Montney Python’s Frac’ing Circus
Visitor geology by David Middleton
In a latest submit of mine (ExxonMobil & Chevron Eviscerate Democrat Frac’ing Ban Fantasies) I made this passing remark:
There is no such thing as a proof in any way that frac’ing has ever polluted groundwater or triggered palpable earthquakes.
Concerning my earthquake remark, I used to be referring to particular attribution, not generalized correlations. One very well mannered commentator from British Columbia was fairly insistent that the BC authorities had confirmed that frac’ing is inflicting palpable earthquakes in BC… So insistent that he forwarded me a replica of a BC Oil & Fuel Fee report (hat tip to PeterT). The report goes into nice element correlating the timing of frac’ing operations to the timing and epicenters of two.5 to Four.Four ML earthquakes inside as much as 5 km of the frac’ing operations. Even though such tremors have been related to “solely zero.15 per cent of wellbore stage completions throughout the investigation interval”, they nonetheless decided that 193 tremors will need to have been attributable to frac’ing. 99.85% of particular frac’ing operations weren’t even correlated with such tremors.
The Full Montney: Canada’s Marcellus
Montney tight pure gasoline manufacturing has actually exploded from nothing in 2006 to greater than 30% of Canada’s pure gasoline manufacturing as we speak.
Determine 1. Canada’s Vitality Future: Determine three.16: Pure Fuel Manufacturing by Sort, Reference Case
It’s at present projected that the Montney will account for practically half of Canada’s pure gasoline manufacturing by 2040, with many of the development occurring within the British Columbia portion of the play.
Is it bodily potential for frac’ing to trigger palpable earthquakes?
Sure it’s potential.
Massive-volume disposal of produced brine (Keranen et al. 2014; Schultz et al. 2014; Weingarten et al. 2015) or hydraulic fracturing (Schultz et al. 2015a, 2017;Atkinson et al. 2016; Bao&Eaton2016; Lei et al. 2017) can induce earthquakes by rising pore strain or stress on faults (Ellsworth 2013; Segall & Lu 2015). Essential circumstances for the prevalence of injection-induced seismicity embrace a supply of elevated pore strain, a proximal, critically pressured fault and a pathway for fluid strain to propagate from the injection web site to the fault (Ellsworth 2013; Eaton 2018). Extraction of hydrocarbons from unconventional low-permeability reservoirs, corresponding to organic-rich shale, makes intensive use of hydraulic fracturing to extend reservoir permeability. Earthquakes have been noticed in affiliation with a small fraction of properly completions (Atkinson et al. 2016), but pre-development evaluation is hindered by a paucity of validated predictive fashions to forecast site-specific seismic hazard. Of specific significance is the necessity to obtain a greater understanding of particular geological elements that impression the chance of induced seismicity (Schultz et al. 2016; Ghofrani & Atkinson 2016; Pawley et al. 2018).
Eaton & Schultz, 2018
One of many targets in unconventional useful resource improvement is to keep away from “proximal” faults of all varieties. Frac’ing right into a fault is is a quick observe to a junked & deserted (J&A) wellbore. Nevertheless, some faults are successfully not possible to resolve on reflection seismic knowledge. You’ll be able to’t keep away from a fault, should you can’t see it.
That mentioned, loads of different elements can result in induced seismicity.
In previous a long time, reported instances of induced seismicity within the WCSB (Western Canada Sedimentary Basin) have been attributed to emphasize modifications from hydrocarbon manufacturing (Baranova et al., 1999), enhanced oil restoration (Horner et al., 1994), and wastewater disposal (Schultz et al., 2014).
Atkinson et al., 2016
Atkinson et. al., 2016 established a statistical correlation between frac’ing and induced seismicity within the WCSB… And it could be legitimate… Nevertheless…
Nevertheless, validated predictive fashions should not but out there to evaluate the chance, charges, or magnitudes of induced occasions from particular operations (Nationwide Analysis Council, 2013).
