抄録
Directional drilling is an important technology to explore and develop for geothermal energy and many geothermal wells are completed by directional drilling at Takigami geothermal field. Especially, many directional wells of the No. 2 reinjection site are drilled for the E.W fault from an early stage of exploration to a development and an operation stage. This paper reports the optimization of well casing program and directional drilling technique based on geological and drilling data analysis of each stage. At Takigami geothermal field, the conventional directional drilling technique (a combination of magnetic single shot survey and Low-torque Down Hole Motor) was applied for directional wells in exploration stage before 1990. On the other hands, the steerable drilling technique (a combination of MWD and High-torque Steerable Down Hole Motor) became widespread in geothermal fields after 1994 and this technique was applied for directional wells during a development and an operation stage. The steerable drilling produces an accurate directional control of a well trajectory and a long deviated directional well. Moreover, the steerable drilling shortens drilling progress by reducing directional survey time and increasing penetration rate in comparison with the conventional directional drilling. Finally, the cost reduction of drilling operation is achieved by the steerable drilling at Takigami geothermal field.
