User:Clo234/sandbox

First draft of induced seismicity article:

Induced seismicity can also be caused by the injection of carbon dioxide as the storage step of carbon capture and storage, which aims to sequester carbon dioxide captured from fossil fuel production or other sources in earth’s crust as a means of climate change mitigation. This effect has been observed in Oklahoma and Saskatchewan [3]

Though safe practices and existing technologies can be utilized to reduce the risk of induced seismicity due to injection of carbon dioxide, the risk is still significant if the storage is large in scale. The consequences of the induced seismicity could disrupt preexisting faults in the Earth’s crust as well as compromise the seal integrity of the storage locations. [6]

(Parker)

While there is risk of induced seismicity associated with carbon capture and storage underground on a large scale, it is currently a much less serious risk than other injections. Wastewater injection, hydraulic fracturing, and secondary recovery after oil extraction have all contributed significantly more to induced seismic events in the last several years. [1] There have actually not been any major seismic events associated with carbon injection at this point, whereas there have been recorded seismic occurrences caused by the other injection methods. One such example is massively increased induced seismicity in Oklahoma, USA caused by injection of huge volumes of wastewater into the Arbuckle Group sedimentary rock. [2]

Mohr-Coulomb failure criterion (Clo)

To assess induced seismicity risks associated with carbon capture and storage, one must understand the mechanisms behind rock failure. The Mohr-Coulomb failure criteria describe shear failure on a fault plane [4]. Most generally, failure will happen on existing faults due to several mechanisms: an increase in shear stress, a decrease in normal stress or a pore pressure increase [5]. The injection of supercritical CO2 will change the stresses in the reservoir as it expands, causing potential failure on nearby faults. Injection of fluids also increases the pore pressures in the reservoir, triggering slip on existing rock weakness planes. The latter is the most common cause of induced seismicity due to fluid injection. [5]

The Mohr-Coulomb failure criteria state that

$\tau _{c}=\tau _{0}+\mu (\sigma _{n}+P)$

with $\tau _{c}$ the critical shear stress leading to failure on a fault, $\tau _{0}$ the cohesive strength along the fault, $\sigma _{n}$the normal stress, $\mu$ the friction coefficient on the fault plane and P the pore pressure within the fault [5][4]. When $\tau _{c}$ is attained, shear failure occurs and an earthquake can be felt. This process can be represented graphically on a Mohr’s circle [3] (add link to other Wiki page)

Monitoring techniques (Sofia)

Since geological sequestration of carbon dioxide has the potential to induce seismicity, researchers have developed methods to monitor and model the risk of injection-induced seismicity, in order to better manage the risks associated with this phenomenon. Monitoring can be conducted with measurement from instruments like geophones (link to https://en.wiki.x.io/wiki/Geophone) to measure the movement of the ground. Generally a network of instruments around the site of injection is used, though many current carbon dioxide injection sites do not utilize any monitoring devices. Modeling is an important technique for assessing the potential for induced seismicity, and there are two primary types of models used: physical and numerical. Physical models use measurements from the early stages of a project to forecast how the project will behave once more carbon dioxide is injected, and numerical models use numerical methods to simulate the physics of what is occurring inside the reservoir. Both modeling and monitoring are useful tools to quantify, and thus better understand and mitigate the risks associated with injection-induced seismicity. [3]

SEE SOFIA'S SANDBOX FOR FULL DRAFT INCLUDING EVAN'S PART

[1] NRC - National Research Council (2013). Induced Seismicity Potential in Energy

Technologies. Washington, DC: The National Academies Press. doi:10.17226/13355.

[2] "FAQs." Earthquakes in Oklahoma. N.p., n.d. Web. 27 Apr. 2017. <https://earthquakes.ok.gov/faqs/>.

[3] Verdon, J.P. and Stork, A.L. (2016), Carbon capture and storage, geomechanics and induced seismicity activity. Journal of Rock Mechanics and Geotechnical Engineering. Vol. 8, Pages 928-935. http://doi.org/10.1016/j.jrmge.2016.06.004

[4] Davis, S.D. and Frohlich, C. (1993), Did (or will) fluid injection cause earthquakes? - criteria for a rational assessment. Seismological Research Letters, Vol. 64, No.3- 4.,  https://scits.stanford.edu/sites/default/files/207.full_.pdf

[5] Riffault, J., Dempsey, D., Archer, R., Kelkar, S. and Karra, S. (2011), Understanding Poroelastic Stressing and Induced Seismicity with a Stochastic/Deterministic Model: an Application to an EGS Stimulation at Paralana, South Australia, 2011. 41st Workshop on Geothermal Reservoir

[6] Zoback, M. D., and S. M. Gorelick. "Earthquake triggering and large-scale geologic storage of carbon dioxide." Proceedings of the National Academy of Sciences 109.26 (2012): 10164-0168. Web.