[…]
The causative particulars of the correlation between hydraulic fracturing and seismicity, by way of the way it works on the extent of particular wells, formations, and tectonic regimes are past our present scope, however might be explored in future case research.
Atkinson et al., 2016
They’ve a mannequin they usually have a statistical correlation… Sound acquainted?
Has there been a rise in seismic exercise within the neighborhood of the Montney play?
It is determined by location and timeframe
The entire elevated assumed induced seismicity has occurred within the seismically lively over-pressured portion of the play.
Fluid-injection processes corresponding to disposal of saltwater or hydraulic fracturing can induce earthquakes by rising pore strain and/or shear stress on faults. Pure processes, together with transformation of natural materials (kerogen) into hydrocarbon and cracking to provide gasoline, can equally trigger fluid overpressure. Right here we doc two examples from the Western Canada Sedimentary Basin the place earthquakes induced by hydraulic fracturing are strongly clustered inside areas characterised by pore-pressure gradient in extra of 15 kPa/m. Regardless of intensive hydraulic-fracturing exercise related to useful resource improvement, induced earthquakes are just about absent within the Montney and Duvernay Formations elsewhere.
Eaton & Schultz, 2018
Determine 2. Montney strain gradient, areas of frac’ed Montney wells (black) and earthquakes assumed to have been frac-induced (purple). (Eaton & Schultz, 2018)
Pure Sources Canada has a searchable earthquake database (Earthquakes Canada). I downloaded the info for 3 time intervals for the Lat-Lon vary of the map in Determine 2. The database solely contains 80 earthquakes from 1985-2019, far lower than the 200+ induced quakes asserted by the BCOGC. The extra quakes have been of too low magnitude to register within the nationwide database.
Because of suggestions from the investigation (Appendix 2), eight new seismograph stations (funded by the Fee, Geoscience BC, and the Canadian Affiliation of Petroleum Producers) have been added to
the prevailing two Canadian Nationwide
Seismograph Community (CNSN) stations to supply extra correct detection and site capabilities. Six went on-line in August 2013, and two in November 2014. With the brand new stations the CNSN started recording many extra decrease magnitude occasions than beforehand recorded, enhancing the Fee’s capacity to trace seismicity. This report’s main focus is on the investigation into occasions recorded between August 2013 and October 2014 within the Montney.
The investigation discovered that in this era 231 seismic occasions within the Montney have been attributed to grease and gasoline operations – 38 induced by wastewater disposal and 193 by hydraulic fracturing operations. Not one of the recorded occasions resulted in any accidents, property injury or lack of wellbore containment.
BCOGC
There is no such thing as a “earlier than” on this knowledge set from which to attract a baseline. Does this sound acquainted? Straight evaluating a latest high-resolution knowledge set to the pre-existing low decision knowledge and declaring an anthropogenic anomaly… Very Mannian,
The BCOGC “discovered” 231 seismic occasions, attributed to grease & gasoline operations within the Montney between August 2013 and October 2014 . The Earthquakes Canada database solely tabulates 5 (5) seismic occasions, of all causes, throughout the Montney over that point interval. The Earthquakes Canada database seems to have a constant decision over its report size. There is no such thing as a pattern of detecting decrease magnitude quakes over time. It’s a affordable “earlier than and after” instrument.
Previous to 2005, there was little or no Montney manufacturing (“Pre-Montney”). The “Montney” time interval is from January 1, 2005 to as we speak. “Full Montney” is the interval over which Montney manufacturing has boomed. I’m hard-pressed to see a statistically significant improve in seismic exercise from Pre-Montney to Montney.
