Аннотация:The paper discusses the application of petrophysical parameters - hygroscopic moisture and velocity of longitudinal waves to define the argillization zone in two geothermal fields
in the Kuril-Kamchatka island arc. The argillization zone is formed under the action of relatively low temperature fluids in the upper part of a geothermal field. Argillized rocks typically form the uppermost water confining horizon in a structure of a geothermal field in spite of high porosity. Pores are characterized by ultra-small size leading to porosity that is ineffective for fluids flow. One way to determine argillization zone is through rock hygroscopy. This study shows that hygroscopy higher than 1.5-2 percent could be used as an indicator of argillization zone. The behavior of rock sonic velocity under water saturation is considered as another way to recognize the argillization zone in geothermal system. The decrease in sonic velocity after water saturation correlates with high hygroscopy and coincidence with the argillization zone. This leads to the conclusion that the argillization zone and potentially the uppermost water confining horizon of a geothermal field could be easily predicted through rock petrophysical parameters without
field hydrogeological tests and x-ray mineralogical analysis which are labour-consuming and more expensive.