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Rychagov S.N., Belousov V.I., Sugrobov V.M., Postnikov A.I. and Alekseev Yu.P.

PROSPECTS OF GEOTHERMAL ENERGY USE IN THE KURIL ISLANDS Rychagov S.N.1, Belousov V.I.1, Sugrobov V.M.1, Postnikov A.I.2 and Alekseev Yu.P.2 1 Institute of Volcanology, FED RAS, Petropavlovsk-Kamchatsky, Russia, E-mail:

rychsn@kcs.iks.ru 2 Science joint-stock company, scow, Russia, E-mail: postnikov@geotherm.ru The Kuril Islands with their unique natural complex are of the greatest importance for geopolitics and social economics of Russia (Fig. 1). Hitherto in the Kuril Islands power engineering operates owing to fuel deliveries and it suffers great difficulties in this connection. At the same time well-known geothermal manifestations and deposits the summary potential electric capacity of which is estimated to be 295 MW per 100 years of exploitation are located in all large islands of the Kuril ridge near the main built-up areas (Strategy, 2001). The Northern Kuril deposit in Paramushir island (as per different data estimated to be from 40 up to 100 MW), Oceanic deposit in Iturup (60 MW) and Mendeleeva-Goryachiy Plyazh in Kunashir (60 MW) are first and foremost among them (Strategy, 2001; Belousov et al., 2002; Rychagov et al., 2004).

Working models of some geothermal manifestations and deposits in the Kuril Islands are represented, their electric and thermal capacity potential is evaluated and prospects of geothermal energy use in the regional economy are shown on the basis of generalisation of results of geological-geophysical studies and prospecting-exploring activity.

This work is performed with financial support of the Federal purpose-oriented programme Social and Economic Development of the Kuril Islands of Sakhalin Region up to 2005 Year, RF Ministry of Economic Development and Trade and Russian Fund of Basic Research (projects 03-05-64044, 05-0579101 and 05-05-74029g).

Figure 1: The physiographic map of Kuril insular arch and main geothermal deposits.

1. , 1. Introduction On the basis of practical studies the new geological objects have been found in volcanoes and hydrothermal systems of recent and ancient insular arches within the last years. These ones are long-living ore-forming hydrothermal-magmatic convective systems in the area of transition from the oceanic crust to the continental earths crust (Rychagov et al., 1999). Under insular arch conditions characterised as subareal ones the upper parts of hydrothermal-magmatic systems are located at the boundary of interaction of three geospheres: atmosphere, hydrosphere and lithosphere. This fact conditions such processes as interaction of hydrothermae with cold meteoric waters, subterranean boiling and steam and gas separation. During volcanic eruptions the great amount of atmospheric gases gets into the depth of several kilometres preconditioning the beginning of phreatic-magmatic and phreatic explosions (Oshawa et al., 2000) as well as activation of hydrothermal processes. Environments where dynamic alteration of thermodynamic parameters causing formation of mixed hydrothermae with different pH and Eh are formed in hydrothermal systems. Increased carbonic acid concentrations in the upper part of hydrothermalmagmatic systems of insular arch volcanism stage are conditioned by specific structuralgeological processes. Since this part of systems is composed mainly by loose rocks preconditions for formation of voluminous magmatic rock bodies are created there. At the stage of insular arch volcanism the greater part of the abyssal high-temperature magmatic melt is localised in the long-living volcanic centre structure itself. Such hold-up of magmatic melts in the upper horizons of the earths crust causes relatively proportional and gradual heat dispersion and continuos degasation of melts and, consequently, stable recharge of the system. Presence of sub-surface horizon of bicarbonaceous carbonated hydrothermae are typical for the hydrochemical structure of this type hydrothermalmagmatic systems. Intensive 2 release and extensive vaporisation cause formation of thick areas with sulphate-acid alterations as well as silicified rocks and deposition of great quantity of metals. These structure roots submerge into the depth of many kilometres and dozens of them down to the primitive basaltic magma generation levels in the upper mantle. The hydrothermal cell overbuilds the magmatic convective one and therefore controls distribution of chemical elements including ore, alkaline and rare ones in the earths crust upper horizons. Thus it is a self-isolating geological system. Just this property of systems predetermines large geothermal, epithermal ore, copper-porphyritic and other deposit formation in their bowels (Rychagov, 2003). The complex study of volcanoes and hydrothermal systems of the Kuril insular arch allowed to find the series of such Rychagov S.N., Belousov V.I., Sugrobov V.M., Postnikov A.I. and Alekseev Yu.P.

hydrothermal-magmatic systems which are promising for the regional economy use.

