| Abstract |
Development of geothermal energy has been restricted in Japan because approximately 80% of the abundant resources are located in national parks. To promote the energy diversification and utilize the resources in the national parks efficiently, an R&D (Research and Development) project funded by the Ministry of the Environment on geothermal well drilling technology is under way in Japan. The project purpose is to develop an environment-friendly low-cost drilling technology for a highly deviated well (2,500m deviation, 70° inclination) to access the hightemperature geothermal resources from the outside the national parks. The goal is to keep power generation cost asis, even if a highly deviated well is drilled. To achieve the goal, there are concrete targets of the project such as 10% drilling cost reduction and 50% productivity increase through technology developments, including cutting-edge technologies to increase ROP (Rate of penetration), optimal CSG design, logging and so on. For instance, to reduce the drilling costs by 10%, high performance motors and long lifetime high-speed rotation tri-cone bits were selected and tested. As a result, it was found that ROP increased by about 1.5 to 3 times compared with conventional techniques and that the system was very effective for difficult drilling conditions (hard formations, high temperature, a lot of LC (Lost Circulation)) in Japan. To achieve a 50% productivity increase, the optimal casing design is determined by comparing steam flow rates with drilling costs for different well deviations, using the GFLOW wellbore simulator. According to a case study in a geothermal field in Japan, it is found that the steam flow rate at the optimal casing design is about 1.7 times higher as compared with conventional wells, which are existing production wells drilled in outside of the national parks. The conventional wells are typically drilled down to around 2,000m deep whose averaged inclinations are 35deg. approximately and completed 8-1/2” diameter with 7” slotted liner. Further, a production logging tool, equipped with roller centralizers to evaluate the formation in a highly deviated well was newly introduced. The tool was applied to a well in Japan and successfully collected PTS (Pressure, Temperature and Spinner) data and fluid samples simultaneously. This paper outlines the detail of the project and the main R&D results. |