[Subjectivist]

Maybe the term injection is the problem, if these wells are all gravity flow them whatever goes into the formation has to be able to move through the pores in the formation faster than gravity pulls it down.

[Hawkcreek]

Maybe the term injection is the problem, if these wells are all gravity flow them whatever goes into the formation has to be able to move through the pores in the formation faster than gravity pulls it down.

Maybe there really is a hole, a hole, a hole in the bottom of the sea? -- or the earth, in this case.
I tend to believe that voids will eventually be filled, if pouring enough into them, for long enough.
Then you have a void with thousands of pounds of pressure on the bottom of it, that were not there originally. Might even cause quakes.
The result is the same, whether you call it injection or "gravity flow well".

[Tanada]

Maybe the term injection is the problem, if these wells are all gravity flow them whatever goes into the formation has to be able to move through the pores in the formation faster than gravity pulls it down.

Maybe there really is a hole, a hole, a hole in the bottom of the sea? -- or the earth, in this case.
I tend to believe that voids will eventually be filled, if pouring enough into them, for long enough.
Then you have a void with thousands of pounds of pressure on the bottom of it, that were not there originally. Might even cause quakes.
The result is the same, whether you call it injection or "gravity flow well".

I would think that people planning a saline layer injection site would study the cores bored down to the aquifer to see where the water table is in relation to the cap rock that traps the saline water. That should provide them an excellent estimate of how much capacity the unsaturated section of the aquifer reservoir rock remains exploitable before the location is "full".

[ROCKMAN]

Sub/Hawk - Well, I did it again: forget to point out the obvious. Obvious to me but not to most here. Yes: "injection" may have been a much more loaded term then I was thinking. Easy for some, like the Apeman, to confuse "injection" with "frac'ng". Not only are the two not the same they are almost polar opposites with respect to what happens in the earth. Frac pressures are designed to be much high then the formations they are “injected” into: otherwise how could the crack those rocks open. Injection (disposal) wells are specifically design to NOT FRACTURE the rock. Great efforts are made not to do so but not for any environmental reason: it would destroy the value of disposal wells. Wells that not only cost $1+ million but are also needed to commercially produce high water cut oil reservoirs.

Hawk – No, the disposal wells do not continually increase reservoir pressure as those fluids are injected. First, if the original bottom hole pressure is 1,600 psi (we all do know that all reservoirs have pressure in them that is essentially determined by their depth, don’t we?). For instance the reservoir I’m disposal water into in Victoria Co. Texas is at 3,800’. The original BHP (bottom hole pressure or reservoir pressure) is about 1,600 psi. If I had a hole in the round down to that reservoir and filled it with salt water the pressure from that column would be about 1,600 psi at the bottom of the hole. And that’s with me NOT pumping the fluid…just the force of gravity. It’s no different if you were to dive into the ocean to 3,600’…same pressure. In order to inject water into that big porous sand I have to add a few hundred psi at the surface to increase the BHP above 1,600 psi to get the formation to drink the water. And no: the velocity of the water moving through that 80’ thick sand is much slower than the velocity of that water going down a 3” diameter tubing. If it were I would run the risk of FRACTURING the reservoir and ruin the utility of the disposal well.

IOW if I were to inject into the disposal zone at a much higher pressure (like the 10,000+ psi they use to frac wells) it would fracture the sandstone reservoir and destroy its ability to take water. Remember the huge difference between a shale reservoir and a high porosity sandstone reservoir: the shale doesn’t flow naturally while the sandstone does. A frac’d well has to have proppant injected into it to hold the fractures open. In a disposal well not only do we not pump proppant down with the water we actually filter out all particular matter. Even the stuff too small to see with the naked eye. And that also includes miscroscopic oil droplets. And again not because of environmental reasons. In time those invisible particles, including oil on the order of 10 parts per million, would plug the pores of the sandstone reservoir and eventually so inhibit the injection process that the $1+ million disposal well become worthless. And the oil production of the high water cut formation is lost.