2. The Nothern Paramushir Hydrothermal-Magmatic system and Northern Kuril geothermal deposit The interest in study of the Northern Paramushir hydrothermal-magmatic system is determined by the specific conditions of distribution, accumulation and dynamics of the regional surface and subsurface waters as well as by particular features of the system itself structure. These are insular location of the object under study (Paramushir island and the Great Kuril range) at the joint of the oceanic earths crust with that of continental type, location in the large, complex and long-developing tectonic-magmatic structure of the Vernadskogo volcanic range, wide development of volcanogenic formations of rocks with well-collecting properties, presence of the heating source of the unknown nature and parameters in the system bowels at more than 2-3 km depth and the fact that recent volcanism manifestations are represented by the active volcano Ebeko and Holocenic volcano Neozhydanny considered to be extinct.

Paramushir and Shumshu islands are the relatively upstanding blocks of the earths crust and they are considered as the southern extension of the Pribrezhny horst in South Kamchatka (Aprelkov, 1971). Paramushir island northern part is composed by rocks of the age beginning from Upper Miocene-Pliocene and up to Recent one. The foundation consists of sedimentary rocks of the Paramushir complex of suits. The most ancient rocks among those laid bare are represented by layered volcanomict sandstones, tuffs, tuffgritstones and tuff-aleurolites (the Okhotsk suite, N13 N21) with total thickens from up to 3000 m. Deposits in the Okhotsk suite section upper part are represented by conglomerates, brecciae et al. lying eastward almost aflat or at the angle 5-100. Their visible thickness is up to 500 m. The Neogene deposition section is crowned with the oceanic suit Middle-Recent Pliocene formations (N22-3) represented by volcanic brecciae in blocks, tuff conglomerates, tuff sandstones, tuffs and tuffites of the middle and basic compositions. The Oceanic suit thickness is evaluated to be 900-1000 m. Sills, dykes and subvolcanic formations of various shape are associated with the Okhotsk and Oceanic suits volcanogenic rocks or break them. Mayak mountain located in Northern Kurilsk city is composed by sills. The rocks are represented by dense, massive, dark-grey diabases of paleotypic habit. Breaking bodies in the form of dykes have the age close to that of sills and thickness reaching the first dozens of meters. Subvolcanic bodies of Aerodromnoe Plateau type are of interest as the possible analogues of recent intrusions recharging the 1. , Northern Paramushir hydrothermal-magmatic system. Thick flows of andesite lavas occur on volcanogenic-sedimentary deposits of the Okhotsk and Oceanic suits. It has been determined that andesites are of Upper Pliocene age (Syvorotkin, Rusinova, 1989). The lava-pyroclastic deposits of basaltic composition supposedly being of Lower-Middle Pleistocene age are laid bare in the northern part of Paramushir island. The bipyroxene Interglacial andesites (Gorshkov, 1967) of the age beginning from 110 up to 20 thousand years are widely represented there. Bilibina, Krasheninnikova, Bogdanovicha, Ebeko et al.

volcanoes are composed by young post-Gl bipyroxene andesite lavas or andesite acial basaltic ones. The volcanoes form the large extensive tectonic-magmatic structure in the bowels of which andesite-basaltic melt migrated over a long period of time. Ebeko volcano located in the northern part of Paramushir is active. As is known it erupted in 1793, 1895, 1934-38, 1967-71 and 1987-91 yy. (Melekestsev et al., 1993; Menyailov et al., 1992). The last eruptions were phreatic.

Abyssal seismic sounding showed that in this area the thickness of consolidated earths crust is 20-25 km, the Mohorovii surface occurs at 20-25 km depth, the granitic layer thickness is 2 km and loose deposition thickness is 1-2 km. The negative anomaly of gravity is found in the area of Ebeko volcano central cone. It can be explained by low density of rocks forming the vertical cylindrical body with oval section ( 2 1 km). It is supposed that there is no large magmatic chamber directly under Ebeko volcano. The negative anomaly of gravity is explained by the foundation surface uplift in the form of arch having the negative excess density (Bernshtein et al., 1966).

The main water-bearing horizons and complexes are formed in accordance with the territorial geological (Belousov et al., 2002), Fig. 2. The water-bearing complex of Pleistocene-Holocene age is represented by andesites, andesite-basalts, their tuffs and brecciae, overlaying more than 80% of the territory. The water-bearing complex is a hydraulic system in which subsurface waters are contained in fissured volcanites enclosed among more massive and less flooded rocks. The high-discharge sources (up to 40-l/sec) are observed at effusion contacts with underlaying rocks, representing the bed outcrops extending up to 1 km distances. Single high-yield subsurface water discharges are localised in the tectonic deformations. Chloride-sulphate-carbonaceous waters with mineralization from 0,1 up to 0,3 g/l are predominant. The waters connected with the hydrothermally altered rock zones are characterised by sulphate-calcic composition, acid reaction and up to 2,9 g/l mineralization. The fumarolic thermae at the slopes of Ebeko and Neozhydanny recent volcanoes belong to this water-bearing complex. Water-bearing Rychagov S.N., Belousov V.I., Sugrobov V.M., Postnikov A.I. and Alekseev Yu.P.

complex of Pliocene age rocks is represented by the Oceanic suit rocks forming the gentle monocline with western 5-150 dip. The rock mass main peculiarity is wide development of loose rocks. Headless waters confined to the crust of weathering as well as horizons of head pressure strata-fissure waters are developed within the complex boundary. The complex upper part is recharged owing to atmospheric precipitation infiltration. To the great extent the complex water-bearing is conditioned by high jointing of rocks that suddenly decrease at the depth.

