Assessing Structural Controls on Geothermal Fluids from a Three-dimensional Geophysical Model of Warner Valley, Oregon USA (original) (raw)
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3D Geophysical and Hydrologic Characterization of Geothermal Systems in Warner Valley, Oregon USA
2020
Warner Valley in southern Oregon (USA) hosts a geothermal system characterized by several thermal springs and siliceous sinter mounds. Crump geyser, that issued from a well soon after being drilled in 1959 on the west side of the valley, underwent frequent eruptions of boiling water. These manifestations prompted several geological, geochemical, and geophysical investigations of the valley’s geothermal resources. The present work focuses on 3D potential field modeling, incorporating a diverse range of datasets, aimed at characterizing the structural setting of the natural hydrothermal system around Crump geyser. Warner Valley forms a narrow north-south trending extensional basin that developed as an asymmetric graben in a tectonically complex region situated in the northwest corner of the Basin and Range Province. The regional geology consists predominantly of interbedded Neogene sediments and Neogene to Paleogene volcanics that have been faulted by a series of obliquely oriented NW...
Geothermal Resources …, 2006
Although conventional geothermal systems have been successfully exploited for electrical production and district heating in many parts of the world, exploration and development of new systems is commonly hampered by the risk of unsuccessful drilling. A major problem in selecting drill sites is that existing geothermal systems are generally poorly characterized in terms of favorable settings and structural-stratigraphic controls. In order to characterize the structural controls on geothermal systems in active extensional settings, we have analyzed numerous fields in the western Great Basin (USA) and western Turkey through integrated geologic and geophysical investigations. Methods include detailed geologic mapping, structural analysis of faults, detailed gravity surveys, studies of surficial geothermal features (e.g., travertine, sinter, springs, and fumaroles), shallow temperature surveys, and geochemical analyses. Our findings suggest that many fields occupy a) discrete steps in normal fault zones (e.g.,
Characterization of a geothermal system in the Upper Arkansas Valley, CO
2009
The past four years, geophysics students and faculty from Colorado School of Mines and Boise State University have studied the subsurface in the Upper Arkansas Valley, Colorado, using a combination of geological and geophysical methods. Here, we present and integrate their results from seismic, self-potential and gravity data, as well as water temperature measurements in local wells to ascertain the overall basin structure and investigate a geothermal system in the Mt. Princeton area. We conclude that a shallow orthogonal fault system in this area appears to be responsible for the local geothermal signature at and near the surface. The extent to which high temperatures exist throughout the deeper basin is still under investigation.
Geothermics, 2014
In this study, integrated coupled process modeling and field observations are used to build a threedimensional hydrogeological and geomechanical model of an Enhanced Geothermal System (EGS) in the northwestern part of The Geysers geothermal field, California. We constructed a model and characterized hydraulic and mechanical properties of relevant geological layers and a system of multiple intersecting shear zones. This characterization was conducted through detailed coupled process modeling of a oneyear injection stimulation with simultaneous field monitoring of reservoir pressure, microseismicity, and surface deformations. The analysis of surface deformations was found to be particularly challenging as the subtle surface deformations caused by the injection taking place below 3 km depth are intermingled with deformations caused by both tectonic effects and seasonal surface effects associated with rainfall. However, through a detailed analysis of the field data we identified deformations associated with injection. Hydraulic and mechanical properties of relevant rock layers and shear zones were determined using a 3D hydrogeological and geomechanical model. Hydraulic properties were determined using inverse analysis by fitting the pressure evolution in monitoring wells surrounding the injection well. Mechanical properties were estimated by comparison of the predicted microseismicity potential with the observed microseismicity and by fitting the predicted vertical displacement with the surface deformations measured by satellite. The results show the critical importance of considering the regional fault system, especially reservoir-level faults and shear zones that modify injection water flow and steam pressure diffusion. In the vicinity of the EGS Demonstration Project, fluid flow pathways and pressure diffusion fronts appears to be at a maximum along N130 oriented shear zones and at a minimum along N50 oriented shear zones. Evidence for this comes from microseismic event hypocenters which extend several kilometers horizontally from the injection well and deep into a recent granitic intrusion that underlies the high temperature reservoir.
