General characterization of the mechanical behaviour of different volcanic rocks with respect to alteration

Pola, Antonio; Crosta, Giovanni B.; Fusi, Nicoletta; Castellanza, Riccardo

doi:10.1016/j.enggeo.2013.11.011

Cited by 111 publications

(64 citation statements)

References 49 publications

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“…We conclude therefore that bio-encrustation and manganese coating may have played an important role in weakening lava sample NA039-056. Alteration has been previously shown to weaken volcanic rocks (Pola et al 2014;Wyering et al 2014;Heap et al 2015b). Permeability measurements show that permeability increases as porosity increases, in accordance with other measurements on basaltic andesites and andesites (Farquharson et al 2015;Kushnir et al 2016;Heap and Kennedy 2016).…”

Section: Discussionsupporting

confidence: 89%

Flank instability assessment at Kick-’em-Jenny submarine volcano (Grenada, Lesser Antilles): a multidisciplinary approach using experiments and modeling

et al. 2016

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Kick-'em-Jenny (KeJ)-located ca. 8 km north of the island of Grenada-is the only active submarine volcano of the Lesser Antilles Volcanic Arc. Previous investigations of KeJ revealed that it lies within a collapse scar inherited from a past flank instability episode. To assess the likelihood of future collapse, we employ here a combined laboratory and modeling approach. Lavas collected using a remotely operated vehicle (ROV) provided samples to perform the first rock physical property measurements for the materials comprising the KeJ edifice. Uniaxial and triaxial deformation experiments showed that the dominant failure mode within the edifice host rock is brittle. Edifice fractures (such as those at Champagne Vent) will therefore assist the outgassing of the nearby magma-filled conduit, favoring effusive behavior. These laboratory data were then used as input parameters in models of slope stability. First, relative slope stability analysis revealed that the SW to N sector of the volcano displays a deficit of mass/volume with respect to a volcanoid (ideal 3D surface). Slope stability analysis using a limit equilibrium method (LEM) showed that KeJ is currently stable, since all values of stability factor or factor of safety (Fs) are greater than unity.The lowest values of Fs were found for the SW-NW sector of the volcano (the sector displaying a mass/volume deficit). Although currently stable, KeJ may become unstable in the future. Instability (severe reductions in Fs) could result, for example, from overpressurization due to the growth of a cryptodome. Our modeling has shown that instabilityinduced flank collapse will most likely initiate from the SW-NW sector of KeJ, therefore mobilizing a volume of at least ca. 0.7 km 3 . The mobilization of ca. 0.7 km 3 of material is certainly capable of generating a tsunami that poses a significant hazard to the southern islands of the West Indies.

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Section: Discussionsupporting

confidence: 89%

Flank instability assessment at Kick-’em-Jenny submarine volcano (Grenada, Lesser Antilles): a multidisciplinary approach using experiments and modeling

et al. 2016

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“…Due to limited data and complex interactions between rock properties and postdeposition alteration and mineralization (e.g., Pola et al 2014;Kanakiya et al 2017), it is difficult to isolate the effects burial diagenesis (e.g., Wadsworth et al 2016). In our study, these fluctuations have been attributed to the variations in primary lithological textures and microstructure as well as secondary alteration, dissolution, and re-precipitation.…”

Section: Effect Of Increased Depth On Physical Propertiesmentioning

confidence: 99%

Matrix permeability of reservoir rocks, Ngatamariki geothermal field, Taupo Volcanic Zone, New Zealand

et al. 2018

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The Taupo Volcanic Zone (TVZ) hosts 23 geothermal fields, seven of which are currently utilised for power generation. Ngatamariki geothermal field (NGF) is one of the latest geothermal power generation developments in New Zealand (commissioned in 2013), located approximately 15 km north of Taupo. Samples of reservoir rocks were taken from the Tahorakuri Formation and Ngatamariki Intrusive Complex, from five wells at the NGF at depths ranging from 1354 to 3284 m. The samples were categorised according to whether their microstructure was pore or microfracture dominated. Image analysis of thin sections impregnated with an epoxy fluorescent dye was used to characterise and quantify the porosity structures and their physical properties were measured in the laboratory. Our results show that the physical properties of the samples correspond to the relative dominance of microfractures compared to pores. Microfracture-dominated samples have low connected porosity and permeability, and the permeability decreases sharply in response to increasing confining pressure. The pore-dominated samples have high connected porosity and permeability, and lower permeability decrease in response to increasing confining pressure. Samples with both microfractures and pores have a wide range of porosity and relatively high permeability that is moderately sensitive to confining pressure. A general trend of decreasing connected porosity and permeability associated with increasing dry bulk density and sonic velocity occurs with depth; however, variations in these parameters are more closely related to changes in lithology and processes such as dissolution and secondary veining and re-crystallisation. This study provides the first broad matrix permeability characterisation of rocks from depth at Ngatamariki, providing inputs for modelling of the geothermal system. We conclude that the complex response of permeability to confining pressure is in part due to the intricate dissolution, veining, and recrystallization textures of many of these rocks that lead to a wide variety of pore shapes and sizes. While the laboratory results are relevant only to similar rocks in the Taupo Volcanic Zone, the relationships they highlight are applicable to other geothermal fields, as well as rock mechanic applications to, for example, aspects of volcanology, landslide stabilisation, mining, and tunnelling at depth.