Numbers of
QuakesMagnitude≤ 2345≥6Pre-MontneyFeb 2, 1990 to Dec 31, 20042720410MontneyJan 1, 2005 to November 25, 2019811500Full MontneyJan 1, 2013 to November 25, 202063500Quakes per YearMagnitude≤ 2345≥6Pre-MontneyFeb 2, 1990 to Dec 31, 20041.811.340.270.070.00MontneyJan 1, 2005 to November 25, 20190.540.740.340.00zero.00Full MontneyJan 1, 2013 to November 25, 20200.870.430.720.00zero.00
Listed here are maps of the three time intervals:
Determine three. Pre-Montney (Earthquakes Canada) .
Determine 5. Montney (Earthquakes Canada) .
Determine 6. Full-Montney (Earthquakes Canada) .
I suppose a case could possibly be made that the geographical distribution of earthquakes has shifted… if you wish to grasp at straws. Nevertheless, there hasn’t even been statistically significant change within the depths of earthquake epicenters. A shift from regional tectonic causes to anthropogenic causes, typically ends in the epicenters changing into extra shallow.
Determine 7. Earthquake epicenter depths (km). The inexperienced and crimson rectangles signify the depth vary of Montney gasoline manufacturing. Information from Earthquakes Canada.
Can pure earthquakes be distinguished from frac-induced quakes?
Eaton et al., 2013 documented the detailed seismic monitoring of two frac’ing operations.
A analysis mission was undertaken in August 2011 for steady passive monitoring of a multistage hydraulic fracture stimulation of a Montney gasoline reservoir close to Dawson Creek, B.C., with the primary goal of investigating low-frequency traits of microseismic occasions. This work was motivated by a just lately found class of long-period long-duration (LPLD) occasions, interpreted to signify sluggish slip alongside pre-existing fractures. The sector deployment included a 6-level downhole toolstring with low-frequency (Four.5 Hz) geophones and a set of 21 moveable broadband seismograph programs. Time-frequency evaluation of extracted high- and low-frequency microseismic occasions made use of the short-time Fourier rework. Noticed low-frequency microseismic indicators included tremor phenomena at numerous time scales, from just a few seconds to the whole length of high-pressure fluid injection, along with inferred regional earthquakes situated ~150 km from the monitoring web site. Relative to beforehand documented LPLD occasions from the Barnett, variations in low-frequency response for this Montney stimulation are interpreted to replicate a decrease diploma of complexity of preexisting and induced fracture networks. Evaluation of low frequency microseismic indicators reveals promise for bettering geomechanical understanding of fracture processes.
Eaton et al., 2013
They discovered that microseismic occasions occurred all through the operations.
Determine eight. Excessive frequency microseismic occasions throughout frac’ing operations. (Eaton et al., 2013)
Sure… The tremors had unfavourable second magnitudes.
How can an earthquake have a unfavourable magnitude?
Magnitude calculations are primarily based on a logarithmic scale, so a ten-fold drop in amplitude decreases the magnitude by 1.
If an amplitude of 20 millimetres as measured on a seismic sign corresponds to a magnitude 2 earthquake, then:
–10 occasions much less (2 millimetres) corresponds to a magnitude of 1;
–100 occasions much less (zero.2 millimetres) corresponds to magnitude zero;
–1000 occasions much less (zero.02 millimetres) corresponds to magnitude -1.
An earthquake of unfavourable magnitude is a really small earthquake that’s not felt by people.
USGS
They did observe one other phenomena which could possibly be associated to palpable earthquakes: “long-period long-duration (LPLD) occasions, interpreted to signify sluggish slip alongside pre-existing fractures. ” Sadly, additionally they recorded two pure earthquakes that had the identical signature.
You will need to distinguish between potential LPLD occasions related to the hydraulic fracturing remedy and native earthquakes. For instance, Fig 12 reveals quite a few recorded indicators which are interpreted right here as regional earthquakes which are unrelated to this hydraulic fracture remedy.
Eaton et al., 2013
Determine 9. (Left) BCOGC map of frac-induced earthquake clusters (inexperienced circles). (Proper) “earthquake occasions within the Canadian nationwide earthquake catalog from 2000/01/01 to 2013/02/04” (blue circles), pure earthquakes with LPLP signatures (brown oval) and BCOGC inexperienced circles super-imposed. The situation of the Rolla Microseismic Experiment (RME) is denoted by the Four-pointed star southeast of Fort St. John.
