Hydraulic Fracture Drilling-Part 7

Increased Seismicity due to injection wells





Within the central and eastern United States, the number of earthquakes has increased dramatically over the past few years. Between the years 1973–2008, there was an average of 21 earthquakes of magnitude three and larger in the central and eastern United States. This rate jumped to an average of 99 M3+ earthquakes per year in 2009–2013, and the rate continues to rise. In 2014, alone, there were 659 M3 and larger earthquakes . Most of these earthquakes are in the magnitude 3–4 range, large enough to have been felt by many people, yet small enough to rarely cause damage. There were reports of damage from some of the larger events, including the M5.6 Prague, Oklahoma earthquake and the M5.3 Trinidad, Colorado earthquake.
This increase in earthquakes prompts two important questions:

• Are they natural, or man-made?
• What should be done in the future as we address the causes and consequences of these events to reduce associated risks?

Preliminary Findings

Cumulative number of earthquakes with a magnitude of 3.0 or larger in the central and eastern United States, 1970–2014. The dashed line corresponds to the long-term rate of 29 earthquakes per year, with an increase in the rate of earthquakes starting around 2009.

A team of USGS scientists led by Bill Ellsworth analyzed changes in the rate of earthquake occurrence using large USGS databases of earthquakes recorded since 1970. The increase in seismicity has been found to coincide with the injection of wastewater in deep disposal wells in several locations, including Colorado, Texas, Arkansas, Oklahoma and Ohio. Much of this wastewater is a byproduct of oil and gas production and is routinely disposed of by injection into wells specifically designed and approved for this purpose.
Hydraulic fracturing, commonly known as “fracking,” does not appear to be linked to the increased rate of magnitude 3 and larger earthquakes.
Although wastewater injection has not yet been linked to large earthquakes (M6+), scientists cannot eliminate the possibility. It does appear that wastewater disposal induced the M5.3 Raton Basin, Colorado earthquake in 2011 as well as the M5.6 quake that struck Prague, Oklahoma in 2011, leading to a few injuries and damage to more than a dozen homes.



 Exert from "Decoded=Science"
 

It goes without saying that an earthquake is a natural phenomenon, caused when movement occurs along a fault in the earth’s crust. This movement is usually the result of major earth forces of compression and extension. But there’s also a phenomenon known as induced seismicity, whereby human activity alters the stresses on a fault and causes it to reactivate.
In fracking, the use of water is the key to inducing earthquakes – increased water injection increases pore pressure in the rock and effectively weakens it. Such an impact is more significant at deeper levels where the rock is stronger and can accumulate greater amounts of strain before it breaks.

Well heads hooked up in preparation for a hydraulic fracturing operation at a drill pad in the Fayetteville Shale gas play of Arkansas. Image credit: Bill Cunningham, USGS

According to the British Geological Survey’s Brian Baptie, with induced earthquakes – just as in natural ones – the risk of a tremor is higher in areas where the rock is already weakened. “In fracture and fault zones the water lubricates the faults and brings them closer to failure, which is what happened in Blackpool,” he explained. “The incidence of earthquakes depends on structure rather than rock type.”

“The fracking process involves two different elements,” explained Dr Baptie. “There’s fracking itself, where the water is pumped into the rock at relatively shallow levels and then out again. And there’s the disposal of contaminated wastewater, when it’s pumped into the rock at a deeper level (usually around 2.5km). Most of the fracking-related earthquakes come from this second stage.”

How Big Can an Induced Earthquake Be?

The magnitude of an earthquake depends on the strength of the rock. The biggest earthquake in recorded history is the magnitude 9.5 (M9.5) earthquake which struck off Chile in 1960. Like most other major earthquakes, this occurred at a subduction zone and was entirely natural.

Induced earthquakes, though they may be significant in their local tectonic context, do not compare with these ‘megathrust’ earthquakes, where massive strain builds up over enormous distances along faults fault.

In Oklahoma, the largest tremor in the state was the M5.6 which struck Prague in 2011. Although this seismic event may not have been directly fracking-induced, the USGS notes that research “suggests that a magnitude 5.0 foreshock to the 2011 Prague, Okla., earthquake was human-induced by fluid injection; that earthquake may have then triggered the mainshock and its aftershocks.”