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“…Hydrothermal alteration can drastically change the elastic wave velocities and permeabilities of rock in both the natural and laboratory environment (Jaya et al 2010;Kristinsdóttir et al 2010;Pola et al 2014). However, coupled studies of physical properties such as porosity, permeability, and strength on geothermal reservoir rocks have not been extensively presented.…”

Section: Previous Studies Of Relevancementioning

confidence: 99%

“…By proxy, the study of rocks from volcanic edifices can help to boost the understanding of processes within geothermal reservoirs especially with regard to microfractures, which play an essential role in controlling strength, porosity, permeability, elastic wave velocities, and elastic moduli of rocks (Wu et al 2000;Guéguen and Schubnel 2003;Pereira and Arson 2013;Faoro et al 2013;Pola et al 2014;Heap et al 2014). For example, Vinciguerra et al (2005) studied the influence of thermal stressing on basaltic samples.…”

Section: Previous Studies Of Relevancementioning

confidence: 99%

“…The geometry of the pores also has a significant role in the strength of the materials both intrinsically and with respect to the direction of stress (Luping 1986). The microstructure of rocks can be changed by increasing the crack damage (by mechanical and/or thermal stresses) as well as hydrothermal alteration (Heap et al 2009;Nara et al 2011;Pola et al 2014); these changes can be observed through the evaluation of destructive and nondestructive physical property measurements (Pola et al 2012 and references therein;Sousa et al 2005). Further, Pola et al (2014) also show that hydrothermal alteration of volcanic rocks can either strengthen or weaken rocks by decreasing or increasing their porosity, respectively.…”

Section: Previous Studies Of Relevancementioning

confidence: 99%

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Physical property relationships of the Rotokawa Andesite, a significant geothermal reservoir rock in the Taupo Volcanic Zone, New Zealand

et al. 2014

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Background: Geothermal systems are commonly hosted in highly altered and fractured rock. As a result, the relationships between physical properties such as strength and permeability can be complex. Understanding such properties can assist in the optimal utilization of geothermal reservoirs. To resolve this issue, detailed laboratory studies on core samples from active geothermal reservoirs are required. This study details the results of the physical property investigations on Rotokawa Andesite which hosts a significant geothermal reservoir. Methods:We have characterized the microstructure (microfracture density), porosity, density, permeability, elastic wave velocities, and strength of core from the high-enthalpy Rotokawa Andesite geothermal reservoir under controlled laboratory conditions. We have built empirical relationships from our observations and also used a classical micromechanical model for brittle failure. Further, we compare our results to a Kozeny-Carman permeability model to better constrain the fluid flow behavior of the rocks. Results: We show that the strength, porosity, elastic moduli, and permeability are greatly influenced by pre-existing fracture occurrence within the andesite. Increasing porosity (or microfracture density) correlates well to a decreasing uniaxial compressive strength, increasing permeability, and a decreasing compressional wave velocity. Conclusions:Our results indicate that properties readily measurable by borehole geophysical logging (such as porosity and acoustic velocities) can be used to constrain more complex and pertinent properties such as strength and permeability. The relationships that we have provided can then be applied to further understand processes in the Rotokawa reservoir and other reservoirs worldwide.Keywords: Geothermal; Uniaxial compressive strength; Permeability; Physical properties; Elastic modulus; Microstructure BackgroundFractures on multiple scales are the dominant control on fluid flow in most geothermal systems worldwide. Geothermal environments are prone to variable heat fluxes, dynamic fluid flow regimes, and active tectonics which impact the physical and mechanical properties of the reservoir rocks in which they are hosted. The influence of such a dynamic environment can render the host rocks highly altered, fractured, and microstructurally complex. As a result, the empirical correlation of physical properties to

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General characterization of the mechanical behaviour of different volcanic rocks with respect to alteration

Cited by 111 publications

References 49 publications

Flank instability assessment at Kick-’em-Jenny submarine volcano (Grenada, Lesser Antilles): a multidisciplinary approach using experiments and modeling

Flank instability assessment at Kick-’em-Jenny submarine volcano (Grenada, Lesser Antilles): a multidisciplinary approach using experiments and modeling

Matrix permeability of reservoir rocks, Ngatamariki geothermal field, Taupo Volcanic Zone, New Zealand

Physical property relationships of the Rotokawa Andesite, a significant geothermal reservoir rock in the Taupo Volcanic Zone, New Zealand

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