| Title | Current Status of the EGS Project for Water Injection in the Superheated Region at Okuaizu Geothermal Field in Japan |
|---|---|
| Authors | T. Okabe, M. Kato, T. Sato , Y. Abe, H. Asanuma |
| Year | 2016 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | EGS, R&D, JOGMEC, River water recharge, Recharge well, Superheated reservoir, Simulation, TOUGH2，MINC model, Okuaizu, Fukushima |
| Abstract | An R&D project funded by Japan Oil, Gas and Metals National Corporation (hereafter referred to JOGMEC) on technology development for geothermal reservoir evaluation and management is under way. The purpose of the project is to propose guidelines for a technical manual, based on numerical simulation and model verification, for better understanding of artificial water recharge effects to geothermal reservoirs and/or hot spring aquifers. Relevant examples include steam shortages resulting from the imbalance between the steam production rates and the natural water recharge; corrosion of surface facilities by superheated steam; and production of highly acidic fluid generated by superheating within the geothermal reservoir. These problems are widespread, and occur not only in existing geothermal power plants, but also in new geothermal developments and in newly developing areas. Our aim is to develop new and general countermeasures to such problems, which are both technically effective and cost effective. We will then collate these comprehensive measures into a new set of guidelines to ensure a stable supply of geothermal energy. Artificial water recharge is one of the EGS (Enhanced Geothermal Systems) technologies which has been successfully applied and shown to increase steam supply in the Geysers and Larderello geothermal fields. We will develop and verify an artificial water recharge technology through R&D set in the Okuaizu geothermal field in Fukushima prefecture, with an installed capacity of 65MW which has been running since 1995. The utilization factor of this power plant has reduced to 27.7% today, mainly due to the depletion of steam, the superheating effect, acidification and a decline of productivity and injectivity. The R&D project consists of project planning, design & management, survey and modeling, design and construction of a test facility, drilling of a recharge well, well testing and logging, a recharge test, numerical reservoir simulation, monitoring, and the preparation of a technical operation manual. There are very few examples of reservoir simulation of a superheated reservoir in the world. The location of the recharge well in the field was decided by the comprehensive analysis of simulations, risk evaluations from past field injection tests and tracer analysis. Drilling of the recharge well and, recharge testing started in the beginning of June 2015. Approximately 170,000t of river water was injected through to the end of December until a cyclic phenomenon at an adjacent well (Well-8) caused by the recharge operation was observed. Despite this cyclic behavior, an increase of steam flow at Well-8 of 3-5t/h and a reduction of non condensable gas (NCG) concentrations were benefits of the recharge operation. Effects at Well-5 and 6 located in the same fault of the recharge well were also observed suggesting it is possible to maintain and/or increase steam production and control NCG by suitable recharge operation. |