長期循環試験，第1期の数値シミュレーション結果から推定される肘折貯留層の生産特性について

－多層貯留層を用いた高温岩体発電システムの開発に関する研究(第1報)－

抄録

Since 1986, a Hot Dry Rock (HDR) geothermal energy R&D project has been carried out at Hijiori in Yamagata Prefecture, Japan. At present, the Hijiori HDR system has two reservoirs (a shallow reservoir and a deep reservoir) and four wells (SKG-2, HDR-1, HDR-2a and HDR-3) completed in high temperature granite at the site. Injection well SKG-2 was completed in the shallow reservoir formed at a depth of about 1,800 m. Injection well HDR-1 was completed in the deep reservoir, which is located at a depth of about 2,200 m. Both reservoirs were intercepted by the production wells HDR-2a and HDR-3.
From November 27, 2000 to November 15, 2001, the Long-Term Circulation Test (LTCT), Term 1 was conducted with HDR-1 as an injection well, and HDR-2a and HDR-3 as production wells. Two important changes were noted during this test: 1) wellhead temperature at HDR-2a decreased from about 175 °C to about 110 °C ; and 2) pressure in the shallow reservoir increased toward the end of the test. These data are used to evaluate the lifetime of the deep reservoir and to assess the evolution of the multi-reservoir system during the test.
A simple multi-reservoir model was developed and the test data simulated using the FEHM (Finite Element Heat and Mass transfer) code developed at Los Alamos National Laboratory. The two most important conclusions of the modeling are: 1) the production wells produce more fluid from the shallow reservoir than from the deep reservoir; and 2) permeability of the deep reservoir increased during this test.