Benefits from the Utilization of a Calcium Carbonate Inhibition System for Production Wells at the Miravalles Geothermal Field

Abstract

The Miravalles Geothermal Field has been producing electric energy since March 1994. It has provided steam for Unit 1 (55 MWe) since 1994, a Wellhead Unit (5 MWe) installed in 1995, Unit 2 (55 MWe) in 1998, Unit 3 (29 MWe) in 2000, and Unit 5 (19 MWe, a binary plant) in the year 2004. During the first production tests of wells in the field, it was found that the reservoir fluids are over-saturated with respect to calcium carbonate at the flashing zone, causing deposition of this mineral and obstruction of the production casing within few days. A test conducted in 1989 proved that systematic chemical inhibition inside the production wells could prevent the formation of calcite scale. All the inhibitors tested in the field are described in this article. Since 1994, the inhibition system has been used successfully in the production wells that supply steam to the generating Units. Experience has indicated that the injection of an appropriate dose of inhibitor makes it possible to produce the geothermal wells with little or no deposition of calcium carbonate, and it is less expensive than performing mechanical cleanouts.