The PUNA Geothermal Venture wells are located on the Big Island of Hawaii. The project site is close to the Kilauea Volcano with a high geothermal gradient resulting in static bottom hole temperatures above 600˚F. As with most geothermal projects, lost circulation can be a problem in drilling these wells, as it is costly, resulting in drilling delays, hole instability and stuck pipe. These associated drilling problems can ultimately jeopardize the hole. By controlling mud losses, the amount of time combating lost
circulation is reduced, providing a more stable wellbore. Controlling mud losses has also been helpful with logistics since Hawaii is 2,000 miles away from the closest drilling infrastructure. The drilling, as with most geothermal wells, is conducted with unweighted drilling mud containing few solids to bridge the formation and limit fluid losses. To minimize lost circulation when drilling the intermediate hole intervals, micronized cellulose material is introduced into the mud system, which stops lost circulation and/or reduces mud losses to seepage. This ability to control mud losses in the intermediate sections provides improved wellbore conditions for directional drilling and benefits cementing operations. To minimize losses and protect the reservoir, the production interval is drilled with a high-temperature copolymer drilling fluid conditioned with micronized cellulose. The micronized cellulose material being used is a unique fibrous material that has been developed for controlling seepage and lost circulation while drilling depleted, fractured or other permeable zones. This paper will discuss the drilling operation, drilling fluid and the application of micronized cellulose on these geothermal wells.