Conclusions
It’s successfully not possible to particularly attribute earthquakes to particular frac’ing operations. This 2011 Oklahoma Geological Survey report is the closest factor I’ve seen to constituting proof of a particular frac’ing operation triggering a particular earthquake:
Figuring out whether or not or not earthquakes have been induced in most parts of the steady continent is problematic, due to our poor data of historic earthquakes, earthquake processes and the lengthy recurrence intervals for earthquakes within the steady continent. As well as understanding fluid stream and strain diffusion within the distinctive geology and buildings of an space poses actual and important challenges. The sturdy spatial and temporal correlations to the hydraulic-‐fracturing in Picket Unit B Effectively Four-‐18 actually counsel that the earthquakes noticed within the Eola Subject might have probably been triggered by this exercise. Just because the earthquakes match a easy pore strain diffusion mannequin doesn’t point out that that is the bodily course of that induced these earthquakes.
The variety of historic earthquakes within the space and uncertainties in hypocenter areas make it not possible to find out with a excessive diploma of certainty whether or not or not hydraulic-‐fracturing induced these earthquakes.
Whether or not or not the earthquakes within the Eola Subject have been triggered by hydraulic-‐ fracturing these have been small earthquakes with just one native resident having reported feeling them. Whereas the societal impression of understanding whether or not or not small earthquakes might have been attributable to hydraulic-‐fracturing could also be small, it might doubtlessly assist us study extra about subsurface properties corresponding to stresses at depth, energy of faults, fluid stream, strain diffusion, and long run fault and earthquake behaviors of the steady continent. It could even be potential to establish what standards might have an effect on the chance of anthropogenically induced earthquakes and supply oil and gasoline operators the flexibility to attenuate any antagonistic impacts as recommended by Shapiro et al. (2007).
Holland et al., 2011
Wastewater injection wells very possible have triggered induced seismicity, together with some damaging quakes. It’s additionally possible that oil & gasoline formation, extraction and enhanced restoration processes can even induce seismicity. Whereas it’s potential that frac’ing operations might instantly set off very minor earthquakes, there simply isn’t any direct proof for it… simply fashions and statistical correlations.
References
Atkinson, G.M. et al., 2016. “Hydraulic fracturing and seismicity within the
Western Canada Sedimentary Basin”, Seismol. Res. Lett., 87, 631–647.
B.C. Oil and Fuel Fee (2014). “Investigation of Noticed Seismicity
within the Montney Development”, https://www.bcogc.ca/node/12291/obtain
Eaton, David, et al. “Broadband Microseismic Observations from a Montney Hydraulic Fracture Remedy, Northeastern B.C.” CSEG RECORDER Journal, 1 Mar. 2013, csegrecorder.com/articles/view/broadband-microseismic-observations-from-a-montney-hydraulic-fracture.
Eaton, David & Ryan Schultz. (2018). “Elevated chance of induced seismicity in extremely overpressured shale formations”. Geophysical Journal Worldwide. 214. 751-757. 10.1093/gji/ggy167.
Holland, A. “Examination of Probably Induced Seismicity from Hydraulic Fracturing within the Eola Subject, Garvin County, Oklahoma”. Oklahoma Geological Survey Open-File Report OF1-2011. August 2011.
“Montney Formation Play Atlas NEBC.” BC Oil and Fuel Fee, 16 Jan. 2013, www.bcogc.ca/montney-formation-play-atlas-nebc.
Nationwide Vitality Board. “Canada’s Vitality Future 2018: Vitality Provide and Demand Projections to 2040.” NEB, 28 Aug. 2019, www.cer-rec.gc.ca/nrg/ntgrtd/ftr/2018/index-eng.html.
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