The weight of water behind a new dam in China, for example, is thought to have induced
a 2008 quake in Sichuan Province that killed 80,000 people. In Australia, a 1989 quake
that killed 13 people was attributed in part to the opposite effect
— the removal of millions of tons of coal during more than two centuries of mining.
Τα τελευταία τρία χρόνια, στην πολιτεία της Οκλαχόμα έχουν σημειωθεί χιλιάδες σεισμικές δονήσεις. Μπορεί οι περισσότερες να είναι μικρού μεγέθους, κάποιες δεν γίνονται καν αισθητές, ωστόσο, το 2011 ένας σεισμός 5,6 βαθμών της κλίμακας Ρίχτερ, ο μεγαλύτερος στην ιστορία της πολιτείας, είχε αναστατώσει τους κατοίκους της, προκαλώντας σοβαρές ζημιές σε σπίτια, αλλά και δύο τραυματισμούς.
Κρατικοί αξιωματούχοι και κάτοιχοι δηλώνουν σήμερα ανήσυχοι για τη συχνότητα των σεισμικών δονήσεων, φοβούμενοι πως ο επόμενος σεισμός μπορεί να είναι ακόμη μεγαλύτερος. ...
Την ώρα που οι θέσεις εργασίας 340.000 κατοίκων της πολιτείας είναι άμεσα εξαρτώμενες από τη βιομηχανία πετρελαίου και αερίου, επιστήμονες συνδέουν τις πρακτικές που χρησιμοποιεί με τη ραγδαία αύξηση των σεισμικών δονήσεων.
Γεωλόγοι εδώ και χρόνια έχουν επισημάνει τη συσχέτιση μεταξύ ανθρώπινης δραστηριότητας για την εκμετάλλευση του υπεδάφους και ενεργοποίησης ρηγμάτων εξαιτίας της αλλαγής στις πιέσεις που ασκούνται υπογείως.
Πιο συγκεκριμένα, για την περίπτωση της Οκλαχόμα, παρατηρήθηκε ότι σε ορισμένα κοιτάσματα υδρογονανθράκων γινόταν επί πολλά χρόνια εισπίεση νερού και άλλων υγρών, για να αυξηθεί η παραγωγή πετρελαίου, πρακτική, η οποία υποβοηθά την ενεργοποίηση κάποιου ρήγματος και τη γένεση σεισμών.
Στο Τέξας μια διαφορετική πρακτική για την εξόρυξη πετρελαίου, που έχει μείνει εγκλωβισμένο σε παλαιότερες εξορύξεις, ενοχοποιείται για την πρόκληση σεισμικών δονήσεων, την ώρα που επιστήμονες ισχυρίζονται πως η ίδια η εξόρυξη πετρελαίου και αερίου μπορεί να έχει ακριβώς τα αντίθετα αποτελέσματα, δηλαδή συχνά μπορεί να μειώσει τις πιέσεις και να περιορίσει τις σεισμικές δονήσεις.
Σημασία, προφανώς, δείχνει να έχει η μέθοδος και τεχνική εξόρυξης, σε συνάρτηση με το είδος του κοιτάσματος, και κυρίως το βάθος του.
- Το 2008 σεισμική δόνηση 7,9 βαθμών (απελευθέρωση ενέργειας ίσης με την ισχύ 500 ατομικών βομβών) στην επαρχία Σιτσουάν της Κίνας είχε προκαλέσει το θάνατο 80.000 ανθρώπων. Για την εξαιρετικά ισχυρή αυτή δόνηση είχε ενοχοποιηθεί το βάρος του νερού σε ένα καινούριο φράγμα στην περιοχή.
- Το 1989 σεισμός στην Αυστραλία, που είχε προκαλέσει το θάνατο 13 ατόμων, είχε προκληθεί από την ακριβώς αντίθετη αιτία: από την εξόρυξη εκατομμυρίων τόνων γαιάνθρακα, μέσα σε δύο αιώνες έντονης μεταλλευτικής δραστηριότητας στην περιοχή.
- Στην Καλιφόρνια, αλλά και την Ελβετία, διάφορες εφαρμογές γεωθερμίας έχουν ενοχοποιηθεί για την πρόκληση σεισμικών δονήσεων.
Πληροφορίες:
Experts Eye Oil and Gas Industry as Quakes Shake Oklahoma, Henry Fountain - The New York Times
Examination of Possibly Induced Seismicity from. Hydraulic Fracturing in the Eola Field, Garvin. County, Ok... by Zangogiannis Nasos
-----------------
Possibly Induced Seismicity from Hydraulic Fracturing
(The following is an excerpt from Fracked In The Barnett Shale, by Dr T.L. Hayden)
A recent (August 2011) investigation, “Examination of Possibly Induced Seismicity from Hydraulic Fracturing in the Eola Field, Garvin County, Oklahoma,” by Austin Holland of the Oklahoma Geological Survey provides detailed examination of seismic activity and waves associated with fracking of a gas well. The earthquakes began on Jan. 17, 2011. There were 43 earthquakes recorded, ranging in magnitude from 1.0 to 2.8 milliDarcies. The majority of them occurred in the first 24 hours after fracking ceased on the Picket Unit B well 4-18. The nearest seismic station to record the events was 35 kilometers away, and the majority of the earthquakes detected were within 3.5 kilometers of the fracked well.
