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Permalink Reply by Dion Warr, CPL on August 14, 2009 at 4:00

E & E:

This explanation seems plausible. As I understand it, SWD injection into a fault changes the pressure and friction characteristics along the fault line (ie., injection volume and pressure can hold fault blocks slightly further apart, and fluid flow allows for more slip along the fault line(s).)

I'd be interested as to what Les B thinks about this story.

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Permalink Reply by Mac Davis on August 14, 2009 at 4:46

Wouldn't saltwater disposal wells involve a larger volume of water spread over a larger area of land than fracking? Would you try to dispose of salt water into a low permeability formation like the Haynesville Shale?

It seems that fracking would be a small, intense stimulus, and saltwater disposal would be less intense, but spread over a much larger area.

My other thought is that small quakes may be a good thing. Release the stress slowly instead of all at once. 1000 magnitude 3 earthquakes will probably do a lot less damage than one magnitude 5, but it's the same amount of energy. It seems that the energy involved in even a tiny quake would come from the geological stresses already in the rock being prematurely released by the water, rather than from the energy used to pump the water underground. Releasing this stress a bit at a time may be beneficial.

Does anyone know how much pressure and volume of water is used in salt water disposal well vs. fracking a well?

More info:

http://www.bloomberg.com/apps/news?pid=20601103&sid=a1CqcpRp2jW8

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Permalink Reply by Dion Warr, CPL on August 19, 2009 at 13:02

Mac:

Therein lies the problem. Injecting into the SWD also fills depleted and/or porous formations with added mass, and if wedged against more impervious barriers, the mass shift and lessened friction tends to cause quick slips rather than slow plodding movements.

I'll notate below, but the Star-Telegram actually corrected the SWD total to 2.8 million barrels of injected material, instead of billion (which would be some kind of record or something). Still, loading a billion pounds of material into one side of a fault block over less than one years time, one would expect some sort of 'adjustment'.

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Permalink Reply by The_Baron on August 20, 2009 at 4:24

It should be noted that in fracking the water is injected rapidly over short time. In a SWD, disposal takes place at a rather consitant rate over long periods of time. While I do not have the appropriate geologic background to comment on Dions statements about fault loading, they seem plausible to me.

Also, while I can not speak for the Barnett, the SWDs I have been involved with typically inject into very porous sands. The injection pressures are typically very low.

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Permalink Reply by jffree1 on August 14, 2009 at 8:49

Here's an excerpt from the Star-Telegram story about the two disposal wells:

http://www.star-telegram.com/state_news/story/1537502.html

The airport well was drilled to 13,780 feet, twice the depth of some gas wells, and completed in August, Frohlich said. It also was drilled about 2,400 feet from a major fault running through the airport, said Julie Wilson, a spokeswoman for Oklahoma City-based Chesapeake.

Cautionary Move

"Preliminary results have indicated there is no correlation between natural-gas drilling and fracturing activities and the minor earthquakes that have occurred over the last several months in North Texas," Wilson said.

Chesapeake stopped using the airport saltwater disposal well and another at Cleburne, where numerous tremors have been reported, as a precaution, she said. The action did not affect gas production.

Chesapeake pumped 2.8 billion barrels of water into the airport well from Sept. 12, 2008, until it was shut after the company met with geologists June 29, Steven Turk, vice president of the company’s southern operations, said in an interview.

"We really had no reason to believe we would ever have a problem such as it appears we've ended up with, where injecting into the Ellenberger near one of these big faults would in any way trigger these small earthquakes," said Larry Lunardi, Chesapeake vice president for geoscience. The Ellenberger is a porous layer of rock 2 miles deep.

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Permalink Reply by Dion Warr, CPL on August 19, 2009 at 13:04

Jffree1:

Noted above, but the Star-Telegram corrected the injection total to 2.8 million barrels of injected material, instead of billion.

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Permalink Reply by jffree1 on August 19, 2009 at 13:22

Thanks, Dion. I had not seen the update but will look for it now.

It occurs to me that maybe the operators would prefer to have attention directed toward a couple of disposal wells rather than "fracking" as the culprit behind the seismic activity in North Texas... and it does appear to be a reasonable explanation. But then IANAG.

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Permalink Reply by Stevew on August 19, 2009 at 14:35

Geez Guys .... don't I have enough to worry about?

.... forest fires, drought, low NG prices and health care.

I don't need earthquakes.

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Permalink Reply by Rosebud on August 20, 2009 at 11:55

I was talking to someone in the Northeast about the Haynesville Shale, forgetting at the moment about the Marcellus Shale, and the first comment this person made was they'd maybe had some minor earthquakes believed to be related to the drilling process.

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