So again just to be very clear: the increase in reservoir pressure from a disposal well is usually just a few hundred psi above the existing natural reservoir pressure. All those disposal wells in OK are not increasing the subsurface pressure by any significant amount. Frac’ng a well does induce very high pressure into the rocks. But hopefully for the last f*cking time: even the folks who think they see a correlation with the tremors in OK ARE NOT pointing their finger at frac’d wells but are talking about disposal wells. LOL.

So while the Apeman can try all he wants to highjack the discussion of DISPOSAL WELLS with chatter about frac’ng and frac fluids let’s stay focused on the subject of this thread: disposal wells and increased seismic activity. Nothing wrong with discussing the aspects of frac’ng…that’s why we’ve had many threads devoted exclusively to the subject. But this isn’t one of them.

So now let’s try that really f*cking simple question one more time: If there have been thousands of disposal wells injecting TRILLIONS OF GALLONS of fluid into the OK subsurface for decades before the recent increase in tremors why are they only seeing that increase now? Again look at great chart showing tremor activity in OK for the last 25 years. See the radical increase by 2009? Now in your mind’s eye add trillions of gallons of water being inject from earlier when the chart starts through today and explain why we we’re seeing so few tremors before 2009 compared to post 2009 if, in fact, they were caused by the same disposal wells?

So again: it’s a very obvious chart and a very simple answer IMHO: why an increase in 2009 and not before?

[Hawkcreek]

Sorry, but this one I don't buy. You say that the bottom formation pressure does not increase no matter how much fluid you pour into the formation -no matter how much the formation may or may not have been filled before you started, no matter how high a column of fluid you stack on top of what may have been there originally ------nope, I don't believe it.
You also seem to claim that most disposal wells are just a simple pour-in type. I don't believe that either. I believe that many of the disposal wells use INJECTION pumps, some of which are positive displacement, and often use a high pressure to get the fluid downhole as fast as possible.
It seems you are leading up to your simple answer being that it is just Dog at work, increasing seismic activity by a statistically significant amount within short distances of disposal wells. Or maybe you are blaming Obama for starting to screw things up as soon as he got in office.
Sorry, don't buy those either.
So go ahead and tell us poor illiterate souls just what your simple answer really is.

[ROCKMAN]

Hawk – Go back and read what I aid again. First, I didn’t say the formation pressure doesn’t change: I side it changes very slightly…on the order of a few hundred psi. And in the large formations where almost all disposal wells are injecting the pressure doesn’t change just hundreds of feet away from the well. Second, there are SWD wells that pump under pressure. But none of mine do…nor do most of the ones where I’m operating. I know one operator, McGowan and Associates, who is disposing of millions of gallons of salt water per day by gravity drainage. Mr. McGowan is a true legend in the oil patch for his inexpensive salt water disposal efforts: he’s doing around 6,000 bopd from wells that are 98% to 99% water. But, yes, there are also operators pumping down their SWD wells in my area also, including one offsetting one of my leases. And they’re pumping at about 1,200 psi. And you say: “…often use a high pressure”. A meaningless statement until you say what that pressure is. And again let’s not forget if you’re injecting into a reservoir at around 4,500’ the BHP is around 1,800 psi NATUTRALLY without any injection. How do you think you can get the formation to take water if the pressure from the column of water is only equal to 1,800 psi?

As far as buying anything I say that’s not relevant: you don’t have to buy one f*cking word I’ve said. It’s all a matter of the laws of physics. And since I don’t want to waste any more space here trying to educate you here are some links to hydrostatic pressure and SWD wells. You can educate yourself and then come back with proof to show where I’ve said anything that wasn’t factual. Trying to understand subsurface hydrodynamics intuitively just isn’t going to work. It’s a matter of science and engineering. Knowledge that no one is born with. LOL.

http://www2.epa.gov/sites/production/fi ... al_508.pdf
http://www.twdb.texas.gov/publications/ ... 4/R274.pdf
http://www.tceq.state.tx.us/permitting/ ... wells.html

