Fracture Processes Induced by Forced Fluid Percolation

Cornet, F. H.

doi:10.1007/978-3-642-77008-1_26

Cited by 15 publications

(9 citation statements)

References 63 publications

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“…Majer 1989). A whole range of experiments on hydraulic fracturing shows, however, that hydraulic fracture propagation is globally quasi‐static (Cornet 1992). Detailed studies on hydrofrac experiments in salt rock have strengthened the interpretation that local tip instabilities of tensile modes are not measurable and not important for the fracturing process (Dahm et al 1999; Manthei et al 2001).…”

Section: Discussionmentioning

confidence: 99%

Acceleration of buoyancy-driven fractures and magmatic dikes beneath the free surface

Rivalta

Dahm

2006

Geophysical Journal International

112

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S U M M A R YBy performing buoyancy-driven fracture experiments in brittle gelatin we observe that the ascent velocity of a fracture containing a finite volume of fluid increases when approaching the free surface. We theoretically describe this free-surface effect and quantify it by introducing an effective depth-dependent fracture toughness and developing an ascent model on the basis of linear fracture mechanics. We develop a successful inversion approach and resolve the actual and critical fracture length and the ascent velocity far away from the free surface from the observation of the fracture tip migration alone. Other parameters, as the fluid volume included in the fracture and the in situ fracture toughness, can be derived. Applying the model and inversion to the 1998 eruption at Piton de la Fournaise, Reunion Island, reveals estimates of the length and critical length of the feeding magma batch, the magma batch volume and the in situ fracture toughness. It further indicates that the ascent velocity of the magma batch was probably much smaller at greater depths and that the batch might have been initiated several months or years before the eruption.

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Section: Discussionmentioning

confidence: 99%

Acceleration of buoyancy-driven fractures and magmatic dikes beneath the free surface

Rivalta

Dahm

2006

Geophysical Journal International

112

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“…[14] Wall rock failure occurs when magma overpressure exceeds a critical value, which depends both on the mechanism of fracturing and on the system geometry. We assume that fractures are opened in tensile regime, as commonly observed in experiments of forced fluid injections [Cornet, 1992]. In this case, host rock fracturing occurs when magma overpressure is twice the tensile strength of the surrounding rocks, assumed constant with time, because the intrusion is spherical [Tait et al, 1989].…”

Section: Episodic Gas Expulsionmentioning

confidence: 99%

A model for episodic degassing of an andesitic magma intrusion

Boichu¹,

Villemant²,

Boudon³

2008

J. Geophys. Res.

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[1] Episodic magmatic degassing has been observed at numerous volcanoes, especially those of intermediate composition. It can span timescales from years to decades. Here we propose a physical model for the degassing of a shallow magma intrusion to explain this phenomenon. The magma cools by convection, which leads to melt crystallization, volatile exsolution, and magma overpressure. When the pressure reaches a critical value, wall rocks fracture and the exsolved gas escapes. The intrusion then returns to the initial lithostatic pressure and a new cooling-crystallization-degassing cycle occurs. A series of such cycles leads to episodic degassing. The trend and timescale of the degassing process are mainly governed by magma cooling. Two degassing regimes are exhibited: an early phase with a high frequency of gas pulses and a later phase with a lower gas pulse frequency. The transition between these two regimes is caused by the viscosity increase when the magma crystallinity exceeds the crystal percolation threshold. We find that the time to this transition is dependent on magma volume, to a first approximation. Where observations are available from sustained geochemical surveillance, the model provides constraints on key aspects of the subsurface magmatic system, with estimation of the volume of an intrusion and tensile strength of the surrounding rocks. It therefore represents a relevant tool for volcanic surveillance and hazard assessment.

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“…The N340 • distribution of VT seismicity which is parallel to the regional orientation of the major horizontal stress is characteristic of the seismicity induced by forced fluid flow. This pattern is reported for seismicity induced by fluid injection experiments in different settings, including geothermal fields, oil or gas fields, and in-situ stress measurements (Cornet 1992; Baria et al 1999). The injections of fluid in the crust induce earthquakes whose locations extend in the direction parallel to the largest regional horizontal stress with the induced seismicity characterized by large numbers of small earthquakes at relatively shallow depths that persist for as long as elevated pore pressures in the hypocentral region continued to exist (Anderson 1936;Healy et al 1968;Haimson and Fairhurst 1969;Pearson 1981).…”

Section: Hydrofracturing Mapped By Vt Event Location At Karthala Volcanomentioning

confidence: 82%

“…This blade-shaped pattern is common for seismicity induced by forced fluid flow, such as in the case of fluid injection experiments in geothermal areas, in an oil and gas context, and hydraulic fracturing tests for stress measurement (e.g. Cornet 1992), and suggests that the Karthala seismicity is driven by hydraulic fracturing.…”

Section: Resultsmentioning

confidence: 97%

“…The similar patterns during both the 1991 and the 1994-1995 seismicity indicate that this forced fluid flow has induced the long lasting brittle fracturing for more than five years. At a macroscopic scale, the VT locations outline a single crack shape driven by internal pore pressure increase as predicted by linear mechanics (Anderson 1936;Cornet 1992;Rubin 1995). The increase in seismicity rate before the eruption occurred (Fig.…”

Section: Hydrofracturing Mapped By Vt Event Location At Karthala Volcanomentioning

confidence: 95%

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Seismic signature of a phreatic explosion: hydrofracturing damage at Karthala volcano, Grande Comore Island, Indian Ocean

2005

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Karthala volcano is a basaltic shield volcano with an active hydrothermal system that forms the southern two-thirds of the Grande Comore Island, off the east coat of Africa, northwest of Madagascar. Since the start of volcano monitoring by the local volcano observatory in 1988, the July 11th, 1991 phreatic eruption was the first volcanic event seismically recorded on this volcano, and a rare example of a monitored basaltic shield. From 1991 to 1995 the VT locations, 0.5

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Fracture Processes Induced by Forced Fluid Percolation

Cited by 15 publications

References 63 publications

Acceleration of buoyancy-driven fractures and magmatic dikes beneath the free surface

Acceleration of buoyancy-driven fractures and magmatic dikes beneath the free surface

A model for episodic degassing of an andesitic magma intrusion

Seismic signature of a phreatic explosion: hydrofracturing damage at Karthala volcano, Grande Comore Island, Indian Ocean

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