Tracer Testing

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Exploration Technique: Tracer Testing

Exploration Technique Information
Exploration Group: Downhole Techniques
Exploration Sub Group: Well Testing Techniques
Parent Exploration Technique: Well Testing Techniques
Information Provided by Technique
Stratigraphic/Structural: Fracture zones and formation permeability
Hydrological: Flow rates, flow direction, hydrologic connections, storativity
Tracer Testing:
A method based on injecting chemical tracers into the reservoir and monitoring how long it takes and where those tracers travel. The purpose is to model subsurface hydrothermal flow characteristics.
Other definitions:Wikipedia Reegle

Tracer testing is perhaps the most definitive method for learning about the hydrothermal properties of a geothermal reservoir. A tracer test involves the use of some chemical tracer that can be detected within the reservoir fluids in very small concentrations. The chemical is released into the environment usually through an injection well, and gets distributed throughout the reservoir by natural flow patterns. In the following days or months, water samples are collected from other wells and/or springs throughout the geothermal area, and tested for presents of the tracer. The tracer’s concentrations and travel through the reservoir throughout time is monitored from various observation points allowing researchers to model the hydrothermal characteristics of the reservoir. A tracer can be any chemical that will remain stable in the geothermal environment and be detectible after mixing with the hydrothermal fluids. There are numerous tracers used for geothermal tracer tests and research is continuously being conducted to find the most ideal tracers for each type of reservoir. Some examples of natural tracers are chloride, ammonia, and various stable isotopes of water.[1] Some examples of artificial tracers that have been used are tritium, carboxylic and benzene sulfonic acids, polyaromatic sulfonates, chlorofluorocarbons, hydrofluorocarbons, 2-naphthalene sulfonate, 2.7-naphthalene disulfonate, iodide-125, iodide-131, bromide, Sodium-fluorescein, and fluorescent dyes such as fluorescein and rhodamin.[1][2][3][4][5] Fluorescein is only useful in low temperature reservoirs because it decays too rapidly to be useful at temperatures greater than 250°C.
Use in Geothermal Exploration
Tracer tasting is used in geothermal reservoir engineering to study the hydrologic characteristics of a reservoir. Most often it is used to find the connectivity between injection and production wells. Tracer testing can give information about fluid pathways, rates of flow, permeability, storativity, and fluid mixing in the subsurface. This information is useful for reservoir engineers to determine where to place new injection wells, how to sustainably manage the geothermal resource, and to predict possible cooling of production wells.[5]

Field Procedures
Most often the chemical tracers are injected into the reservoir through an injection well. After the tracers are in the reservoir one or more observation points are used to collect water samples for monitoring. Samples are usually collected at production wells. The intervals at which samples are collected can vary and monitoring often goes on for several months.

Researchers pouring a fluorescent dye tracer into waters at the Blautopf (Blue Pot) spring, an intricate cave system in Germany. For geothermal tracer test the chemical tracer is normally injected through an injection well.[6]

Environmental Mitigation Measures
When conducting a tracer test it is important choose a tracer that will not cause harm to the environment especially if there is any possibility of the chemicals seeping into nearby fresh water supplies.

Best Practices
When planning a tracer test there are a few important aspects to consider:[5]

• What tracer to select

• The amount of tracer to inject

• Where, when, and how often to collect samples

There are numerous tracers that can be used in geothermal reservoirs. When selecting a tracer to use there are some important criteria to keep in mind:[1][5]

• Thermal stability: geothermal reservoirs are hot; the tracer used should be stable at temperatures greater than the highest temperature in the reservoir.

• Low background concentrations: the tracer used should not occur in high levels naturally in the geothermal environment.

• Remain dissolved in fluid: the tracer should not react with or be absorbed by the rocks within the reservoir.

• Low detectability: the tracer used should be detectible in very low concentrations and testing should be easy, fast, and inexpensive. A lot of mixing and dilution can take place while the tracer is being distributed around the reservoir and tracer testing in geothermal environments can sometimes take several months before the tracer travels through the reservoir, so intensive monitoring and analysis is required.

• Environmentally benign: tracers should never cause negative environmental effects.

Potential Pitfalls
Tracer tests can sometime take several months, and continuous water sampling analysis is required while waiting for the tracer to show up.

  1. 1.0 1.1 1.2 PetroWiki. Tracer testing in geothermal reservoirs [Internet]. 2013. PetroWiki. [cited 2013/10/17]. Available from:
  2. Marshall J. Reed. 2007. An investigation of the Dixie Valley geothermal field, Nevada, using temporal moment analysis of tracer tests. In: Proceedings, 32nd Workshop on Geothermal Reservoir Engineering; 2007; Stanford University. Stanford University: (!) ; p. (!)
  3. Peter E. Rose,Stuart D. Johnson,Phaedra Kilbourn. 2001. Tracer Testing at Dixie Valley, Nevada, Using 2-Naphthalene Sulfonate and 2,7-Naphthalene Disulfonate. In: Twenty-Sixth Workshop on Geothermal Reservoir Engineering Stanford University. Twenty-Sixth Workshop on Geothermal Reservoir Engineering Stanford University; 2001; Stanford University. Stanford University: (!) ; p. (!)
  4. P.E. Rose,W.R. Benoit,M.C. Adams. 1998. Tracer Testing at Dixie Valley, Nevada, Using Pyrene Tetrasulfonate Amino G, and Fluorescein. Geothermal Resources Council Transactions. .
  5. 5.0 5.1 5.2 5.3 Gudni Axelsson,Grímur Björnsson,Francisco Montalvo. 2005. Quantitative interpretation of tracer test data. In: World Geothermal Congress 2005; 2005/04/24; Antalya, Turkey. Antalya, Turkey: World Geothermal Congress 2005; p. 24–29
  6. Andreas Kucha. Hydrogeology of the Blautopf spring – Tracer tests in Blauhohle cave [Internet]. 2012. [cited 2013/10/17]. Available from:

Page Area Activity Start Date Activity End Date Reference Material
Tracer Testing (Klein, 2007) Unspecified

Tracer Testing At Coso Geothermal Area (1993) Coso Geothermal Area 1993 1993

Tracer Testing At Coso Geothermal Area (2004) Coso Geothermal Area 2004 2004

Tracer Testing At Coso Geothermal Area (2006) Coso Geothermal Area 2006 2006

Tracer Testing At Dixie Valley Geothermal Area (Reed, 2007) Dixie Valley Geothermal Area 1998 2004

Tracer Testing At East Mesa Geothermal Area (1983) East Mesa Geothermal Area 1983 1983

Tracer Testing At East Mesa Geothermal Area (1984) East Mesa Geothermal Area 1984 1984

Tracer Testing At Fenton Hill HDR Geothermal Area (Callahan, 1996) Fenton Hill HDR Geothermal Area 1995

Tracer Testing At Fenton Hill HDR Geothermal Area (Tester, Et Al., 1982) Fenton Hill HDR Geothermal Area 1982 1982

Tracer Testing At Jemez Pueblo Area (DOE GTP) Jemez Pueblo Area

Tracer Testing At Neal Hot Springs Geothermal Area (U.S. Geothermal Inc., 2012) Neal Hot Springs Geothermal Area 2013 2013

Tracer Testing At Raft River Geothermal Area (1983) Raft River Geothermal Area 1983 1983

Tracer Testing At Raft River Geothermal Area (1984) Raft River Geothermal Area 1984 1984

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