As far as the increased seismic activity being an act of God of course, being a devout atheist, I don’t “buy that” either. LOL. Just as the other hundreds of thousands of similar sized tremors that occur in the US year are also not acts of God. But I’ll ask you (and the other silent folks) the same question again which you are apparently lack the nerve to answer: if those OK disposal wells caused the increase in OK tremor activity only after 2009 then why didn’t the same disposal wells that have been injecting trillions of gallons for decades before 2009 not also cause an increase in tremors? You seem to blow a lot of agitated smoke trying to avoid such a simple question with such an obvious answer. Why not just man up and answer it: everyone else here knows the answer even if they aren’t willing to say so publicly. LOL.

[Hawkcreek]

As far as the increased seismic activity being an act of God of course, being a devout atheist, I don’t “buy that” either. LOL. Just as the other hundreds of thousands of similar sized tremors that occur in the US year are also not acts of God. But I’ll ask you (and the other silent folks) the same question again which you are apparently lack the nerve to answer: if those OK disposal wells caused the increase in OK tremor activity only after 2009 then why didn’t the same disposal wells that have been injecting trillions of gallons for decades before 2009 not also cause an increase in tremors? You seem to blow a lot of agitated smoke trying to avoid such a simple question with such an obvious answer. Why not just man up and answer it: everyone else here knows the answer even if they aren’t willing to say so publicly. LOL.

Ok, I confess. I don't know the obvious answer to the question you seem unwilling to give an answer to. You keep saying "everyone" knows the answer. I don't, so teach me. It couldn't be that you would rather not give your opinion out in the open for others to shoot at?
If you are saying that the disposal wells did not cause the tremors in the areas around them, you seem to be saying that statistical significance does not mean anything. The tool used most often in research and science means nothing?
So, what causes the tremors? Out with it. Teach us, oh great one.
I forgot, you do not have time to educate me. So consider this just stating the obvious, so that "everyone" can confirm what they already know.

[Hawkcreek]

BTW - the links you included don't confirm your opinion in the least. Two of them were just fluff pieces trying to tell the public that nothing bad can happen from injecting crap into the ground. None of them give downhole pressure profiles (top to bottom).

[Synapsid]

ROCKMAN,

OK (snif), I went and looked.

Oklahoma does indeed forbid drillers of disposal wells from drilling into basement, and requires operators to show that they aren't doing so, from drill logs or gamma survey. If an operator doesn't do that he/she/it can be shut down.

The reason given is that drilling into basement could increase earthquake hazard, meaning big quakes, not the kind in the news in Oklahoma currently.

And the reason for THAT is that the preferred units to use for SWD comprise the Arbuckle Group, which I suspect you're familiar with, and the Arbuckle (mostly dolomite from the strat column I looked at) underlies most of the state and is only separated from basement rock by the Lamotte Sandstone--the Arbuckle, in other words, is almost basal.

The icing on the cake is that the director of the Oklahoma Geological Survey was in grad school with me. He was often addressed as Cap'n Phaser. He's a sharp guy.

[Synapsid]

Correction to my post:

The Lamotte is included in the Arbuckle sensu lato.

[shallow sand]

New to this discussion, but correct me if I am wrong.

The increase in seismic activity has occurred since the proliferation of horizontal drilling and high volume multi stage frack jobs.

It seems I have read that several new, very deep disposal wells were drilled to handle this water, with large volumes being disposed of at high pressure.

We primarily inject water into the producing zone. We do have a few water supply wells which are adding water to the producing formation. However, mostly we are just recycling water, hoping it sweeps a little oil along the way.

The disposal of water/water flooding has occurred here since around WW2. Problem here to worry about is not seismic activity, but casing holes.

What are the rates/pressures of these "offending" SWD wells?

