Gas Flux Sampling
Exploration Technique: Gas Flux Sampling
|Exploration Technique Information|
|Exploration Group:||Field Techniques|
|Exploration Sub Group:||Field Sampling|
|Parent Exploration Technique:||Gas Sampling|
|Information Provided by Technique|
|Stratigraphic/Structural:||High flux can be indicative of conduits for fluid flow.|
|Thermal:||Anomalous flux is associated with active hydrothermal activity.|
Gas flux sampling is an exploration technique that measures volatile gases emanating from a hydrothermal system. Typical geothermal resources expel anomalously high concentrations of volatile gases (CO2, CH4, N2O, He, etc.) indicating the presence of permeable and potentially high temperature resources.
Gas flux sampling is considered to be an effective exploration technique for “hidden” geothermal resources that lack obvious surface manifestations, such as fumaroles, geysers, hot springs, etc. Hydrothermal activity brings volatile gases and liquids into the near-surface environment that have different compositions, both chemically and isotopically, than typical meteoric fluids. This process causes a relatively high flux of certain gases compared to what is typical of average background gas concentrations, which is indicative of hydrothermal activity and permeable conduits for fluid flow at depth.
There are several factors that can help indicate where to conduct gas flux sampling in the field; near a known geothermal resource, in geologically or structurally similar settings as a known geothermal resource, or where there has been vegetation kill associated with high CO2 soil concentrations. Prior to sampling it is necessary to understand what the background emissions are by studying the geology, climate, vegetation, and wildlife of the particular environment. Arnorsson, et al., (2006) briefly discuss methods and techniques of sampling fluids from a geothermal system.
There are many ways to measure gas flux as discussed by Lewicki and Oldenburg (2004), most of which utilize some type of accumulation or flux chamber and a field analyzer to determine the flux of hydrothermal gases at each sample point. For example, Bergfeld, et al., (2001) discuss a case study in which the CO2 flux was measured using an infrared gas analyzer and accumulation chamber.
The limitations of different accumulation chambers for measuring the flux of various types of gases should be considered when selecting equipment for use in the field. The distribution and placement of accumulation chambers across the area under study must also be dense enough to achieve adequate resolution when flux measurements are plotted as gas concentration maps during data visualization.
When interpreting gas flux data, analysts should be aware of the different inputs and processes that can influence the flux of hydrothermal gases in the near-surface environment. For example, data from Roosevelt Hot Springs, UT suggests that interaction with gases from microbiological processes and other sources can complicate the interpretation of gas flux and soil-gas measurements over geothermal systems. It should also be noted that the limitations of different gas accumulation chambers are unique, and may cause varying degrees of interference with the natural gas flux through an area. Interference in measuring the true flux of hydrothermal gases may affect the results of geochemical modeling of gas dispersion in the near-surface environment.
- Measuring Volcanic Gases: Soil Efflux
- Potential for Surface Gas Flux Measurements in Exploration and Surface Evaluation of Geothermal Resources
- Strategies for Detecting Hidden Geothermal Systems by Near-Surface Gas Monitoring
- Hg Anomalies in Soils: A Geochemical Exploration Method for Geothermal Areas
- Soil Gas and Related Methods for Natural Resource Exploration
- Deborah Bergfeld, Fraser Goff, Cathy J. Janik. 2001. Elevated carbon dioxide flux at the Dixie Valley geothermal field, Nevada- relations between surface phenomena and the geothermal reservoir. Chemical Geology. 177(1):43–66.
- Sampling and Analysis of Geothermal Fluids
- Akutan Fumaroles Area
- Black Warrior Area
- Brady Hot Springs Area
- Desert Peak Area
- Dixie Valley Geothermal Area
- Haleakala Volcano Area
- Hualalai Northwest Rift Area
- Kawaihae Area
- Kilauea East Rift Geothermal Area
- Lahaina-Kaanapali Area
- Lightning Dock Area
- Long Valley Caldera Geothermal Area
- Lualualei Valley Area
- Maui Area
- Mauna Loa Northeast Rift Area
- Mccoy Geothermal Area
- Mokapu Penninsula Area
- Olowalu-Ukumehame Canyon Area
- Socorro Mountain Area
- Steamboat Springs Area