Commercial Production of Acid Wells at the Miravalles Geothermal Field, Costa Rica

Abstract

The Miravalles Geothermal Field reservoir fluids typically have a neutral composition, but four of the wells intended for future production produce acid fluids. This has required studies to determine the feasibility of neutralizing the acid fluids and using the wells in a safe manner. In 1996 the first practical test of neutralization in well PGM-19 was conducted. Sodium hydroxide at 50% (NaOH, 1+1) was injected at 950 m depth to neutralize the acid fluid. The neutralization system developed raised the surface pH values from 2.5 to around 6.5 and maintained it stable over the test period of 28 days. The results show that the neutralization system is successful. The estimated costs of the system implementation are around $167,000 and the investment would be recovered in about 17 days, according to the well potential. Well PGM-19 is projected to start production in late January of 2000.