[ROCKMAN]

Syn - Good info but I think you're still missing the obvious. Do you have a granite counter top by any chance? But I'm sure you've seen them. Exactly how would you inject fluid into an igneous rock? A rock that has no capability of being injected into. Remember you have to be injecting into a rock that has pore space into which the fluid could be pushed. There is ZERO PORE SPACE in any igneous basement rock. Thus the point I made about the lack of any need to make such rules. Basement rock is basement rock...it is not the Arbuckle.

shallow: read the article again: they are not correlating increased tremor activity with frac'ng or hz wells. They VERY CLEARLY state they are just looking at salt water disposal wells. But don't believe anything I say. read this report which actually includes support for some of the points I've made FROM THE WRITTERS OF THE REPORT ITSELF:

Five Things to Know About a New Stanford Oklahoma Earthquake Study by Seth Whitehead

Today, Stanford University geophysicists F. Rall Walsh III and Mark Zoback released a new study in the journal Science Advances entitled, “Oklahoma’s Recent Earthquakes and Saltwater Disposal.” The researchers claim the increase in seismic activity has coincided with a dramatic increase in volumes of disposal of salty wastewater into the Arbuckle formation, a 7,000 foot deep, sedimentary formation under Oklahoma. They believe formation is in hydraulic communication with the crystalline basement, where almost all of the earthquakes are occurring. Everyone can agree that no matter what is causing the spike of seismic activity in Oklahoma over the past five years, it’s an issue that all parties want to see addressed. While this study is certainly a significant contribution to scientific knowledge – and much of the data and analysis provided will help us better understand induced seismicity in Oklahoma – the researchers’ focus on wastewater volumes and comparative lack of downhole pressure analysis (among other factors) does raise a number of questions to consider.

Here are five key facts to know while reviewing this new report:

Fact #1 - Produced water volumes much higher in the 1980s, yet there was minimal seismic activity. Walsh et al. suggest an increase in injected volumes in recent years is the determining factor for Oklahoma’s increased seismicity. But the reserachers’ data only go as far back as 1997. As the chart below shows (using preliminary data provided by the Oklahoma Geological Survey), produced water volumes were roughly 30 percent higher in Oklahoma during the 1980s than they were in 2011, yet there was minimal seismic activity at the time. Compare this data going back to the 1980s with the data in the Stanford study, which only goes back to 1997. As the report explains, “As can be seen in figure 2, the aggregate monthly injection volume in the state gradually double from about 80 million barrels/month in 1997 to about 160 million barrels/month in 2013.” But it does not include

{And just in case anyone missed it: “…using preliminary data provided by the Oklahoma Geological Survey), produced water volumes were roughly 30 percent higher in Oklahoma during the 1980s than they were in 2011, yet there was minimal seismic activity at the time. …the fact that volumes were about 30 percent higher in the 1980s.”}

Oklahoma Quakes - Of course, the researchers focus specifically on the increases in wastewater injection in the Arbuckle formation to come to their conclusions. Their data certainly show an increase in disposal volumes coinciding with an increase in seismicity. However, in order to gain a thorough picture as to whether the volumes themselves are the cause of the seismicity, the data would need to stretch back to the 1980s to determine if injection into disposal wells was also higher in the Arbuckle formation, as it was across the entire state. While we know that wastewater injection was certainly taking place in the Arbuckle formation in the 1980s, neither the OGS data nor the Stanford researchers’ data for the Arbuckle go back far enough determine if there was an increase or decrease. But with actual volumes of wastewater throughout the state being so much higher in the 1980s, understanding how much was going into Arbuckle at that time is an important part of the puzzle, which is not addressed in the study.

Fact #2 - Researchers focus almost entirely on volume as the trigger for seismicity while glossing over other well-established factors. The press release states, “Stanford geophysicists have identified the triggering mechanism responsible for the recent spike of earthquakes in parts of Oklahoma-a crucial first step in eventually stopping them. In a new study published in the June 19 issue of the journal Science Advances, Professor Mark Zoback and PhD student Rall Walsh show that the state’s rising number of earthquakes coincided with dramatic increases the disposal of salty wastewater into the Arbuckle formation, a 7,000-foot-deep, sedimentary formation under Oklahoma.”

