Exploration Technique: Core Holes
|Exploration Technique Information|
|Exploration Group:||Drilling Techniques|
|Exploration Sub Group:||Exploration Drilling|
|Parent Exploration Technique:||Exploration Drilling|
|Information Provided by Technique|
|Lithology:||Core holes are drilled to identify lithology and mineralization|
|Stratigraphic/Structural:||Retrieved samples can be used to identify fracture networks or faults|
|Thermal:||Thermal conductivity measurements can be done on retrieved samples.|
Core holes are often referred to as "slim holes," with the distinction that not all slim holes recover core.
A major advantage of core holes is that drilling is not stopped by lost circulation zones; drilling may continue through LC zones as long as fluids are pumped into the well (with resulting cost of lost fluids). This allows exploration wells to be drilled through complex stratigraphic sequences (e.g., volcanic rocks) without stopping to cure the lost circulation (Delahunty et al 2012).
Costs increase with depth over time, and deeper holes require larger initial core size (e.g., Delahunty et al 2012). Cost is also affected by drilling regulations for geothermal test wells, which may require casing string cemented in to a percentage of total depth; these rules typically require 1" cement annulus, which may require reaming of hole to attain.
Schmitt et al 2012, https://www.geothermal-library.org/index.php?mode=pubs&action=view&record=1030354
- Blue Mountain Geothermal Area
- Fort Bliss Area
- Hot Sulphur Springs Area
- Kilauea East Rift Geothermal Area
- Lake City Hot Springs Area
- Long Valley Caldera Geothermal Area
- Newberry Caldera Area
- Steamboat Springs Area
- Vale Hot Springs Area
- Valles Caldera - Redondo Geothermal Area
- Valles Caldera - Sulphur Springs Geothermal Area