[Zarquon]

When I first heard about "fracking causes earthquakes" a few years ago, I put it in the same category as burning tapwater and forgot it. Apparently I was wrong: it's wastewater disposal, not fracking, and it's now officially a fact in Oklahoma, but not in Texas:

http://www.scientificamerican.com/artic ... rthquakes/

"To many Oklahomans, it is clear that that risk has risen sharply. Data backs up their experiences. The earthquake rate in the state has grown at an astounding pace. In 2013 the state recorded 109 quakes of magnitude 3 and greater. The following year the number jumped to 585, and in 2015 it reached 890.

The escalation prompted two unusual warnings jointly issued by the USGS and the OGS in October 2013 and May 2014. Seismologists stated that Oklahoma had a significantly increased chance of seeing a damaging magnitude 5.5 temblor. “It was the first time I think we’d ever issued an earthquake advisory east of the Rockies,” says Robert Williams, the USGS central and eastern U.S. coordinator for earthquake hazards."

[Subjectivist]

It is an interesting article thanks for posting the link. A couple points raised by the author, the USGS has known how fast you could pump fluids into a well without serious earthquake impact since the 1960's, but for various reasons this knowledge was not properly applied to the 21st century.

Second point, and this is significant to me. The induced earthquakes are in already existing fault structures that are under stress. These faults will continue building energy until they break and release that energy. The fluid injections are in effect allowing the faults to slip more easily at lower energy than they would naturally break at. Done in a calculated manner it is possible that deliberate injection schedules could be designed to creat thousands of small quakes that would release the energy safely over a period of a few years instead of suddenly all in one big earthquake.

[rockdoc123]

The fluid injections are in effect allowing the faults to slip more easily at lower energy than they would naturally break at. Done in a calculated manner it is possible that deliberate injection schedules could be designed to creat thousands of small quakes that would release the energy safely over a period of a few years instead of suddenly all in one big earthquake.

Exactly. A few times I've mentioned the work done in the seventies by various groups (Centre for Tectonophysics, Caltech etc) who were researching earthquakes with the San Andreas system as its outdoor laboratory. The recommendations from back then were that water should be pumped down wells to create small continuous fault displacements along the Garlock and several other faults that link into the San Andreas. As you mention the large earthquakes occur due to stress accumulation and sudden release under stick-slip conditions.

My guess as to why pump rates haven't been legislated is cost considerations. The state needs activity to collect royalties and increasing costs to companies through regulations might decrease the amount of drilling based on economic considerations (i.e. you have to get rid of a certain amount of water each day so without huge storage you would need more disposal wells if your pump rates were lower). I suspect another issue is that the USGS hasn't done a detailed enough study of the existing fault and fracture network. More specifically they likely haven't done much in the way of geomechanics with a mind to understanding in situ stresses and strains that impact which faults might or might not be reacitivated.

[Zarquon]

I found this FAQ at the USGD:
https://www2.usgs.gov/faq/categories/9833/3424

"Do all wastewater disposal wells induce earthquakes?

No. 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."

I didn't know there are so many disposal wells in the US (OK, until very recently I didn't know they exist at all). Seems you have to have to hit the right spot to induce tremors, but until very recently nobody knew this (or gave a damn). But it takes years (?) before the water has traveled far enough for the effects to become apparent, and by then the fractures have already been greased and the horse has left the barn. Is that it? And would it be prohibitively expensive or difficult to identify locations for new wells that are safe?

edit: I just realized your last post already answered that.

[rockdoc123]

I didn't know there are so many disposal wells in the US (OK, until very recently I didn't know they exist at all). Seems you have to have to hit the right spot to induce tremors, but until very recently nobody knew this (or gave a damn). But it takes years (?) before the water has traveled far enough for the effects to become apparent, and by then the fractures have already been greased and the horse has left the barn. Is that it? And would it be prohibitively expensive or difficult to identify locations for new wells that are safe?

The requirements for waste disposal water to create an earthquake are 1. pre-existing faults 2. insitu stress and strain that is in the correct orientation for high pore fluid pressure to effectively reactivate the fault 3. high enough pore fluid pressure from pumping that a fault in the correct orientation can be reactivated. It doesn't take years, it can occur immediately or it may take longer depending on what the actual amount of stress from pore fluid pressure that is required to reactivate the fault. If the required stress is low the fault might occur almost immediately it the stress is high it may take sometime for pore fluid pressure to build up.

As I said in my previous note a certain amount of geomechanics analysis is required (understanding in-situ stresses and strains). This information can be obtained from new wells when they are drilled and can be also estimated from 3 D sesimic by analysis of wavelet properties. The sesimic is also necessary to map out existing faults. In shale exploration companies will go through these hoops prior to planning a fracking program simply because they want to stay away from existing faults.