In other words, the researchers claim to have identified the triggering mechanism for seismicity: high volume injection. But it’s important to note Southwestern Oklahoma has high injection volumes but few if any felt seismic events. The same can be said for western and northeast Oklahoma. It’s long been established that one factor alone cannot be blamed solely for seismicity. As the USGS recently explained, “A combination of many factors is necessary for injection to induce felt earthquakes. These include the injection rate and total volume injected; the presence of faults that are large enough to produce felt earthquakes; stresses that are large enough to produce earthquakes; and the presence of pathways for the fluid pressure to travel from the injection point to faults.” The EPA has come to a similar conclusion: “The three key components behind injection-induced seismicity are (1) sufficient pressure buildup from disposal activities, (2) a Fault of Concern, and (3) a pathway allowing the increased pressure to communicate from the disposal well to the fault. All three components must be present to induce seismicity.”

{And again let’s not miss an important FACT: “But it’s important to note Southwestern Oklahoma has high injection volumes but few if any felt seismic events. The same can be said for western and northeast Oklahoma.”

As a recent compendium of seismicity reports conducted by the Southern Methodist University warns, “The potential for seismic activity must be addressed based on downhole pressure, injected volumes, and location, including the orientation of certain faults. Peer-reviewed studies have consistently identified these variables as necessary to understand induced seismicity, and not to convey a blanket, one-size-fits-all approach that suggests geological or pressure conditions in any given area are analogous to operations in other parts of the country.” That’s also precisely why effectively addressing induced seismicity from injection wells requires a site by site approach, taking into account the fact that geological conditions are not uniform and similar wells in different areas may or may not have any nearby seismicity.

{And with respect to that map with all those little red dots pointing out tremors: “Also important is that 80 percent of Oklahoma is within nine miles of an injection well, yet 80 percent of the state is not experiencing induced seismicity. On that point, the researchers do admit”. So to be very clear: 80% of OK has disposal well in the immediate proximity and yet 80% of the state has not seen an increase in tremors.}

“With thousands of injection wells in the state, it is likely that some naturally-occurring earthquakes would occur in the vicinity of disposal wells.” In other words, a blanket, one size fits all approach is not an appropriate solution since every well is operating in different geologies and conditions.

{Which is apparently the point I’ve been unable to make various closed minded individuals understand}

Fact #3 - Fracking not to blame - Walsh et al.’s report makes it crystal clear that the fracking process is not to blame for the spike in seismicity in Oklahoma. Zoback had the following to say in press release accompanying the report: “What we’ve learned in this study is that the fluid injection responsible for most of the recent quakes in Oklahoma is due to production and subsequent injection of massive amounts of wastewater, and is unrelated to hydraulic fracturing.” (emphasis added). Fracking isn’t even discussed at length until the sixth page of the report, and the report points out that fracking fluids are a very small component of wastewater disposal: “… hydraulic fracturing flow back water comprises an extremely small fraction of the injection into the SWD (salt water disposal) wells… In other words, nearly all the water being injected into SWD wells in these areas is produced water.”

{And one more time: “…fracking fluids are a very small component of wastewater disposal”

Interestingly, much of the wastewater in central Oklahoma has nothing to do with hydraulic fracturing at all – a fact alluded to in the press release accompanying their report: “Because the pair were also able to review data about the total amount of wastewater injected at wells, as well as the total amount of hydraulic fracturing happening in each study area, they were able to conclude that the bulk of the injected water was produced water generated using conventional oil extraction techniques, not during hydraulic fracturing.”

A recent lead story in Seismological Research Letters talked on this underreported fact as well. “Salt water is produced at virtually all oil wells, whether the wells were hydraulically fractured or not. In fact, hydraulic fracturing is not used in the Hunton Dewatering Play in central Oklahoma, yet it is one of the largest producers of salt water in the United States.”

