Stress Test

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Exploration Technique: Stress Test

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 distribution and ambient tectonic stresses
Hydrological: Fluid flow direction
Stress Test:
A geologic stress analysis based on images of a borehole wall and hydraulic fracturing tests to characterize fracture orientations and stress magnitudes in order to identify stress planes and zones of potential permeability.
Other definitions:Wikipedia Reegle

A stress test begins with collecting downhole images of the borehole walls. The images are analyzed by geologists for rock type, hydraulic characteristics, and fracture location and orientation. Hydraulic fracturing stress tests are sometimes conducted following the analysis and designed to measure and characterize the formation stress fields.[1] The main purpose of conducting stress tests are to locate planes in the borehole of shear and normal stresses to predict how the well will respond to hydraulic fracturing. After hydraulic fracturing has been conducted the stress fields within the well can be more accurately defined and further hydraulic fracturing may take place.
Use in Geothermal Exploration
Stress tests are used mainly during EGS projects. Determining the ambient state of stress in the formation is important for defining fracture patterns and fluid transport direction.[2]

Field Procedures
Stress tests begin with imaging of the borehole walls in areas of interest. The images are analyzed for fracture orientation, distribution, and size. Natural fractures, drilling induced tensile wall fractures, and borehole breakouts are identified. Then a hydraulic fracturing plan can established based on the data. After hydraulic fracturing is conducted borehole images are taken again and analyzed.

An example of images taken from a well at the Coso Geothermal Area for stress tests. (a) natural fractures, (b) A fracture with significant apparent aperture, (c) fractures caused by drilling, (d) borehole breakouts.[1]

Best Practices
Stress tests normally begin with imaging of the borehole walls for analysis of fracture patterns and indications of stress zones. After a visual analysis hydraulic fracturing is conducted and the borehole walls should be imaged again to analyze how the well responded and determine any zones where permanent permeability might be established.
Potential Pitfalls
Stress tests are expensive and in very hot geothermal environments where the rock becomes plastic fractures might close up soon after the hydraulic fracturing.

  1. 1.0 1.1 Judith M. Sheridan,Stephen H. Hickman. 2004. In situ stress, fracture, and fluid flow analysis in Well 38C-9: an enhanced geothermal system in the Coso geothermal field. In: Twenty-Ninth Workshop on Geothermal Reservoir Engineering. Twenty-Ninth Workshop on Geothermal Reservoir Engineering; 2013/01/01; Stanford, California. Stanford, California: US Geological Survey; p. 9
  2. U.S. Geological Survey. Borehole Imaging of In Situ Stress Tests at Mirror Lake Research Site [Internet]. 2013. U.S. Geological Survey. [cited 2013/10/16]. Available from:

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