2010
Although conventional geothermal systems have been successfully exploited for electrical production and district heating in many parts of the world, exploration and development of new systems is commonly hampered by the risk of unsuccessful drilling. A major problem in selecting drill sites is that existing geothermal systems are generally poorly characterized in terms of favorable settings and structural-stratigraphic controls. In order to characterize the structural controls on geothermal systems in active extensional settings, we have analyzed numerous fields in the western Great Basin (USA) and western Turkey through integrated geologic and geophysical investigations. Methods include detailed geologic mapping, structural analysis of faults, detailed gravity surveys, studies of surficial geothermal features (e.g., travertine, sinter, springs, and fumaroles), shallow temperature surveys, and geochemical analyses. Our findings suggest that many fields occupy a) discrete steps in normal fault zones (e.g., Desert Peak, Brady's, Nevada, USA; and Simav, Turkey); b) intersections between normal faults and transversely oriented oblique-slip faults (Astor Pass, Nevada, and Salihli, Turkey); c) overlapping oppositely dipping normal fault zones (e.g., Salt Wells, Nevada, USA), d) terminations of major normal faults (e.g.,
2003
We apply a new method to target potential geothermal resources on the regional scale in the Great Basin by seeking relationships between geologic structures and GPS-geodetic observations of regional tectonic strain. First, we establish a theoretical basis for understanding how the rate of fracture opening can be related to the directional trend of faults within the regional-scale strain field. Second, we develop a strain-structure methodology that uses a digitized database of Quaternary fault strikes and velocities of GPS stations. Results of our strain-structure analysis on the regional scale show a spatial relationship between known geothermal activity and (1) change in the direction of fault orientations, (2) change in the direction of extensional strain, and (3) the magnitude of extensional strain, especially fault-normal extension associated with shear strain. In contrast, the dilitation component of strain is not a significant indicator of geothermal activity in the Great Basin. Using the observed relationships between strain and structure, the NE-SW trending Humboldt structural zone (HSZ) in northeastern Nevada is clearly identifiable as a regional geothermal target. Based on our detection of an anomalous high in fault-normal extensional strain, we identify Buffalo Valley toward the NE extent of the HSZ as a potential geothermal target to be further explored using GPS. We therefore recommend investigating Buffalo Valley with fine spatial resolution (~10 km rather than the current ~100 km) using a dense GPS network to assess its geothermal potential, by comparison of strain-structure relationships with current powerproducing areas within the HSZ.
…, 2007
The White River altered area, Washington, and the Goldfi eld mining district, Nevada, are nearly contemporaneous Tertiary (ca. 20 Ma) calc-alkaline igneous centers with large exposures of shallow (<1 km depth) magmatic-hydrothermal, acid-sulfate alteration. Goldfi eld is the largest known high-sulfi dation gold deposit in North America. At White River, silica is the only commodity exploited to date, but, based on its similarities with Goldfi eld, White River may have potential for concealed precious and/or base metal deposits at shallow depth. Both areas are products of the ancestral Cascade arc. Goldfi eld lies within the Great Basin physiographic province in an area of middle Miocene and younger Basin and Range and Walker Lane faulting, whereas White River is largely unaffected by young faults. However, west-northwest-striking magnetic anomalies at White River do correspond with mapped faults synchronous with magmatism, and other linear anomalies may refl ect contemporaneous concealed faults. The White River altered area lies immediately south of the west-northwest-striking White River fault zone and north of a postulated fault with similar orientation. Structural data from the White River altered area indicate that alteration developed synchronously with an anomalous stress fi eld conducive to left-lateral, strike-slip displacement on west-northwest-striking faults. Thus, the White River alteration may have developed in a transient transtensional region between the two strikeslip faults, analogous to models proposed for Goldfi eld and other mineral deposits in transverse deformational zones. Gravity and magnetic anomalies provide evidence for a pluton beneath the White River altered area that may have provided heat and fl uids to overlying volcanic rocks. East-to eastnortheast-striking extensional faults and/or fracture zones in the step-over region, also expressed in magnetic anomalies, may have tapped this intrusion and provided vertical and lateral transport of fl uids to now silicifi ed areas. By analogy to Goldfi eld, geophysical anomalies at the White River altered area may serve as proxies for geologic mapping in identifying faults, fractures, and intrusions relevant to hydrothermal alteration and ore formation in areas of poor exposure.