The USGS recently made similar comments. “… In some parts of Oklahoma where very high volumes of wastewater are injected, no hydraulic fracturing is occurring at all, so the wastewater is purely saltwater that comes up with oil in the extraction process.”

Some media outlets have perpetuated the myth that there would be no need for wastewater disposal if hydraulic fracturing was not used. But the fact is that wastewater is produced in nearly every oil and gas well, not just wells that have been fracked. No wonder Zoback recently had the following comment in the Dallas Morning News: “I really think bans on hydraulic fracturing are political statements rather than risk management tools.”

{And again from the guy that wrote the f*cking report: “I really think bans on hydraulic fracturing are political statements rather than risk management tools.” LOL. And thus my castigation of those who tried to hijack this thread into a discussion of the dangers of frac’ng.}

Fact #4 - More than 99 percent of injection wells operate without seismicity: With the focus of the report being on volumes injected, the researchers did not address the very important issue of how many injection wells could be linked to seismicity. Numerous experts have found that out of the tens of thousands of wells operating across the United States, only a fraction of them have been linked to seismic activity. As the USGS explained just a few weeks ago, “Most injection wells do not trigger felt earthquakes.” As the USGS has pointed out previously: “Of more than 150,000 Class II injection wells in the United States, roughly 40,000 are waste fluid disposal wells for oil and gas operations. Only a small fraction of these disposal wells have induced earthquakes that are large enough to be of concern to the public.”

The National Research Council – part of the prestigious National Academies – has concluded: “Injection for disposal of wastewater derived from energy technologies into the subsurface does pose some risk for induced seismicity, but very few events have been documented over the past several decades relative to the large number of disposal wells in operation.” A study released last summer in Science magazine concluded that just four injection wells could be responsible for 20 percent of the earthquakes, not just in Oklahoma, but throughout the entire central United States. A major report recently released by the U.S. Environmental Protection Agency, which was intended to help clarify induced seismicity for the purpose of better managing risks, concluded that “very few” of the tens of thousands of disposal wells in the United States have produced any notable seismic activity.

Energy In Depth released an analysis of North Texas earthquakes, which looks at data from the Texas Railroad Commission of Texas as well as a number of recent peer reviewed studies and finds that only one-tenth of one-percent of injection wells across the Barnett Shale – or fewer than two dozen of them – have any sort of plausible connection to earthquakes.

Fact #5 - Industry, scientists and regulators are collaborating to manage the risk: Like most recent reputable studies, Walsh et al. calls for increased collaboration between industry, scientists, and regulators, and that’s exactly what has been happening in recent years. In Oklahoma, the Corporation Commission (OCC) has increased its scrutiny for new injection wells in seismically active areas and strengthened its oversight. The onus is now on producers to prove they’re not injecting into fault-riddled bedrock. The state also works under a “traffic light system,” recommended by the National Academy of Sciences. Under that system, no injection wells are permitted in “red-light” zones, or areas where seismicity is actively occurring. Wells with a “yellow-light” status are more closely monitored, which means the state can even shut them down if their operation leads to seismicity. As many as 20 permit apps for injection wells in Oklahoma were never filed because they were in red-light zones and 25 app permits were rejected.

State First has also created an induced seismicity working group, which brings together state regulatory agencies and geological surveys, along with the Ground Water Protection Council, to share science and research. In these collaborative efforts, fault data and other geological information are shared with the state geological survey, the Corporation Commission, and research institutions such as Stanford (this study), the University of Oklahoma, and Southern Methodist University (among others). The industry has also helped to secure funding for additional seismic monitoring throughout Oklahoma. Oklahoma currently has 20 permanent seismic monitors and 15 temporary monitors, which means the state has one of the most robust seismic monitoring systems in the U.S. OGS seismologist Amberlee Darold explained that industry has in-depth information on the thousands of faults in Oklahoma that have proved invaluable: “They are giving us their proprietary information to help the state as a whole understand the faults.”