Most earthquakes we know to be fracking-induced are smaller than this, however.
To place this in context, it’s important to remember than the earthquake magnitude scale is logarithmic – an earthquake of M5 is ten times bigger than an M4 and one hundred times the size of an M3 and so on. This means that the magnitude difference of 3.5 between Oklahoma in 2011 and Chile in 1960 actually represents a difference in size of almost 8000 times – and in terms of energy released, the Chile ‘quake was a mind-boggling 707,000 time larger than the Oklahoma tremor.

 

 

Study raises new concern about earthquakes and fracking fluids

 

 

NEW YORK | By Sharon Begley 

 

NEW YORK Powerful earthquakes thousands of miles away can trigger swarms of minor quakes near wastewater-injection wells like those used in oil and gas recovery, scientists reported on Thursday, sometimes followed months later by quakes big enough to destroy buildings.

 

The discovery, published in the journal Science by one of the world's leading seismology labs, threatens to make hydraulic fracturing, or "fracking," which involves injecting fluid deep underground, even more controversial.

 

It comes as the U.S. Environmental Protection Agency conducts a study of the effects of fracking, particularly the disposal of wastewater, which could form the basis of new regulations on oil and gas drilling.

 

Geologists have known for 50 years that injecting fluid underground can increase pressure on seismic faults and make them more likely to slip. The result is an "induced" quake.

A recent surge in U.S. oil and gas production - much of it using vast amounts of water to crack open rocks and release natural gas, as in fracking, or to bring up oil and gas from standard wells - has been linked to an increase in small to moderate induced earthquakes in Oklahoma, Arkansas, Ohio, Texas and Colorado.

 

Now seismologists at Columbia University say they have identified three quakes - in Oklahoma, Colorado and Texas - that were triggered at injection-well sites by major earthquakes a long distance away.

 

"The fluids (in wastewater injection wells) are driving the faults to their tipping point," said Nicholas van der Elst of Columbia's Lamont-Doherty Earth Observatory in Palisades, New York, who led the study. It was funded by the National Science Foundation and the U.S. Geological Survey.

 

Fracking opponents' main concern is that it will release toxic chemicals into water supplies, said John Armstrong, a spokesman for New Yorkers Against Fracking, an advocacy group.

But "when you tell people the process is linked to earthquakes, the reaction is, 'what? They're doing something that can cause earthquakes?' This really should be a stark warning," he said.

 

Fracking proponents reacted cautiously to the study.

"More fact-based research ... aimed at further reducing the very rare occurrence of seismicity associated with underground injection wells is welcomed, and will certainly help enable more responsible natural gas development," said Kathryn Klaber, chief executive of the Marcellus Shale Coalition.

 

'DYNAMIC TRIGGERING'

 

Quakes with a magnitude of 2 or lower, which can hardly be felt, are routinely produced in fracking, said geologist William Ellsworth of the U.S. Geological Survey, an expert on human-induced earthquakes who was not involved in the study.

The largest fracking-induced earthquake "was magnitude 3.6, which is too small to pose a serious risk," he wrote in Science.

 

But van der Elst and colleagues found evidence that injection wells can set the stage for more dangerous quakes. Because pressure from wastewater wells stresses nearby faults, if seismic waves speeding across Earth's surface hit the fault it can rupture and, months later, produce an earthquake stronger than magnitude 5.

 

What seems to happen is that wastewater injection leaves local faults "critically loaded," or on the verge of rupture. Even weak seismic waves from faraway quakes are therefore enough to set off a swarm of small quakes in a process called "dynamic triggering."

"I have observed remote triggering in Oklahoma," said seismologist Austin Holland of the Oklahoma Geological Survey, who was not involved in the study. "This has occurred in areas where no injections are going on, but it is more likely to occur in injection areas."

Once these triggered quakes stop, the danger is not necessarily over. The swarm of quakes, said Heather Savage of Lamont-Doherty and a co-author of the study, "could indicate that faults are becoming critically stressed and might soon host a larger earthquake."

