Downhole electrical detection of hydraulic fractures in GT-2 and EE-1
Electrical geophysical methods including mise a la masse and self-potential (SP) for determination of hydraulic fracture characteristics were used at the hot dry rock geothermal project. Electrical and induction logs indicated that the resistivity contrast between the granite and 200/sup 0/C water at the 2926-m (9600-ft) depth is a factor of 1000 or more. Thus the water in a hydraulic fracture, formed to connect two adjacent deep holes, is a good conductor compared to the confining granite. Mise a la masse-type measurements were made to help determine the characteristics for hydraulic fractures formed in each of the two geothermal holes GT-2 and EE-1. Once a hydraulic fracture has been formed, mise a la masse effects are obtained both with the fracture pressurized above hydrostatic and when depressurized to hydrostatic. This indicates that once the fracture has been created, enough natural propping exists that a conductive zone persists even when the fracture is deflated. A fracture was formed in a 18-m (60-ft) zone immediately below 1957 m (6420 ft) in EE-1. Later a set of SP logs was run in this zone with no pressure, with pressure building, with pressure decreasing, and again with the fracture depressurized. Results show that during times of change of parameters in hydraulically fractured regions in the hole, natural SP logging helps to determine the position of the fracture. However, after a fracture has come to equilibrium with fluid parameters such as temperature, pressure, salinity, and pH, an effect of the fracture may not be evident. Self-potential logs provide an excellent method for locating the bottom of steel casing that has been set in the hole.
- Research Organization:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 5384666
- Report Number(s):
- LA-6890-MS
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
HOT-DRY-ROCK SYSTEMS
FRACTURES
INDUCTION LOGGING
SP LOGGING
BOREHOLES
ELECTRICAL SURVEYS
EQUILIBRIUM
GEOTHERMAL EXPLORATION
GEOTHERMAL FLUIDS
GRANITES
HIGH TEMPERATURE
HYDRAULIC FRACTURING
NEW MEXICO
SELF-POTENTIAL SURVEYS
CAVITIES
ELECTRIC LOGGING
EXPLORATION
FAILURES
FLUIDS
FRACTURING
GEOPHYSICAL SURVEYS
GEOTHERMAL SYSTEMS
IGNEOUS ROCKS
NORTH AMERICA
ROCKS
USA
WELL LOGGING
Geothermal Legacy
150301* - Geothermal Exploration & Exploration Technology- Geophysical Techniques & Surveys
150303 - Geothermal Exploration & Exploration Technology- Exploratory Drilling & Well Logging
150906 - Geothermal Engineering- Reservoir Stimulation & Extraction Technology