Interpretation of Well Logging Data on Lahendong Geothermal Field, Indonesia

Abstract

A presence of hydrothermal convection systems in the Lahendong geothermal reservoir is examined using the Rayleigh number (Ra). Interpretation of well logging data on Lahendong geothermal field suggested that the Lahendong field consists of two reservoirs; shallow one with average thickness of about 450 m and deep one with 1200 m thickness. The Rayleigh numbers for shallow and deep reservoirs calculated using permeability of cores are in the range from 0.0027 to 0.51 which are lower than the classical critical Rayleigh number ( °÷39.5) and the critical Rayleigh number (Rc) depending on the over-heat ratio (). Thus, permeability values of the cores are too low for an onset of natural convection. The Ra calculated using permeability values from well tests imply that convection process occurs in shallow and deep reservoirs in the central area in Lahendong, while it occurs only in the deep reservoir in the southern area.