The effect of fluid compressibility and elastic rock properties on deformation of geothermal reservoirs

Juncu, Daniel; Árnadóttir, Þóra; Geirsson, H.; Gunnarsson, Gunnar

doi:10.1093/gji/ggz011

Cited by 14 publications

(16 citation statements)

References 45 publications

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“…However, the fluid volume in the crack can be larger than VDef because of the compressibility difference between hydrothermal fluid and surrounding rock (e.g., Rivalta and Segall 2008). Poroelasticity of the surrounding rock also affect the estimation of the actual fluid volume (e.g., Juncu et al 2019). Moreover, the fluid can be much denser than assumed above, if the fluid is supercritical or a liquid phase.…”

Section: Deflation During Phasementioning

confidence: 98%

The 2018 phreatic eruption at Mt. Motoshirane of Kusatsu–Shirane volcano, Japan: Eruption and intrusion of hydrothermal fluid observed by a borehole tiltmeter network

Terada

Kanda

Ogawa

et al. 2021

Preprint

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We estimate the mass and energy budgets for the 2018 phreatic eruption of Mt. Motoshirane on Kusatsu–Shirane volcano, Japan, based on data obtained from a network of eight tiltmeters and weather radar echoes. The tilt records can be explained by a subvertical crack model. Small craters that were formed by previous eruptions are aligned WNW–ESE, which is consistent with the crack azimuth modeled in this study. The direction of maximum compressive stress in this region is horizontal and oriented WNW–ESE, allowing fluid to intrude from depth through a crack with this orientation. Based on the crack model, hypocenter distribution, and MT resistivity structure, we infer that fluid from a hydrothermal reservoir at a depth of 2 km below Kusatsu–Shirane volcano has repeatedly ascended through a pre-existing subvertical crack. The inflation and deflation volumes during the 2018 eruption are estimated to have been 5.1 * 10 5 and 3.6 * 10 5 m 3 , respectively, meaning that 1.5 * 10 5 m 3 of expanded volume formed underground. The total heat associated with the expanded volume is estimated to have been ≥10 14 J, similar to or exceeding the annual heat released from Yugama Crater Lake of Mt. Shirane and that from the largest eruption during the past 130 yr. Although the ejecta mass of the 2018 phreatic eruption was small, the 2018 MPCG eruption was not negligible in terms of the energy budget of Kusatsu–Shirane volcano. A water mass of 0.1–2.0 * 10 7 kg was discharged as a volcanic cloud, based on weather radar echoes, which is smaller than the mass associated with the deflation. We suggest that underground water acted as a buffer against the sudden intrusion of hydrothermal fluids, absorbing some of the fluid that ascended through the crack.

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Section: Deflation During Phasementioning

confidence: 98%

The 2018 phreatic eruption at Mt. Motoshirane of Kusatsu–Shirane volcano, Japan: Eruption and intrusion of hydrothermal fluid observed by a borehole tiltmeter network

Terada

Kanda

Ogawa

et al. 2021

Preprint

View full text Add to dashboard Cite

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“…Among them the β f can greatly vary depending on the phase state, that is, a single vapor, single liquid, or two-phase liquid-vapor state (Grant and Sorey 1979). If we can estimate β f , we may be able to obtain some information about the phase state of the reservoir (Mastin et al 2009;Kozono et al 2013;Hreinsdóttir et al 2014;Juncu et al 2017Juncu et al , 2019.…”

Section: Implications For the Thermodynamic State Of The Deflated Resmentioning

confidence: 99%

“…Thus, understanding the reservoir state is crucial to evaluating the risk of such hazards. While the estimation of the reservoir state based on a combination of ground deformation and discharge mass data has been made in several geothermal areas (Hreinsdóttir et al 2014;Juncu et al 2017Juncu et al , 2019, there are few case studies regarding active volcanoes. It is necessary to increase detailed studies for other active volcanoes with high risks of phreatic eruption and landslide.…”

Section: Implications For the Thermodynamic State Of The Deflated Resmentioning

confidence: 99%

Quantitative relationship between plume emission and multiple deflations after the 2014 phreatic eruption at Ontake volcano, Japan