Reactive transport modeling of the Dixie Valley geothermal area: Insights on flow and geothermometry
Geothermics, 2014
A 2D reactive transport model of the Dixie Valley geothermal area in Nevada, USA was developed to assess fluid flow pathways and fluid rock interaction processes. The model includes two major normal faults and the incorporation of a dual continuum domain to simulate the presence of a small-scale thermal spring being fed by a highly permeable but narrow fracture zone. Simulations were performed incorporating fluid flow, heat conduction and advection, and kinetic mineral-water reactions. Various solute geothermometry methods were applied to simulated spring compositions, to compare estimated reservoir temperatures with "true" modeled reservoir temperatures, for a fluid ascending the simulated fracture and cooling on its way to the surface. Under the modeled conditions (cooling but no mixing or boiling), the classical Na-K(-Ca) geothermometers performed best because these are least affected by mineral precipitation upon cooling. Geothermometry based on computed mineral saturation indices and the quartz geothermometer were more sensitive to re-equilibration upon cooling, but showed good results for fluid velocities above ca. 0.1 m/d and a reactive fracture surface area 1-2 orders of magnitude lower than the corresponding geometric surface area. This suggests that such upflow rates and relatively low reactive fracture surface areas are likely present in many geothermal fields. The simulations also suggest that the presence of small-scale fracture systems having an elevated permeability of 10 −12 to 10 −10 m 2 can significantly alter the shallow fluid flow regime of geothermal systems. For the Dixie Valley case, the model implies that such elevated permeabilities lead to a shallow (less than 1 km) convection cell where superficial water infiltrates along the range front normal fault and connects the small-scale geothermal spring through basin filling sediments. Furthermore, we conclude that a fracture permeability on the order of 10 −12 m 2 may lead to near surface temperature >100 • C whereas a permeability of 10 −10 m 2 is not realistic because this permeability led to extreme upflow velocities and to a short-circuit of the regional fault zone.
geo.igemi.troitsk.ru
Dense magnetotelluric transect data now span the actively extensional Great Basin tectonic province of the western United States and lap onto the stable northern Sierra Nevada and Colorado Plateau platforms. Great Basin coverage shows several highly conductive, sub-horizontal zones in the lower crust interpreted to represent magmatic underplating and hydrothermal fluid exsolution, corroborated by seismic surveying where coincident. These zones typically have steep, dike-like conductors extending surfaceward, several of which appear to feed into recognized high-temperature geothermal systems. They imply an increased contribution from deep magmatic sources to high temperature geothermal systems near-surface relative to previous understanding. Preliminary results suggest that uplifted, presumably quiescent eastern Nevada may in fact be experiencing intense magmatic underplating. That Great Basin geothermal resources typically are associated with conductors is in contrast with classical models based on andesitic stratavolcano systems where resistive zones representing thermal destruction of low-grade clay alteration are considered the norm.
Dense magnetotelluric transect data now span the actively extensional Great Basin tectonic province of the western United States and lap onto the stable northern Sierra Nevada and Colorado Plateau platforms. Great Basin coverage shows several highly conductive, sub-horizontal zones in the lower crust interpreted to represent magmatic underplating and hydrothermal fluid exsolution, corroborated by seismic surveying where coincident. These zones typically have steep, dike-like conductors extending surfaceward, several of which appear to feed into recognized high-temperature geothermal systems. They imply an increased contribution from deep magmatic sources to high temperature geothermal systems near-surface relative to previous understanding. Preliminary results suggest that uplifted, presumably quiescent eastern Nevada may in fact be experiencing intense magmatic underplating. That Great Basin geothermal resources typically are associated with conductors is in contrast with classical...