Natural Fracture Characterization at the Utah FORGE EGS Test Site: Discrete Natural Fracture Network, Stress Field, and Critical Stress Analysis

Forbes, Bryan; Moore, Joseph N.; Finnila, Aleta; Podgorney, Robert; Nadimi, S.; McIennan, John D.

doi:10.34191/mp-169-n

Cited by 3 publications

(2 citation statements)

References 5 publications

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“…They have been documented by Handwerger and McLennan (2019) and Forbes et al. (2019). The low value of shear‐wave splitting seen in Figure 2 suggests that any fractures in the vicinity of the wellbore may have low compliance, however.…”

Section: Introductionmentioning

confidence: 78%

Elastic wave velocities in a granitic geothermal reservoir

Sayers

2022

Geophysical Prospecting

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Geothermal resources have potential for providing cost-effective and sustainable energy. Monitoring of production-induced changes in geothermal reservoirs using seismic waves requires understanding of the elastic properties of the rock and how they change due to injection of fluids and opening and closing of natural and hydraulic fractures. Pand S-wave velocities measured in a granitic geothermal reservoir using sonic logging are systematically lower than those predicted using the composition of the rock. Cracks may occur in granitic rocks from tectonic stresses and from the thermal expansion mismatch between differently oriented anisotropic crystals. An isotropic orientation distribution of microcracks causes a significant reduction in both the P-and S-velocities, consistent with the observed sonic P-and S-velocities. Vertical fractures cause a difference in the velocity of vertically propagating shear waves polarized parallel and perpendicular to the fractures. An assumption that the lower measured velocities are caused by the presence of vertical fractures is inconsistent with the sonic data. This is because vertical fractures cause a decrease in slow S-wave velocity that greatly exceeds the decrease in P-wave velocity, in contrast to the observed data. The growth of vertical fractures in the geothermal reservoir may be monitored using the difference in velocity of the fast and slow shear waves, while the change in P-velocity in a crossplot of measured P-and slow S-velocities is useful for estimating the ratio of the normal-to-shear compliance of the fractures.

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Section: Introductionmentioning

confidence: 78%

Elastic wave velocities in a granitic geothermal reservoir

Sayers

2022

Geophysical Prospecting

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“…Therefore, a significant amount of effort was used to develop this condition. Values for all stress components were estimated using results from stress testing in Well 58-32 from Phase 2B [51], pore-pressure information (from the pressure boundary condition discussed above), density of the sedimentary materials overlying the granite, and the land-surface topography at the site. Note that any mention of stress refers to the total stress.…”

Section: Stressmentioning

confidence: 99%

A Reference Thermal-Hydrologic-Mechanical Native State Model of the Utah FORGE Enhanced Geothermal Site

et al. 2021

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The Frontier Observatory for Research in Geothermal Energy (FORGE) site is a multi-year initiative funded by the U.S. Department of Energy for enhanced geothermal system research and development. The site is located on the margin of the Great Basin near the town of Milford, Utah. Work has so far resulted in the compilation of a large amount of subsurface data which have been used to improve the geologic understanding of the site. Based on the compiled data, a three-dimensional geologic model describing the structure, composition, permeability, and temperature at the Utah FORGE site was developed. A deep exploratory well (Well 58-32) and numerous tests conducted therein provide information on reservoir rock type, temperature, stress, permeability, etc. Modeling and simulation will play a critical role at the site and need to be considered as a general scientific discovery tool to elucidate the behavior of enhanced geothermal systems and as a deterministic (or stochastic) tool to plan and predict specific activities. This paper will present the development of a reference native state model and the calibration of the model to the reservoir pressure, temperature, and stress measured in Well 58-32.

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Formation of a Large Cold Groundwater Mantle Helium Anomaly and High Temperature Geothermal Resources in Response to Bimodal Magmatism Near Roosevelt Hot Springs and Utah FORGE, Milford Valley, Southwest Utah

Simmons,

Kirby

2024

Geochem Geophys Geosyst

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A large mantle helium anomaly and separate domains of high heat flow are the predominant manifestations of bimodal magmatic activity in the Milford valley. The mantle helium anomaly (1.9–2.6 R/Ra) covers 270 km2 and is subdivided into two separated domains: a cold shallow groundwater regime and high temperature hydrothermal activity. The zone of anomalous heat flow covers >100 km2 and is also subdivided into two adjacent domains, comprising hydrothermal activity at Roosevelt Hot Springs (RHS) (3–7 W/m2) and conductive heat flow (100–180 mW/m2). While the transfer of heat and mantle helium at RHS are coupled, heat and helium transfer are decoupled in the adjacent cold groundwater regime to the west. Both the mantle helium and geothermal anomalies are attributed to recent mafic‐felsic magmatic intrusions of >400 km3, however, the absence of volcanic eruptions <500,000 years indicates magmas stall before rising to shallow crustal level <10 km depth. Deep level magmatism produces a felsic composition melt, which is inferred to be responsible for the widespread and near uniform range of diluted mantle helium values. A thick and impermeable mass of crystalline granitic basement rock at the mid‐crustal level divides the ascent of mantle helium into separate flow paths. It may also impede the rise of buoyant magma trapping thermal energy that facilitates partial melting, slow cooling, and development of a thick thermal aureole. Partitioning of convective and conductive thermal regimes and independent flow paths supplying deeply derived helium characterize the development of a large long‐lived magma‐related geothermal system.

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Natural Fracture Characterization at the Utah FORGE EGS Test Site: Discrete Natural Fracture Network, Stress Field, and Critical Stress Analysis

Cited by 3 publications

References 5 publications

Elastic wave velocities in a granitic geothermal reservoir

Elastic wave velocities in a granitic geothermal reservoir

A Reference Thermal-Hydrologic-Mechanical Native State Model of the Utah FORGE Enhanced Geothermal Site

Formation of a Large Cold Groundwater Mantle Helium Anomaly and High Temperature Geothermal Resources in Response to Bimodal Magmatism Near Roosevelt Hot Springs and Utah FORGE, Milford Valley, Southwest Utah

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