Geology topics

Jonathan M. Glen

Publications and source records attributed to Jonathan M. Glen.

3 recordsLinked to original sources

USGS2018

Discovery of a blind geothermal system in Southern Gabbs Valley, western Nevada, through application of the play fairway analysis at multiple scales

The Great Basin region is capable of generating much greater amounts of geothermal energy than currently produced. Most geothermal resources in this region are blind, and thus favorable characteristics for geothermal activity must be synthesized and methodologies developed to discover new commercial-grade systems. The geothermal play fairway concept involves integration of multiple parameters indicative of geothermal activity to identify promising areas for new development. In the Nevada play fairway project, geologic, geochemical, and geophysical parameters were initially synthesized to produce a new geothermal potential map of 96,000 km2. Southern Gabbs Valley in western Nevada is a particularly promising site selected for detailed study. It contains favorable structural settings, including Quaternary fault intersections and a displacement transfer zone. Geologic, geophysical, and geochemical techniques were employed to define the most likely sites for high permeability and select targets for temperature-gradient holes. Permeability models were revised to reflect results of detailed analyses and generate new detailed play fairway maps. The most promising site lies in an area of multiple fault intersections in a broader displacement transfer zone directly north of the Petrified Springs dextral fault, as revealed by gravity, magnetic, and MT data. A 2-m temperature anomaly and warm temperature gradient wells (~120oC at ~150 m depth) confirm the presence of a geothermal system and provide initial validation of the play fairway methodology. The system is blind, with no surface hot springs, fumaroles, or paleo-geothermal deposits. Lessons learned in the detailed studies include: 1) initially identified sites commonly include multiple favorable settings at a finer scale; 2) promising sites in Cenozoic basins cannot be recognized without detailed geophysical surveys; and 3) play fairway analysis is critical at multiple scales.

Geothermal Resources Council Transactions↗

USGS2016

GIS methodology for geothermal play fairway analysis: Example from the Snake River Plain volcanic province

Play fairway analysis in geothermal exploration derives from a systematic methodology originally developed within the petroleum industry and is based on a geologic and hydrologic framework of identified geothermal systems. We are tailoring this methodology to study the geothermal resource potential of the Snake River Plain and surrounding region. This project has contributed to the success of this approach by cataloging the critical elements controlling exploitable hydrothermal systems, establishing risk matrices that evaluate these elements in terms of both probability of success and level of knowledge, and building automated tools to process results. ArcGIS was used to compile a range of different data types, which we refer to as ‘elements’ (e.g., faults, vents, heatflow…), with distinct characteristics and confidence values. Raw data for each element were transformed into data layers with a common format. Because different data types have different uncertainties, each evidence layer had an accompanying confidence layer, which reflects spatial variations in these uncertainties. Risk maps represent the product of evidence and confidence layers, and are the basic building blocks used to construct Common Risk Segment (CRS) maps for heat, permeability, and seal. CRS maps quantify the variable risk associated with each of these critical components. In a final step, the three CRS maps were combined into a Composite Common Risk Segment (CCRS) map for analysis that reveals favorable areas for geothermal exploration. Python scripts were developed to automate data processing and to enhance the flexibility of the data analysis. Python scripting provided the structure that makes a custom workflow possible. Nearly every tool available in the ArcGIS ArcToolbox can be executed using commands in the Python programming language. This enabled the construction of a group of tools that could automate most of the processing for the project. Currently, our tools are repeatable, scalable, modifiable, and transferrable, allowing us to automate the task of data analysis and the production of CRS and CCRS maps. Our ultimate goal is to produce a toolkit that can be imported into ArcGIS and applied to any geothermal play type, with fully tunable parameters that will allow for the production of multiple versions of the CRS and CCRS maps in order to better test for sensitivity and to validate results.

Idaho↗

USGS2011

Hotspot: The Snake River geothermal drilling project - An overview

The Snake River volcanic province (SRP) overlies a thermal anomaly that extends deep into the mantle; it represents one of the highest heat flow provinces in North America, and an area with the highest calculated geothermal gradients. This makes the SRP one of the potentially highest producing geothermal districts in the United States. Elevated heat flow is typically highest along the margins of the topographic Snake River Plain and lowest along the axis of the plain, where thermal gradients are suppressed by the Snake River aquifer. Beneath this aquifer, however, thermal gradients rise again and may tap even higher heat flows associated with the intrusion of mafic magmas into a geophysically-imaged mid-crustal sill complex. The primary goal of this project is to evaluate geothermal potential in three distinct settings: (1) the high sub-aquifer geothermal gradient associated with the intrusion of mafic magmas and the release of crustal fluids from the associated wall rocks, (2) the valley-margin settings where surface heat flow may be driven by the up-flow of hot fluids along buried caldera ring-fault complexes, and (3) a more traditional fault-bounded basin with thick sedimentary cover. All settings are found within the central or western Snake River Plain and represent previously untested targets for geothermal exploration. Our first drill site tests the extent of geothermal resources along the axis of the plain, beneath the Snake River aquifer, in an area where elevated groundwater temperatures imply a significant flux of conductive or advective heat flow from below. Our second drill site assesses the geothermal potential of up-flow zones along a buried caldera margin, in an area of known geothermal potential (Twin Falls geothermal district). Further studies will include seismic reflection-refraction surveys, gravity-magnetic surveys, and downhole geophysical logs.

Idaho↗