Inverse modeling and forecasting for the exploitation of the Pauzhetsky geothermal field, Kamchatka, Russia Page: 3 of 30
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1. Introduction
The development of the Pauzhetsky geothermal field located in the Kamchatka Peninsula
of Far East Russia began in 1960. In 1966, a 5-MWe power plant was put into operation, which
was replaced in 2006 by a new 6-MWe unit. The first reservoir engineering studies of the field
(Piip, 1965; Sugrobov, 1970) revealed a liquid-dominated reservoir in layered tuffs at
temperatures of 170-190 C, with hot springs discharges at 31 kg/s. The first 10 years of
exploitation at a total mass rate of 160-190 kg/s showed a gradual temperature decline and
chloride dilution in the fluids produced by wells located near the natural discharge area.
Consequently, new exploration and development wells were drilled, and exploitation gradually
shifted away from the natural discharge area until fluid temperatures of 200-220 C were
reached. Production wells were drilled into a central upflow zone located 1.5-2.0 km southeast
of the old production field. The drop in temperatures and enthalpies continued, while the total
mass flow rate reached 220-260 kg/s between 1975 and 2006.
The forward TOUGH21 modeling study by Kiryukhin and Yampolsky (2004) had
difficulties in identifying and estimating the principal parameters of the geothermal system, and
in matching the large collection of data amassed during 36 years of exploitation. Thus, in this
study we employ iTOUGH22 inverse modeling to help verify the conceptual hydrogeological
model of the system, to identify key parameters, and to obtain more reliable parameter estimates
and subsequent predictions.
2. Conceptual hydrogeologic models
The Pauzhetsky geothermal system is situated within the Pauzhetka volcano-tectonic
depression of the Kamchatka Peninsula (Fig. 1). Figure 2 shows the well field, the footprint of
the presumed upflow zone as indicated by low electrical conductivity areas and surface
manifestations (hot springs, fumaroles, and hot ground areas with a temperature above 20 C at a
depth of 1 m), as well as a plan view of the computational mesh.
The hydrogeological model for the system is presented in Fig. 3 (see also Kiryukhin et al.,
2006). Cold meteoric water infiltrates to a depth of 5-6 km into a zone with temperatures above
250 C, where it heats up and begins flowing upward. The high-temperature ascending fluids,
with enthalpies of 950-1050 kJ/kg, reach the volcanogenic-sedimentary basin (consisting of N2-
1 TOUGH2 is a general-purpose numerical simulation program for multi-phase fluid and
heat flow in porous and fractured media. The simulator was developed in the Earth Sciences
Division of Lawrence Berkeley National Laboratory for applications in geothermal reservoir
engineering, nuclear waste disposal, unsaturated zone hydrology, environmental remediation,
and geologic storage of CO2. More information can be found at
http://www-esd.lbl.gov/TOUGH2.
2 iTOUGH2 (inverse TOUGH2) is a computer program that provides inverse modeling
capabilities for the TOUGH2 suite of simulators; it solves the inverse problem by automatically
calibrating a TOUGH2 model against observed data. Any TOUGH2 input parameter can be
estimated based on any observation for which a corresponding TOUGH2 output can be
calculated. An objective function measures the difference between the model calculation and the
observed data, and a minimization algorithm proposes new parameter sets that iteratively
improve the match. Once the best estimate parameter set is identified, iTOUGH2 performs an
extensive error analysis, which provides statistical information about residuals, estimation
uncertainties, and the ability to discriminate among model alternatives. Furthermore, an
uncertainty propagation analysis allows one to quantify prediction errors. More information can
be found at http://www-esd.lbl.gov/iTOUGH2.3
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Finsterle, Stefan; Kiryukhin, A.V.; Asaulova, N.P. & Finsterle, S. Inverse modeling and forecasting for the exploitation of the Pauzhetsky geothermal field, Kamchatka, Russia, article, April 1, 2008; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc894609/m1/3/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.