address now working with EPA, some case studies and we're also working on the theoretical side of the problem, which of these two end numbers is going to be defining of whether or not, once an earthquake occurs are there significant signs that a disposal site, one can alter the practice to minimize the risk.
So finally, if you need more information on the subject, I'm pointing you to our website.† We have a Frequently Asked Questions set for earthquakes that are induced by fluid injection, that may answer some of the questions that you might have.
Title: Science or Soundbite? Shale Gas, Hydraulic Fracturing, and Induced Earthquakes
Hydraulic fracturing is the process of injecting wells with water, sand, and chemicals at very high pressure. This process creates fractures in deeply buried rocks to allow for the extraction of oil and natural gas as well as geothermal energy. USGS scientists discuss the opportunities and impact associated with hydraulic fracturing. Doug Duncan, associate coordinator for the USGS Energy Resources Program, addresses the increasing role that unconventional oil and gas resources play in the nation's petroleum endowment. USGS hydrologist Dennis Risser discusses some of the major water availability and quality challenges associated with natural gas development, with a focus on the Marcellus Shale in Pennsylvania. Bill Leith, associate coordinator the USGS Hazards Program, concludes by discussing the potential connection between disposal of waste fluids from hydraulic fracturing and earthquakes.
Location: Reston, VA, USA
Date Taken: 4/4/2012
Video Producer: Melanie Gade , U.S. Geological Survey
Note: This video has been released into the public domain by the U.S. Geological Survey for use in its entirety. Some videos may contain pieces of copyrighted material. If you wish to use a portion of the video for any purpose, other than for resharing/reposting the video in its entirety, please contact the Video Producer/Videographer listed with this video. Please refer to the USGS Copyright section for how to credit this video.
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