Figure 2: Hydrodinamic and morphotectonic map of the nothern end of the Paramushir Island (by E. Kalacheva, in edition by S. Rychagov). 1 Ground Water discharge zone. 2 Underground water feed zone. 3 Discharge zone of deep water-bearing horizons. 4 Suggested extension of discharge zone of deep water-bearing horizones. 5 Undeground water pressure zone. 6 Direction of undeground waters. 7 Direction of ground waters. 8 Sources: a thermal, b cold. 9 Boundaries of morphotectonic blocks Therefore two zones with different filtrational properties are distinguished along the vertical line. The upper zone (up to 100 m) has filtration coefficient 6-8 m/day and the lower one has that of 0,4 m/day. The spring discharges are not more than 1 l/sec. The water-bearing complex of volcanogenic-sedimentary Miocene age rocks is represented by the Okhotsk suit rocks. The complex depositions are characterised by great facies variability. Difference in jointing of rocks conditions layer after layer flooding of deposits and formation of fissure-strata pressure and non-pressure waters in them. Recharge is made owing to infiltration of atmospheric precipitation at the areas of rock outcrop to the day 1. , surface. The complex lower part suffers difficulties with water interchange. The water increased mineralization and relatively high quantity of Mg and Ca are explained by possible participation of shore thermae in their formation, described for the similar hydrogeological conditions (Kononov and Tkachenko, 1974).

The Northern Kuril deposit long-term geothermal resources are evaluated by two ways (Belousov et al., 2002): 1) according to natural heat discharge by the surface thermal manifestations; 2) according to the data on determination of thermal energy contained in mountain rocks saturated with the fluid. In the first case the long-term evaluation of geothermal resources is given taking into account the coefficient of the natural thermal capacity increase. At present the Northern Paramushir hydrothermal system thermal capacity can be evaluated approximately on the basis of determination of heat discharge by the surface thermal manifestations (Sugrobov, 1976; Sugrobov, 1995). Heat discharge made by the system eastern slope thermal manifestations is 10 850 - 14 300 kcal/sec. The quantity of heat discharged at the western slope is determined to be within the range 6 - 40 000 kcal/sec. The amount of heat discharge by the surface thermal anomalies is identified with the minimum geothermal resources. The coefficient values are determined through the comparison of operating reserves of the series of geothermal deposits with the thermal capacity of natural discharge of hydrothermae. For Kamchatka hydrothermal systems the coefficient of operating reserve increase varies from 3 to 7 in comparison with thermal capacity. The well water intake capacity increase can be explained by additional involvement of thermal waters during exploitation owing to the fluid flow from other horizons and removal of heat accumulated by the reservoir mountain rocks. If the capacity increase coefficient of the Northern Paramushir system is assumed to be 3 then the value of the long-term resources will be 43 000 kcal/sec that corresponds to 15 MW of electric capacity and 150 kg/s of water with 120-130 temperature.

The calculation of resources according to the heat accumulated in the block of mountain rocks within the estimated deposit boundary showed that their amount is greater as it is equivalent to 98 MW of electric capacity, the volumetric method of evaluation of the long-term resources is considered to be more reliable (Muffler, Cataldi, 1978).

Application of this method provides for assessment of the thermal energy contained in fluid-saturated mountain rocks. For this it is necessary to determine the volume of the block of heated mountain rocks (the geothermal reservoir), their temperature and specific heat content. When determining the reservoir volume its height can be assumed (before the exploring data have been received) by analogy with the studied typical systems to be 2,Rychagov S.N., Belousov V.I., Sugrobov V.M., Postnikov A.I. and Alekseev Yu.P.

km proceeding from the roof bedding at 0,5 km depth and the system basic depth of 3 km.

The area is calculated according to distribution of surface thermal manifestations taking into account peculiar features of the geological structure and hydrogeological conditions existing there (Sugrobov, 1995). The distance from Ebeko volcano thermal fields up to the first high-temperature wells is 5,5 km. If the estimated united hydrotherm flow width is assumed to be equal to the distance between the geothermal wells -1 -3 (about 1,km) then the reservoir area will be 10 km2. The area calculation error is 30%.

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