Successfully Applying Micronized Cellulose to Minimize Lost Circulation on the PUNA Geothermal Venture Wells
Abstract
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.
Introduction
The Puna Geothermal Venture (PGV) facility, in operation since 1993, is the first and only commercial scale geothermal plant in Hawaii. It currently produces about 30 MW of power with the reservoir’s estimated potential between 500 to 700 MWe. The production wells supply geothermal water to the turbines; then the water is re-injected, resulting in power generation with zero emissions.
PGV is located in the Puna District at Kilauea Volcano’s East Rift Zone. Kilauea is an active volcano in the southeastern part of the island of Hawaii. The geothermal gradient on these wells is approximately 7°F per 100 feet; a temperature profile of a typical well is listed in Table 1:
Lost circulation can occur from surface to total depth. Hole stability and hydrogen sulfide are concerns and have been encountered as a result of lost circulation and during workover operations. Drilling large-diameter holes require good drilling practices to ensure adequate hole cleaning and to avoid lost circulation. Minimizing mud losses and special techniques facilitate high-quality cement jobs. This project requires directional drilling in the intermediate intervals to reach the production targets. Large drilling fluid surface volumes, good drilling practices and mud cooling equipment are required to facilitate an efficient operation.
DOWNLOAD PDF (738.5 KB)