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Start Over Author "Kneafsey P" Journal geophysical research letters
5 results on '"Kneafsey P"'

1. In Situ Continuous Monitoring of Borehole Displacements Induced by Stimulated Hydrofracture Growth

Author

Guglielmi, Y, Cook, P, Soom, F, Schoenball, M, Dobson, P, and Kneafsey, T

Subjects
borehole displacements, deep stress environment, foliated metamorphic rock, hydrofracture, induced seismicity, monitoring fracture nucleation and growth, Meteorology & Atmospheric Sciences
Abstract

We provide direct observations of the three-dimensional displacements of a fluid-driven fracture during water injections in a borehole at ∼1.5 km depth in the crystalline rock at the Sanford Underground Research Facility (USA). Micro-shearing of the borehole initiates on a foliation plane at 61% of the minimum principal stress σ3. As the fluid pressure increases further up to 112% of σ3, borehole axial and radial displacements increase with injection time highlighting the opening and sliding of a new hydrofracture growing ∼10 m away from the borehole, in accordance with the ambient normal stress regime and in alignment with the microseismicity. Our study reveals how important it is to consider monitoring zonal deformation in conjunction with pressure and flow to better manage the complex hydromechanical evolution of the growing fracture.

Published
2021

2. Fracture Caging to Limit Induced Seismicity

Author

Frash, LP, Fu, P, Morris, J, Gutierrez, M, Neupane, G, Hampton, J, Welch, NJ, Carey, JW, and Kneafsey, T

Subjects
earthquake, energy, geothermal, risk mitigation, traffic light protocol, Meteorology & Atmospheric Sciences
Abstract

Geothermal resources offer a stable low-carbon energy source. However, geothermal sites can collocate with the hypocenters of large-magnitude seismic events. Large seismic events pose a risk to public safety and are therefore a liability for efforts to develop geothermal resources. Here, we propose “fracture caging” to limit induced seismic event magnitudes and present evidence from numerical model predictions, laboratory experiments, and field observations. Fracture caging involves drilling tactical production wells around a geothermal injection zone to contain fluids in fracture-dominated flow systems. Prior to our work, the effect of small wells on the growth of large fractures and on flow through fractures was subject to debate. Our work shows that production wells can impede fracture growth and contain high-pressure fluids in fracture-dominated rocks. This containment offers a mechanism to limit induced seismicity.

Published
2021

3. Large CO2 and CH4 emissions from polygonal tundra during spring thaw in northern Alaska

Author

Raz‐Yaseef, Naama, Torn, Margaret S, Wu, Yuxin, Billesbach, Dave P, Liljedahl, Anna K, Kneafsey, Timothy J, Romanovsky, Vladimir E, Cook, David R, and Wullschleger, Stan D

Subjects
Earth Sciences, Atmospheric Sciences, Arctic, tundra, carbon fluxes, thaw, pulse, eddy covariance, Meteorology & Atmospheric Sciences
Abstract

The few prethaw observations of tundra carbon fluxes suggest that there may be large spring releases, but little is known about the scale and underlying mechanisms of this phenomenon. To address these questions, we combined ecosystem eddy flux measurements from two towers near Barrow, Alaska, with mechanistic soil-core thawing experiment. During a 2 week period prior to snowmelt in 2014, large fluxes were measured, reducing net summer uptake of CO2 by 46% and adding 6% to cumulative CH4 emissions. Emission pulses were linked to unique rain-on-snow events enhancing soil cracking. Controlled laboratory experiment revealed that as surface ice thaws, an immediate, large pulse of trapped gases is emitted. These results suggest that the Arctic CO2 and CH4 spring pulse is a delayed release of biogenic gas production from the previous fall and that the pulse can be large enough to offset a significant fraction of the moderate Arctic tundra carbon sink.

Published
2017

4. 4D Electrical Resistivity Imaging of Stress Perturbations Induced During High‐Pressure Shear Stimulation Tests

Author

Johnson, T. C., Burghardt, J., Strickland, C., Sirota, D., Vermeul, V., Knox, H., Schwering, P., Blankenship, D., and Kneafsey, T.

Abstract

Fluid flow through fractured media is typically governed by the distribution of fracture apertures, which are in turn governed by stress. Consequently, understanding subsurface stress is critical for understanding and predicting subsurface fluid flow. Although laboratory‐scale studies have established a sensitive relationship between effective stress and bulk electrical conductivity in crystalline rock, that relationship has not been extensively leveraged to monitor stress evolution at the field scale using electrical or electromagnetic geophysical monitoring approaches. In this paper we demonstrate the use time‐lapse 3‐dimensional (4D) electrical resistivity tomography to image perturbations in the stress field generated by pressurized borehole packers deployed during shear‐stimulation attempts in a 1.25 km deep metamorphic crystalline rock formation. Time‐lapse electrical geophysical sensing is used to image 3D changes in rock stress generated by an isolated and pressurized interval of a borehole in a deep, dense, fractured rock formation. Remotely monitoring stress is challenging but important for relating geomechanical behavior to flow pathways during energy productionBulk electrical conductivity is sensitive to stress in crystalline rockTime‐lapse electrical resistivity tomography can be used to remotely monitor 3D changes in effective stress Remotely monitoring stress is challenging but important for relating geomechanical behavior to flow pathways during energy production Bulk electrical conductivity is sensitive to stress in crystalline rock Time‐lapse electrical resistivity tomography can be used to remotely monitor 3D changes in effective stress

Published
2024
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5. Large CO2and CH4emissions from polygonal tundra during spring thaw in northern Alaska

Author

Raz‐Yaseef, Naama, Torn, Margaret S., Wu, Yuxin, Billesbach, Dave P., Liljedahl, Anna K., Kneafsey, Timothy J., Romanovsky, Vladimir E., Cook, David R., and Wullschleger, Stan D.

Abstract

The few prethaw observations of tundra carbon fluxes suggest that there may be large spring releases, but little is known about the scale and underlying mechanisms of this phenomenon. To address these questions, we combined ecosystem eddy flux measurements from two towers near Barrow, Alaska, with mechanistic soil‐core thawing experiment. During a 2 week period prior to snowmelt in 2014, large fluxes were measured, reducing net summer uptake of CO2by 46% and adding 6% to cumulative CH4emissions. Emission pulses were linked to unique rain‐on‐snow events enhancing soil cracking. Controlled laboratory experiment revealed that as surface ice thaws, an immediate, large pulse of trapped gases is emitted. These results suggest that the Arctic CO2and CH4spring pulse is a delayed release of biogenic gas production from the previous fall and that the pulse can be large enough to offset a significant fraction of the moderate Arctic tundra carbon sink. Prethaw carbon flux pulses during thaw offset 46% of CO2summer uptake and added 6% to CH4summer fluxesLaboratory experiment linked pulse emissions to a delayed microbial production mechanismThe spring pulse may be a large underrepresented source of carbon in Arctic regions

Published
2017
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