| Title | CHEMICAL REMOVAL OF FORMATION SCALE IN GEOTHERMAL PRODUCTION WELLS |
|---|---|
| Authors | K. McLean, D. Wilson, L. Muller and M. Bluemle |
| Year | 2021 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Geothermal production well, formation scale, chemical cleaning, well recovery, stimulation |
| Abstract | It is common for geothermal production wells to suffer from scaling while in operation, which can drastically decrease or halt production. The scale is usually calcite and can also contain silica which makes the scale harder and more difficult to remove. In reservoirs with significant silica in the fluids, the loss of production can be due to silica as much as calcite. In high enthalpy production wells flashing and scaling occur in the formation, and this is a much more difficult challenge than scaling in the wellbore, as formation scale can only be accessed with chemicals and not mechanical methods. Traditional chemical methods of trying to recover such wells use hydrochloric acid (HCl), and whilst this impacts calcite, silica and silica-based deposits are not soluble in HCl. Some companies have tried using mud acid applied through a coil tubing unit. However, there are significant risks involved due to the strength and aggressiveness of the acids (corrosion, human and environmental risks), and results have been varied, so this approach has mostly been abandoned. A partnership between Contact Energy, Solenis and Thermal Clean Ltd has developed and successfully applied new technologies to chemically clean formation scale in production wells using a combination of acid and caustic to remove both calcite and silica. This is the only viable method to recover production well formation scaling and has been successful in restoring dead production wells to 100% of maximum historical capacity. There are also indications the method could be a stimulation technique, dissolving formation minerals rather than just scale. Examples are given from New Zealand and Mexico. |