Fracture characteristics and their relationships to producing zones in deep wells, Raft River geothermal area

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1988

OSTI ID:7229314

Rashrash, S M

Fracture characteristics in the sedimentary and metamorphic rocks in the Raft River KGRA of Idaho are analyzed using geological, hydrological and borehole geophysical data from five deep geothermal production wells. Particular emphasis is placed on fracture identification using borehole televiewer logs. Seven fracture orientation sets are recognized in the sedimentary and metamorphic rock units. Although the conventional geophysical logs showed good lithological correlations among the five deep geothermal wells, individual fractures observed using the borehole televiewer logs can be not be traced from well to well. Interpretation of temperature logs, drilling rates and fracture intensity and characteristics indicates that most of the geothermal inflow occurs from three producing zones in each deep geothermal production well. The producing zones are associated mainly with steeply dipping fractures. Single-well pumping tests performed in the site indicate that plots of drawdown per log cycle of time versus discharge rate are nonlinear for each well. This suggests that the calculated values of transmissivity using the single-well pump test data may not represent the actual transmissivity of the reservoir. The multiple-well pumping tests indicate that the geothermal reservoir is anisotropic with transmissivity ranging from 11,200 gpd/ft to 23,900 gpd/ft. The major axis of hydraulic conductivity is in the northeast-southwest direction, which coincides with the orientation of two steeply dipping fracture sets.

• Research Organization: Idaho Univ., Moscow, ID (USA)
• OSTI ID: 7229314
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
150200* -- Geology & Hydrology of Geothermal Systems
FEDERAL REGION X
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOPHYSICAL SURVEYS
GEOTHERMAL SYSTEMS
GEOTHERMAL WELLS
HYDROLOGY
IDAHO
METAMORPHIC ROCKS
NORTH AMERICA
RAFT RIVER VALLEY
RESERVOIR ROCK
ROCKS
SEDIMENTARY ROCKS
SURVEYS
USA
WELLS