Acoustic emission analysis of a geothermal reservoir and its application to reservoir control

A detailed analysis has been made of acoustic emissions detected during build-up tests in a geothermal production well in Kakkonda geothermal power plant, Japan, in 1982, 1984 and 1985. The three-dimensional structure of the hydrothermal reservoir in the field and its dynamic behavior have been investigated. The shape and location of the cracked reservoir, the fluid paths and degree of communication between the reservoir and the geothermal wells, have been revealed by this analysis. The dependence of AE (acoustic emission) activity on valve operations has also been studied. The stability of crack-like reservoirs depends on the reduction in flow-rate in the reservoir system, the closing rate of the wellhead valve and on intervals between the tests. Reservoir stability has been successfuly achieved during the 1985 test by valve regulation, according to the results of the AE study.