OCC Oil and Gas Conservation Division Director Tim Baker said industry has been cooperative and has recognized the risks associated with injecting in elevated-risk, basement rock areas. Steps have already been taken to address disposal in the Arbuckle group. In March 2014, the OCC voted unanimously to adopt new rules requiring additional data monitoring and reporting of pressure for disposal wells in the Arbuckle formation and those rules went into effect in September. Pressure and volumes in Arbuckle formation “Areas of Interest” must now be recorded daily and reported weekly to the OCC. The new rules also subject wells injecting 20,000 or more barrels a day to be subject to mechanical integrity tests and all injection applications must undergo seismic review. The “Area of Interest” applies to 347 of 900 Arbuckle injection wells.

{I gather the key word in there is “funding”: looks like Stanford and Dr. Walsh will see a few grants heading their way.}

[Synapsid]

ROCKMAN,

Now, now: I'm not saying anything about injection wells into basement rock. The State of Oklahoma is, and says that you are not allowed to drill such, owing to earthquake hazard.

My first post suggested that hazard related to activating faults in the New Madrid zone might be behind Oklahoma forbidding drilling into basement for injection wells; I seemed to remember reading that that was the case, and indeed it is. It's their idea, not mine, and I'd guess that the concern arises from the chance of basement rock (is it igneous there? It's Precambrian but I don't know what kind of rock) being fractured and thus allowing fluid movement. Rock in a fault zone is going to be fractured, after all, and the New Madrid zone is a big one.

It sounds like they're being careful.

[Hawkcreek]

Ok, this makes it clear to me -- the quakes in Oklahoma are caused either by oil production, or disposal of oil production fluids.
You were right Rock. Lots of words, simple answer. Thanks for pointing it out.

[Apneaman]

Oklahoma cracks down more on disposal wells after Cushing quakes

Date: 21-Oct-15
Country: USA
Author: Liz Hampton in Houston and Heide Brandes in Cushing;
Oklahoma regulators are cracking down harder on saltwater disposal wells near the vitally important Cushing crude storage hub, where a rash of quakes have stoked concerns its tanks and pipelines may not be designed to handle a major seismic event.

The state's oil and gas regulator late on Monday said all saltwater disposal wells within a 10-mile radius of Cushing could face new limits. It has also basically halted approvals for new disposal wells for the time being and ordered 13 wells to shut in or reduce the amount of water they inject deep into the earth.

Once considered an area of "moderate seismic risk", Oklahoma now experiences as many as two magnitude 3.0 or higher earthquakes a day, up from just two a year in 2008. The uptick has been attributed to the disposal of saltwater, a normal byproduct of oil drilling, into deep wells.

In September, in a bid to curb the frequency of the quakes, the Oklahoma Corporation Commission (OCC), which regulates the state's oil industry, ordered drilling companies to shut or reduce usage at half a dozen saltwater wells near Cushing. Just one month later, a pair of earthquakes registering at 4.4 and 4.5 struck near Cushing, renewing safety concerns among residents and regulators alike.

While the OCC is not currently issuing new permits for disposal wells near Cushing, there are still an estimated 3,500 wells operating in the state. These play an important role servicing the oil and gas industry that has long been key to the economy of the Sooner State.

But shutting these wells has the potential to quell the tectonic disruption in Oklahoma, scientists interviewed by Reuters said.

"In most cases the seismicity would decrease at some rate and eventually it would go away. Sometimes it can take only weeks to a month, but there are always weird cases where it may take longer," Egill Hauksson, a geophysics professor at California Institute of Technology, said.

The largest earthquake to strike Oklahoma was in 2011, 40 miles from Cushing near Prague, Oklahoma. It was a 5.6, strong enough to cause potential damage to oil infrastructure.

Some of the 7,889 residents in the town of Cushing say this is a concern as the hub is home to an estimated 54 million barrels of stored oil and the delivery point for the widely traded West Texas Intermediate (WTI) futures contract.

(Editing by Terry Wade and Chizu Nomiyama)

Reuters
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http://planetark.org/wen/73788