Puna Geothermal Venture
Well Name: Kapoho State-11RD (Geothermal Well)

Tests and surveys on the Kapoho State-11RD, a geothermal well near Hilo on the island of Hawaii, indicated a shallow leak into the formation zone. Injection fluid was traveling through the current fractures from the re-drill to the original wellbore, creating interference problems with the production zone of another well. Re-drilling was considered, but the decision was made difficult by previous re-drilling and workovers to the well, and the proximity of any new bore to the previous bores.

A coordinated research effort involving Baker Hughes Integrated Services and the client, Ormat, revealed that the most economical procedure would be to relocate the target and kick-off point, sidetrack the well by performing a casing exit through the two casing strings to increase the separation from any previous wellbores, and then directional drill the hole to the designated target.

A window was milled in 37½ hrs, including drilling 15 ft of formation below an extra long whipstock ramp that was more than 19 ft long. The PDC mills cutting structure allowed milling with lighter weight, which enabled the mill to stay on the face of the whipstock and avoid departing from the ramp prematurely.

Even though the T-95 and T-90 casing grades usually require several runs to mill a window through two strings, and drilling with a PDC formation window mill is also difficult, the window was successfully milled. When running the drilling bottomhole assembly (BHA) through the window, no drag was encountered. The 7-in. casing was also run through without drag and then cemented.

The 5⅞-in. productive interval was drilled 120 ft when it was discovered that the 7-in. liner cement job was fatally flawed, and this entire interval was abandoned.

A second window was milled several hundred feet above the first, through the same two strings of casing, using the same equipment and methods. This window was similarly successfully milled in 30½ hrs. The 8½-in. hole was drilled, and the 7-in. liner was run and cemented. The 6¼-in. productive interval of this sidetrack was successful in encountering the top of production at 5,135 ft and was drilled to 6,872 ft, where pipe was inadvertently stuck in the hole. It was completed with 4.5-in. preperforated liner from 4,755 to 4,755 ft and a combination 7-in. and 5-in. alloy injection hang down string from surface to 3,038 ft.

Job success was attributed to a team effort involving Ormat, Geothermal Resources Group and Baker Hughes Integrated Services. Coordination included the engineering, technical advice and field support services to achieve this task. This paper describes the well condition, the project plan, the equipment/materials used, and the procedure.