Formation of Composition and Petrophysical Properties of Hydrothermally Altered Rocks in Geothermal Reservoir

Abstract

Since the 60-th years there have been prospecting, explorating and exploiting of geothermal resources in Iceland, Italy, New Zealand, the USA, the Philippines, Japan, Russia (Far East). The present-day geothermal systems attract geologistsí professional attention for some reasons: firstly, as an environmentally-friendly, safe and permanently-supplied source of heat and power; secondly, as natural laboratories where various secondary minerals are formed and volcanites are transformed into metasomatic rocks; thirdly, as potential ore and non-metal deposits. Nowadays there have been stored a lot of information about geothermal systems in the field of mineralogy, geochemistry, ore formation, geothermy. But the petrophysical properties of hydrothermally alterated volcanic rocks have been studied incidentally so far, only in connection with treatment of geophysical, enginering-geological and some other problems. At the same time pertophysical analysis allows to obtain some additional information about formation, evolution and structure of geothermal systems. The petrophysical studies we performed on three geothermal systems of Kuril-Kamchatsky region - Pauzhetskaya, Paratunskaya (Southern Kamchatka) and Okeanskaya (Iturup Isl., the Southern Kurils) allowed to elicit some basic laws of formation of rockís composition and properties under hydrothermally-metasomatical processing influence; to determine the zonal character of alteration of rockís properties cross the geothermal reservoirís section. In addition our investigation to show that complex analysis of petrophysical characteristics along with structuralmineralogical peculiarities of rocks allows to make more precise the structure of geothermal system.