Aerated Geothermal Drilling Design

Project Objectives

Primary objective of this aerated geothermal drilling project was to determine operational fluid and air rates for drilling a geothermal steam and brine reservoir at temperatures of 620 deg F. Determining liquid and air rates to optimize hole cleaning and wellbore pressures whilst drilling through the reservoir steam cap and the brine zone.

Project Description

Drilling geothermal steam reservoirs often require drilling with a mixture of water and air to control the wellbore pressures. Geothermal steam reservoirs are often sub hydrostatic (low pressure) fractured reservoirs at extremely high temperatures (300 to 370 deg C).
Drilling with only water often results in total losses into the fractures. As the fluid level drops in the wellbore steam zone can flow into the well, resulting in steam kicks. Using LCM or cement to control losses is not possible in the large fractures. Using aerated fluid allows returns to be controlled and losses to be minimized.
Similar to underbalanced drilling operations multiphase modeling is completed to determine wellbore pressures, velocities and injection pressures. But wellbore pressures remain above the pore pressures. This modeling allows the drilling program to be completed with liquid and air flow rates and expected pressures. Once that is completed the detailed drilling procedures are completed in readiness for the drilling operations.

The client was able to optimize geothermal drilling parameters and complete the detailed drilling program and drilling procedures.