Cyclic soft stimulation (CSS): a new fluid injection protocol and traffic light system to mitigate seismic risks of hydraulic stimulation treatments

Hofmann, Hannes; Zimmermann, Günter; Zang, Arno; Min, Ki‐Bok

doi:10.1186/s40517-018-0114-3

Cited by 72 publications

(45 citation statements)

References 86 publications

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“…Recently, Kwiatek et al (2019) reported on a successful attempt controlling the evolution of seismic magnitudes during an EGS operation by adjusting the stimulation protocol. But whether or not maximum magnitudes of injection-induced seismicity can indeed be controlled and if events have the same magnitude limit as tectonic earthquakes is currently still a matter of debate (e.g., Hofmann et al, 2018;van der Elst et al, 2016). It is generally assumed that small perturbations of effective stresses are sufficient to initiate failure to critically stressed faults (Zoback & Townend, 2001).…”

Section: Discussionmentioning

confidence: 99%

Seismic Moment Evolution During Hydraulic Stimulations

Bentz

Kwiatek

Martínez‐Garzón

et al. 2020

Geophysical Research Letters

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Analysis of past and present stimulation projects reveals that the temporal evolution and growth of maximum observed moment magnitudes may be linked directly to the injected fluid volume and hydraulic energy. Overall evolution of seismic moment seems independent of the tectonic stress regime and is most likely governed by reservoir specific parameters, such as the preexisting structural inventory. Data suggest that magnitudes can grow either in a stable way, indicating the constant propagation of self‐arrested ruptures, or unbound, for which the maximum magnitude is only limited by the size of tectonic faults and fault connectivity. Transition between the two states may occur at any time during injection or not at all. Monitoring and traffic light systems used during stimulations need to account for the possibility of unstable rupture propagation from the very beginning of injection by observing the entire seismicity evolution in near‐real time and at high resolution for an immediate reaction in injection strategy.

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Section: Discussionmentioning

confidence: 99%

Seismic Moment Evolution During Hydraulic Stimulations

Bentz

Kwiatek

Martínez‐Garzón

et al. 2020

Geophysical Research Letters

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“…However, if permeability enhancement and seismicity are decoupled, as we have shown for Ngatamariki, it may be possible (perhaps through "soft stimulation" techniques Hofmann et al, 2018;Yoon et al, 2014) to design injection operations in similar settings elsewhere in order to achieve the desired permeability gain while limiting the number and magnitude of induced seismic events. Lower-temperature resources will not exhibit similar degrees of thermal stimulation, and lower-permeability reservoirs are subject to higher pore pressure perturbations, thus increasing the likelihood of inducing seismicity.…”

Section: Discussionmentioning

confidence: 99%

“…Lower-temperature resources will not exhibit similar degrees of thermal stimulation, and lower-permeability reservoirs are subject to higher pore pressure perturbations, thus increasing the likelihood of inducing seismicity. However, if permeability enhancement and seismicity are decoupled, as we have shown for Ngatamariki, it may be possible (perhaps through "soft stimulation" techniques Hofmann et al, 2018;Yoon et al, 2014) to design injection operations in similar settings elsewhere in order to achieve the desired permeability gain while limiting the number and magnitude of induced seismic events.…”

Section: Discussionmentioning

confidence: 99%

Seismic Response to Injection Well Stimulation in a High‐Temperature, High‐Permeability Reservoir

Hopp

Sewell

Mroczek

et al. 2019

Geochem Geophys Geosyst

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Fluid injection into the Earth's crust can induce seismic events that cause damage to local infrastructure but also offer valuable insight into seismogenesis. The factors that influence the magnitude, location, and number of induced events remain poorly understood but include injection flow rate and pressure as well as reservoir temperature and permeability. The relationship between injection parameters and injection‐induced seismicity in high‐temperature, high‐permeability reservoirs has not been extensively studied. Here we focus on the Ngatamariki geothermal field in the central Taupō Volcanic Zone, New Zealand, where three stimulation/injection tests have occurred since 2012. We present a catalog of seismicity from 2012 to 2015 created using a matched‐filter detection technique. We analyze the stress state in the reservoir during the injection tests from first motion‐derived focal mechanisms, yielding an average direction of maximum horizontal compressive stress (SHmax) consistent with the regional NE‐SW trend. However, there is significant variation in the direction of maximum compressive stress (σ1), which may reflect geological differences between wells. We use the ratio of injection flow rate to overpressure, referred to as injectivity index, as a proxy for near‐well permeability and compare changes in injectivity index to spatiotemporal characteristics of seismicity accompanying each test. Observed increases in injectivity index are generally poorly correlated with seismicity, suggesting that the locations of microearthquakes are not coincident with the zone of stimulation (i.e., increased permeability). Our findings augment a growing body of work suggesting that aseismic opening or slip, rather than seismic shear, is the active process driving well stimulation in many environments.

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“…Recently, cyclic injection designs, together with the prominently applied multistage stimulation (Johri & Zoback 2013), have been among the many candidate treatments attempting to minimize the seismicity associated with stimulation treatments. We note that the step-wise pore pressurizationdepressurization scheme applied in this study has similarities with advanced hydraulic stimulation treatments based on cyclic fluid injection schemes, such as fatigue hydraulic fracturing (Zang et al 2013(Zang et al , 2019 and cyclic soft stimulation (Hofmann et al 2018b(Hofmann et al , 2019. Diverse fracture permeability and frictional strength behavior described with these experiments might also be considered an addition to the laboratory scale observations (e.g.…”

Section: Implications For Natural Fault Systems and Reservoir Stimulamentioning

confidence: 68%

The influence of fault reactivation on injection-induced dynamic triggering of permeability evolution

Yildirim

Elsworth

2020

Geophysical Journal International

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Summary Mechanisms controlling fracture permeability enhancement during injection-induced and natural dynamic stressing remain unresolved. We explore pressure-driven permeability (k) evolution by step-increasing fluid pressure (p) on near-critically-stressed laboratory fractures in shale and schist as representative of faults in sedimentary reservoirs/seals and basement rocks. Fluid is pulsed through the fracture with successively incremented pressure to first examine sub-reactivation permeability response that then progresses through fracture reactivation. Transient pore pressure pulses result in a permeability increase that persists even after the return of spiked pore pressure to the null background level. We show that fracture sealing is systematically reversible with the perturbing pressure pulses and pressure-driven permeability enhancement is eminently reproducible even absent shear slip and in the very short term (order of minutes). These characteristics of the observed fracture sealing following a pressure perturbation appear similar to those of the response by rate-and-state frictional healing upon stress/velocity perturbations. Dynamic permeability increase scales with the pore pressure magnitude and fracture sealing controls the following per-pulse permeability increase, both in the absence and presence of reactivation. However, initiation of the injection-induced reactivation results in a significant increase in the rate of permeability enhancement (dk/dp). These results demonstrate the role of frictional healing and sealing of fractures at interplay with other probable processes in pore pressure-driven permeability stimulation, such as particle mobilization.

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Cyclic soft stimulation (CSS): a new fluid injection protocol and traffic light system to mitigate seismic risks of hydraulic stimulation treatments

Cited by 72 publications

References 86 publications

Seismic Moment Evolution During Hydraulic Stimulations

Seismic Moment Evolution During Hydraulic Stimulations

Seismic Response to Injection Well Stimulation in a High‐Temperature, High‐Permeability Reservoir

The influence of fault reactivation on injection-induced dynamic triggering of permeability evolution

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