Narita

Murakami

Tanaka

2019

Earth Planets Space

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The phreatic eruption of Mount Ontake in 2014 caused local-scale subsidence and a mass discharge of water-vapor plumes from vents. A previous study of InSAR data analysis modeled the local subsidence as a deflation of a shallow hydrothermal reservoir (~ 500 m beneath the vents), and speculated that it was associated with plume emission continuing just after the eruption. In addition, combination of the InSAR and GNSS data implies that another, deeper deflation source (~ 3-6 km beneath the vents) contributes to the baseline contraction of the GNSS data. In this study, we estimated daily mass flux of the emitting plumes using photographed images, and compared the temporal behavior of the discharged mass with that of deflation of the two sources in order to clarify their association. The temporal profiles of the shallow deflation volume and the discharge mass both show evidence of decay, but with different characteristics; the deflation volume progress was approximated by a single exponential decay with a long relaxation time (379-641 days), whereas the discharge mass displayed a sum of a linear trend and an exponential decay with shorter relaxation time (47 days). This discrepancy, along with GNSS data, suggests the contribution of a deep deflation source with a short relaxation time (20-40 days). Estimation of mass balance between the emitting plume and fluids discharged from both shallow and deep sources revealed that more than 70% of the discharged mass came from the deep source. Based on the estimated mass balance, phase state of the shallow reservoir was estimated as a single-phase, liquid-rich reservoir. The fast decay of the deep deflation may reflect rapid depressurization due to violent fluid discharge at the onset of the eruption. In contrast, the slow decay of the shallow deflation suggests that it had a minor role in the eruption. However, such a wet reservoir has the potential to induce volcanic hazard such as snow-melting lahar for future eruptions, requiring monitoring the volcano, which will probably shift to pre-eruptive re-pressurized phase, until the future eruption.

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“…However, its pressure change ( P ) value is too large to be realistic, as we show below. In the following discussions, we assume that the rigidity ( µ ) of the host rock is as low as 0.1-1.0 GPa, a realistic value for hydrothermally altered volcanoes and geothermal fields at shallow depths (e.g., Lynne et al 2013;Juncu et al 2019). The estimated value of �P/µ (2.23) requires P to be more than 230 MPa, which greatly exceeds the tensile strength of hydrothermally altered rock (1-10 MPa, Kumar et al 2011).…”

Section: Source Modelingmentioning

confidence: 99%

Precursory ground deformation of the 2018 phreatic eruption on Iwo-Yama volcano, revealed by four-dimensional joint analysis of airborne and spaceborne InSAR

Narita

Ozawa

Aoki

et al. 2020

Earth Planets Space

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We present detailed maps of local-scale 3D deformation preceding the 2018 phreatic eruption at Iwo-yama volcano (south of Kyushu Island, Japan), using a combination of airborne and spaceborne Interferometric Synthetic Aperture Radar (InSAR) data. The 3D and 2.5D deformation maps obtained at different periods allow us to successfully track their spatiotemporal evolution and to infer the transition of subsurface conditions responsible for the precursory deformation observed from 2014 to 2018. From 2014 to 2016, ground inflation depicted an axisymmetric pattern with the maximum displacement at the center of the deformed area. However, from 2016 to 2018, an inflation peak moved to the southern edge of the area deformed during 2014–2016 and became more localized, which was close to the newly generated vents in the 2018 eruption. Modeling of the inflations suggests that pressurization within a crack at a depth of 150 m beneath the Iwo-yama geothermal area caused the 2014–2016 deformation and had continued until the 2018 eruption. Modeling results highlight the persistence of the local ground inflation pattern just above the southern edge of the crack, which suggests the presence of a shallower inflation source contributing to the local inflation. Consequently, we interpret the sequence of these deformations as follows: from 2014, deeper-rooted fluid started to inject into a fluid-saturated crack at 150-m depth, which caused the 2014–2016 deformation. Then, after 2016, the crack inflation continued because of the continuous fluid injection and formed another pressurized part directly above the southern tip of the crack. Additionally, the results of the time-series analysis of the satellite InSAR data revealed that the local inflation started around April 2017 for which thermal activity including a mud emission became pronounced around the location of the local inflation. As a result of an episodic increase in supply rate of magmatic fluids from a deep magma reservoir from early 2018, a phreatic eruption finally occurred in the vicinity of the most deformed point, providing a clue for predicting future eruption sites, as was also observed in the Hakone 2015 eruption.

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The effect of fluid compressibility and elastic rock properties on deformation of geothermal reservoirs

Cited by 14 publications

References 45 publications

The 2018 phreatic eruption at Mt. Motoshirane of Kusatsu–Shirane volcano, Japan: Eruption and intrusion of hydrothermal fluid observed by a borehole tiltmeter network

The 2018 phreatic eruption at Mt. Motoshirane of Kusatsu–Shirane volcano, Japan: Eruption and intrusion of hydrothermal fluid observed by a borehole tiltmeter network

Quantitative relationship between plume emission and multiple deflations after the 2014 phreatic eruption at Ontake volcano, Japan

Precursory ground deformation of the 2018 phreatic eruption on Iwo-Yama volcano, revealed by four-dimensional joint analysis of airborne and spaceborne InSAR

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