Geologic characteristics of a portion of the Salton Sea geothermal field

Technical Report · Mon Apr 25 04:00:00 EDT 1977

DOI:https://doi.org/10.2172/7287370· OSTI ID:7287370

Tewhey, J D

The examination of drill cuttings and core samples from the Magmamax Nos. 2 and 3 and Woolsey No. 1 wells indicate that the sequence of sedimentary rocks in the Salton Sea geothermal field from the surface to below 4000 ft can be divided into three categories: cap rock, unaltered reservoir rocks, and hydrothermally altered reservoir rocks. The cap rock extends from the surface to a depth of approximately 1100 ft in all three wells. There is evidence to suggest that the cap rock has undergone self-sealing through time as a result of the circulation of hot brine through the rocks. Essentially unaltered reservoir rocks extend from a depth of 1100 ft to approximately 3000 ft. The mineralogical and textural changes that occur at depth can be attributed to the process of hydrothermal alteration. Alteration has occurred in a chemically open system and the important variables in the alteration scheme have been temperature, permeability, brine composition, and rock composition. The transition from unaltered to altered reservoir rocks is marked by the replacement of calcite by epidote. The first appearance of epidote correlates reasonably well with the top of the alteration zone as determined in other studies by electric log analysis. Biotite and chlorite, potential indicators of alteration zones, are considered to be of detrital origin rather than hydrothermal origin. The primary effect of hydrothermal alteration on the reservoir rocks in the Salton Sea geothermal field has been the reduction of porosity and permeability with depth. Petrographic analysis indicates that porosity and permeability in the field is enhanced by the presence of fractures in shales. The geologic picture that emerges from spontaneous potential (SP) log correlation is that of a structural basin whose axis lies to the northwest of Magmamax No. 2. The data suggest that unaltered reservoir rocks on the periphery of the field offer good production possibilities.

• Research Organization: California Univ., Livermore (USA). Lawrence Livermore Lab.
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 7287370
• Report Number(s): UCRL-52267
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
150201* -- Geology & Hydrology of Geothermal Systems-- USA-- (-1989)
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
BIOTITE
BRINES
CALCIUM COMPOUNDS
CALCIUM SILICATES
CAP ROCK
CHEMICAL COMPOSITION
CHLORITE MINERALS
DIAGRAMS
DRILL CORES
ELECTRIC LOGGING
EPIDOTES
GEOLOGICAL SURVEYS
GEOLOGY
GEOTHERMAL FIELDS
GEOTHERMAL WELLS
Geothermal Legacy
HYDROTHERMAL ALTERATION
IRON COMPOUNDS
IRON SILICATES
LITHOLOGY
MICA
MINERALS
OXYGEN COMPOUNDS
PERMEABILITY
PETROLOGY
POROSITY
RESERVOIR ROCK
RESISTIVITY LOGGING
ROCKS
SALTON SEA GEOTHERMAL FIELD
SILICATES
SILICON COMPOUNDS
SP LOGGING
TEMPERATURE DEPENDENCE
TEMPERATURE MEASUREMENT
TRANSITION ELEMENT COMPOUNDS
WELL LOGGING
WELLS