Fracture systematics in and around well WD-1, kakkonda geothermal field, japan

Abstract

Interpretation of FMI (Schlumbergers Fullbore Formation MicroImager) logs from well WD-1 and observation of spot cores from well WD-1 in the Kakkonda geothermal field have provided important clues about the nature and configuration of the fracture networks controlling circulation of high-temperature hydrothermal fluid. The fractures comprise four groups: (1) fractures striking NW, (2) high-angle fractures striking NE to E, (3) low-angle fractures striking N, and (4) low-angle fractures striking E. Most permeable fractures in the shallow (<1500 m depth) and deep reservoirs are of group 3, and likely reflect reverse faulting in the modern stress field. Low-angle, group 4 fractures are also permeable, and may have formed in the stress field that existed prior to 0.2±0.1 Ma. Distributions and densities of fractures are comparable in the shallow and deep reservoirs; the temperature difference between the reservoirs is independent of these variables.