Holland used the previously discussed seven questions of Davis and Frohlich to determine if the earthquakes were induced by fluid injection. Five of the questions had a definite “yes” answer. The following two questions had an answer of unknown. Are these events the first earthquakes of this character in the region? Are changes at the hypocentral locations sufficient to encourage seismicity? Several references are given on possible physical mechanisms – for example, diffusion of pore-pressure intersecting with existing fractures that might induce earthquakes. The evidence appears to favor inducement for these events. Holland, however, does not make a definitive call. He concludes, “The strong correlation in time and space as well as a reasonable fit to a physical model suggests that there is a possibility these earthquakes were induced by hydraulic-fracturing. However, the uncertainties in the data make it impossible to say with a high degree of certainty whether or not these earthquakes were triggered by natural means or by nearby hydraulic-fracturing operation.”
In contrast to Holland’s conclusion, C. Frohlich, C. Haywood, B. Stump and E. Potter, in their paper – “The Dallas-Fort Worth Earthquake Sequence: October 2008 through May 2009” (Bulletin of the Seismological Society of America, vol. 101, 2011) – reported five “yes” answers and two unknown answers to the Davis-Frohlich conditions, yet concluded that the earthquakes were induced by an injection well. At least one important factor was different in the two cases: At the DFW site, there was no historical evidence of any previous earthquakes; the Eola field area had numerous previous earthquakes.
Injection wells are regulated in the U.S. by the Underground Injection Control (UIC) program, which covers all aspects of injection wells from initial site selection to abandonment of the well. The UIC program is contained in the Title 40 Code of Federal Regulation (CFR) parts 146 and 148 and is enforced by the EPA. The section that relates to seismic activity is Rule 40 CFR 146.13, which states that injection pressure shall not initiate new fractures or propagate existing fractures in the injection zone. Also, the injection pressure shall not cause movement of injection or formation fluids into underground sources of drinking water.
UIC issues permits for six classes of injection wells, including Class II for O&G and Class VI for carbon dioxide sequestering wells. Specific pathways for contamination of water sources listed were: faulty wall casing; fluid migrating up annulus outside casing; migration from injection formation through confining formation; vertical migration up improperly abandoned well; lateral migration from injection zone into protected zone; and direct fluid injection into or above the water zone. Basic permit conditions include: adequate casing and cementing, including cement bond logs; max pressure allowed to avoid fracturing; and monitoring requirements. Class VI warnings include possible CO2 damage to the well cement. Mathematical models using numerical solutions to predict time and spatial movement of the plume of CO2 are strongly suggested and parameters should minimally include pressure, permeability, and porosity of the injection and confining formations. Monitoring wells are required to check the model data predictions and then necessary updates for corrections should be made to the model
One of the strongest earthquakes
in the history of Oklahoma hit near the town of Sparks on Saturday
night. At 5.6 in magnitude, it was the bell-ringer of a series of
shakes. What is not clear is where this unusual seismic activity is
coming from. The Oklahoman reported:
BTW: The largest gas producers in Oklahoma are not local boys but some pretty heavy hitters.
Source: Oklahoma Corporation Commission: 2009 Report on Oil and Natural Gas Activity Within the State of Oklahoma (page 124)
==========================A recent (August 2011) investigation, “Examination of Possibly Induced Seismicity from Hydraulic Fracturing in the Eola Field, Garvin County, Oklahoma,” by Austin Holland of the Oklahoma Geological Survey provides detailed examination of seismic activity and waves associated with fracking of a gas well. The earthquakes began on Jan. 17, 2011. There were 43 earthquakes recorded, ranging in magnitude from 1.0 to 2.8 milliDarcies. The majority of them occurred in the first 24 hours after fracking ceased on the Picket Unit B well 4-18. The nearest seismic station to record the events was 35 kilometers away, and the majority of the earthquakes detected were within 3.5 kilometers of the fracked well.
Holland used the previously discussed seven questions of Davis and Frohlich to determine if the earthquakes were induced by fluid injection. Five of the questions had a definite “yes” answer. The following two questions had an answer of unknown. Are these events the first earthquakes of this character in the region? Are changes at the hypocentral locations sufficient to encourage seismicity? Several references are given on possible physical mechanisms – for example, diffusion of pore-pressure intersecting with existing fractures that might induce earthquakes. The evidence appears to favor inducement for these events. Holland, however, does not make a definitive call. He concludes, “The strong correlation in time and space as well as a reasonable fit to a physical model suggests that there is a possibility these earthquakes were induced by hydraulic-fracturing. However, the uncertainties in the data make it impossible to say with a high degree of certainty whether or not these earthquakes were triggered by natural means or by nearby hydraulic-fracturing operation.”
