The PUNA Geothermal Venture (PGV) wells are located on the Big Island of Hawaii near the Kilauea Volcano. This results in a highly fractured, hard, hot formation, challenging PGV with lost circulation, hole-cleaning, cooling, and stuck pipe issues. With static formation temperatures of 600°F the traditional fluid system incorporates water-based mud, various cooling systems to maintain operation temperature limits < 300°F, micronized cellulose for lost circulation, and mud-pulse measurement while drilling.

Although aerated mud is the preferred drilling fluid for operations performed in areas prone to lost circulation, there are certainly drawbacks and considerations to running aerated fluids.

1. One of the industry standards, mud pulse telemetry better known as Measurement While Drilling (MWD), will not function in aerated fluid.
2. Reduced fluid density hampers the ability to lift cuttings.
3. Aerated fluid adversely affects the ability to power positive displacement mud motors.
4. The thermal capacity of aerated mud is lower, reducing the cooling effect on the hole.
5. Drilling equipment exposed to the high velocities can be quickly eroded.
6. The reduced hydrostatic head can have a detrimental effect on wellbore stability.

PGV along with its contractors managed to complete the 26" hole section flawlessly on aerated mud, which has not been part
of the standard program. The following techniques were used:

1. A pump rate of 350 GPM
2. Foaming agents supplemented with polymers were used to provide rheological properties and gel strengths to facilitate hole cleaning
3. A polymer was used for cuttings encapsulation and lubricity.
4. A controlled rate of penetration (ROP) was employed to allow for proper cuttings disposal and hole cooling
5 . A 9½" performance mud motor equipped with high-temp stator elastomers, provided high torque drilling with temperature resilience.
6. Fixed hole openers were used to further ream and condition the borehole.

This section of the well was drilled successfully and 22" casing was landed with no problems . This is a significant improvement as compared to other offset wells in the area.