Long vertical sections challenge drilling efficiency

In the Mayacamas Mountains of northern California is a field of reservoirs with natural steam known as The Geysers. Metamorphosed sandstone, shale, and granite comprise the geothermal reservoirs of The Geysers, which reach temperatures of 600 degF.

To access this geothermal resource, the Northern California Power Agency (NCPA) conducts drilling to provide steam for its electrical generating facilities.

Because temperatures for this application range from 500 to 600 degF, wells are drilled using air to cool the bearings of open roller bearing bits instead of standard drilling mud. The 8 1/2-in roller cone bits being used for the application had an average drilling life of 30 to 35 hours before they were tripped out to avoid bearing failure and loss of cones. NCPA sought a more durable bit that would reduce trips and improve drilling performance.

Advanced bearing system materials answer HT application challenge

To increase NCPA's drilling performance, Smith Bits provided the 8 1/2-in SK47YAODR Kaldera HT roller cone bit. The bit's advanced bearing system materials enable it to endure the extreme heat that can break down standard bearing lubricants and compromise seals. This breakdown quickly erodes bearing functionality, leading to premature loss of roller cone performance and shortening bit life.

The Kaldera bit's increased bearing durability and longer bit life is the result of specially developed materials used in an advanced HT design:

• finite element analysis (FEA) optimized seal geometry and gland design
• robust grease reservoir system
• high-load capacity bearing design and materials
• computer numerically controlled (CNC) precision manufacturing tolerances.

Kaldera bit advances drilling performance

The 8 1/2-in Kaldera bit drilled for 49 hours from a depth in of 7,233 ft to 8,005 ft, enduring bottomhole temperatures that ranged from 500 to 600 degF. When compared with bits used to drill offset wells, the Kaldera bit drilled 14 hours longer and approximately 150 ft farther, representing a run length increase of 25%.