Practical Application of Directional Drilling at Takigami Geothermal Fields, Japan

Abstract

For the geothermal energy, directional drilling is an important method that needs to be explored and developed. In geothermal fields of Japan and in many wells of Takigami field, 90% of production and re-injection wells are completed by the directional drilling. Some directional wells of reinjection site No.2 are drilled for the same E-W fault from an early period of exploration to a developmental and an operational periods. In order to compare the conventional directional drilling with the advanced drilling system, this paper reports the optimization of these wells' trajectory, casing program, drilling progress and drilling cost.
At Takigami, starting from 1987, new directional survey system, Measurement While Drilling (MWD), was used for the production wells. After 1994, ten reinjection wells were drilled by the advanced drilling system ("The steerable drilling", MWD and High-torque Steerable Downhole motor). In the case studies of these wells, the steerable drilling system was an effective measure for drilling a pinpoint target where the well trajectory (drilling target) was required to be accurate. This made the process easy. Another benefit of the steerable drilling is that it allows to reduce the survey time, trip time and shorten drilling progress by many days. High-torque Steerable Downhole motor produce the penetration rate 2-3 times faster than the conventional directional drilling. The latest steerable directional well TR-7 can reduce drilling progress by half (or less) and drilling cost by 30% compared to that of TT-22.
Capacity of reinjection wells in Takigami was depleted by a silica scaling. The reasons for depletion are studied by silica scale and reservoir simulator. The steerable drilling contributed to a sidetrack of the existing well in order to rebirth reinjection capacity of the well. TR-3S (sidetrack well of TR-3) was drilled for 13 days. By steerable drilling, the cost was reduced by 20% of the new well.