Exploratory Boreholes

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Exploration Technique: Exploratory Boreholes

Exploration Technique Information
Exploration Group: Drilling Techniques
Exploration Sub Group: Exploration Drilling
Parent Exploration Technique: Exploration Drilling
Information Provided by Technique
Lithology: Can provide core or cuttings
Stratigraphic/Structural: Identify stratigraphy and structural features within a borehole
Hydrological: -Water samples can be used for geochemical analysis
-Fluid pressures can be used to estimate flow rates
Thermal: -Temperatures can be measured within the hole
-Information about the heat source
Exploratory Boreholes:
An exploratory borehole is drilled for the purpose of identifying the lithological, structural, hydrological, or thermal characteristics of a geothermal resource. Exploratory boreholes are used to locate and roughly define the potential power output of a resource.
Other definitions:Wikipedia Reegle

Exploratory boreholes are drilled to further define or constrain a particular hydrothermal resource. This could be done before any other drilling or to expand and learn more about the dimensions of an existing geothermal power facility.

Note: the terms exploratory wells and exploratory boreholes have been used interchangeably in the geothermal and oil and gas industries. Technically the difference is that a borehole does not produce fluid and a well does.

Use in Geothermal Exploration
Exploration boreholes can be used for many purposes in the geothermal industry. They can provide critical information about the resource at depth allowing developers to better understand the potential power output from a particular area. Exploratory boreholes are also useful for existing geothermal power facilities interested in expanding their resource. Drilling tends to be the most expensive phase of developing a geothermal resource; so many other exploration techniques are done prior to exploratory drilling (Jennejohn, 2009; FIGA, 2011). However, drilling is the only way to verify that the resource is capable of producing sufficient hydrothermal fluids for power generation.
Related Techniques
Thermal gradient holes (TGH) may be drilled prior to any other drilling techniques. TGH are typically narrow and shallow, but can still locate anomalous geothermal gradients, and depending on the drilling conditions, they are often cost effective (Jennejohn, 2009).

A pressure temperature log is generated from a tool sent down a hole, similar to TGH, but accounts for other properties. A pressure temperature log can be done in an exploratory borehole. See Pressure Temperature Log to learn more about this technique.


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