In contrast to Holland’s conclusion, C. Frohlich, C. Haywood, B. Stump and E. Potter, in their paper – “The Dallas-Fort Worth Earthquake Sequence: October 2008 through May 2009” (Bulletin of the Seismological Society of America, vol. 101, 2011) – reported five “yes” answers and two unknown answers to the Davis-Frohlich conditions, yet concluded that the earthquakes were induced by an injection well. At least one important factor was different in the two cases: At the DFW site, there was no historical evidence of any previous earthquakes; the Eola field area had numerous previous earthquakes.
Injection wells are regulated in the U.S. by the Underground Injection Control (UIC) program, which covers all aspects of injection wells from initial site selection to abandonment of the well. The UIC program is contained in the Title 40 Code of Federal Regulation (CFR) parts 146 and 148 and is enforced by the EPA. The section that relates to seismic activity is Rule 40 CFR 146.13, which states that injection pressure shall not initiate new fractures or propagate existing fractures in the injection zone. Also, the injection pressure shall not cause movement of injection or formation fluids into underground sources of drinking water.
UIC issues permits for six classes of injection wells, including Class II for O&G and Class VI for carbon dioxide sequestering wells. Specific pathways for contamination of water sources listed were: faulty wall casing; fluid migrating up annulus outside casing; migration from injection formation through confining formation; vertical migration up improperly abandoned well; lateral migration from injection zone into protected zone; and direct fluid injection into or above the water zone. Basic permit conditions include: adequate casing and cementing, including cement bond logs; max pressure allowed to avoid fracturing; and monitoring requirements. Class VI warnings include possible CO2 damage to the well cement. Mathematical models using numerical solutions to predict time and spatial movement of the plume of CO2 are strongly suggested and parameters should minimally include pressure, permeability, and porosity of the injection and confining formations. Monitoring wells are required to check the model data predictions and then necessary updates for corrections should be made to the model
Is fracking behind Oklahoma’s earthquakes?
After the main shock, there were 12 temblors registering at magnitudes of 3.0 or higher and more than 70 quakes with magnitudes of 1.0 to 2.5, Oklahoma Geological Survey research scientist Amie Gibson said Sunday.When the New York Times covered the story they got a quote on the increasing frequency of earthquakes in the state from Austin Holland, a research seismologist with the Oklahoma Geological Survey, a state agency:
“We really hope that the 5.6 was the main shock because I don’t want to see anything like that again, personally. It would be ignorant to assume anything right now, because who would assume that we’d have the two biggest ones in one day?” Gibson said.
Before Saturday night, the strongest earthquake recorded was April 9, 1952, in El Reno, according to the geological survey. Its magnitude was 5.5.
U.S. Geological Survey geophysicist Don Blakeman said the agency doesn’t know why Saturday’s quakes struck so close together.
“We have not a clue,” Mr. Holland said of the increase. “It could be a natural cycle; we just don’t know.”Unfortunately the New York Times reporter either didn’t ask or didn’t know about a study that Mr. Holland published in August 2011 that explored the possible connection between hydraulic fracturing and increased seismic activity in a similar series of quakes that occurred south of Sparks. The report — “Examination of Possibly Induced Seismicity from Hydraulic Fracturing in the Eola Field, Garvin County, Oklahoma” — goes through the existing evidence linking fracking and earthquakes step-by-step. Holland says there is a possibility that the two are linked but that data uncertainties keep him from saying so with absolute conviction. From the summary of the report (emphasis mine):
On January 18, 2011, The Oklahoma Geological Survey (OGS) received a phone call from a resident living south of Elmore City, in Garvin County, Oklahoma, that reported feeling several earthquakes throughout the night. The reporting local resident had also offered that there was an active hydraulic fracturing project occurring nearby.Mr. Holland is skating into dangerous territory with this research. Oklahoma is a national leader in natural gas production, and taxes on it are a big source of revenue. From OK Policy Institute:
Upon examination there were nearly 50 earthquakes, which occurred during that time. After analyzing the data there were 43 earthquakes large enough to be located, which from the character of the seismic recordings indicate that they are both shallow and unique.
[..]
The strong correlation in time and space as well as a reasonable fit to a physical model suggest that there is a possibility these earthquakes were induced by hydraulic fracturing. However, the uncertainties in the data make it impossible to say with a high degree of certainty whether or not these earthquakes were triggered by natural means or by the nearby hydraulic fracturing operation.
Oklahoma is among the nation’s largest producers of both natural gas and oil: In 2009, almost 1.9 trillion cubic feet of natural gas were produced in Oklahoma. Oklahoma’s natural gas output represented 8.5 percent of total U.S. production, trailing only Texas (7.7 trillion cubic feet) and Wyoming (2.5 trillion).So it’s all eyes on the Okie shakes. This may be just an odd series of seismic events. Or it maybe the canary in the coal mine for hydraulic fracturing.
BTW: The largest gas producers in Oklahoma are not local boys but some pretty heavy hitters.
Source: Oklahoma Corporation Commission: 2009 Report on Oil and Natural Gas Activity Within the State of Oklahoma (page 124)
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