 

For instance, seismic waves from an 8.8 quake in Maule, Chile, in February 2010 rippled across the planet and triggered a 4.1 quake in Prague, Oklahoma - site of the Wilzetta oil field - some 16 hours later.

 

That was followed by months of smaller tremors in Oklahoma, and then the largest quake yet associated with wastewater injection, a 5.7 temblor in Prague on November 6, 2011.

That quake destroyed 14 homes, buckled a highway and injured two people.

The Prague quake is "not only one of the largest earthquakes to be associated with wastewater disposal, but also one of the largest linked to a remote triggering event," said van der Elst.

 

The Chile quake also caused a swarm of small temblors in Trinidad, Colorado, near wells where wastewater used to extract methane from coal beds had been injected.

On August 22, 2011, a magnitude 5.3 quake hit Trinidad, damaging dozens of buildings.

The 9.1 earthquake in Japan in March 2011, which caused a devastating tsunami, triggered a swarm of small quakes in Snyder, Texas - site of the Cogdell oil field. That autumn, Snyder experienced a 4.5 quake.

 

The presence of injection wells does not mean an area is doomed to have a swarm of earthquakes as a result of seismic activity half a world away, and a swarm of induced quakes does not necessarily portend a big one.

 

Guy, Arkansas; Jones, Oklahoma; and Youngstown, Ohio, have all experienced moderate induced quakes due to fluid injection from oil or gas drilling. But none has had a quake triggered by a distant temblor.

 

Long-distance triggering is most likely where wastewater wells have been operating for decades and where there is little history of earthquake activity, the researchers write.

"The important thing now is to establish how common this is," said Oklahoma's Holland, referring to remotely triggered quakes. "We don't have a good answer to that question yet."

Before the advent of injection wells, triggered earthquakes were a purely natural phenomenon. A 7.3 quake in California's Mojave Desert in 1992 set off a series of tiny quakes north of Yellowstone National Park in Wyoming, for instance. Now, according to the Science paper, triggered quakes can occur where human activity has weakened faults.

Current federal and state regulations for wastewater disposal wells focus on protecting drinking water sources from contamination, not on earthquake hazards.

Fracking Quakes Shake the Shale Gas Industry

 

Well shutdowns prompted by fracking-induced seismicity may inspire technology tweaks.

• By Peter Fairley  

             

 

Shake maker: The Cuadrilla plant near Blackpool.

Geophysicists are increasingly certain that expanding production of shale gas is responsible for a spate of minor earthquakes that have upset some communities and prompted authorities in Arkansas, Ohio, Oklahoma, and the U.K. to shut down some natural-gas operations. The question now, say the experts, is whether the underground operations causing the trouble should be scaled back or more closely monitored to minimize future quakes—and whether the relatively small quakes may yet have the potential to trigger truly destructive ones.

At least one shale gas producer is already talking change: U.K.-based Cuadrilla Resources, whose first project set off quakes near Blackpool last year.

 

Shale gas operations generate microseismicity in two ways. One is through hydraulic fracturing, or “fracking,” the underground blasts of water, sand, and chemicals used to release the natural gas trapped within shale deposits. Fracking is how Cuadrilla caused a quake that measured 2.3 on the Richter scale last April, according to an analysis by the firm’s geophysical consultants.

Similarly, a fracking operation that injected 2.4 million gallons of fluid into an Oklahoma well over six days last January is a likely cause of the 43 earthquakes that followed, according to a state geologist’s report. The 1.0 to 2.8 magnitude quakes began on the second day of injection, and most were centered within 3.5 kilometers of the well. These small quakes were felt on the surface and disturbed nearby residents, but they caused no structural damage.

A second source of shaking from shale gas operations is common to many oil and gas fields: the subsurface disposal of wastewater and of naturally occurring brines that surface with the desired hydrocarbons. Deep-injection disposal wells were probably behind a string of quakes in Arkansas that began in 2010, as well as more recent tremors around Youngstown, Ohio, that culminated in a magnitude 4.0 shake this New Year’s Eve. “There’s no doubt that those Youngstown earthquakes are directly associated with the disposal well there,” says Arthur McGarr, a geophysicist and induced-seismicity expert with the U.S. Geological Survey.