| Title | Evaluation of NaOH Injection in the Neutralization of Highly Acidic Cl-SO4 and SiO2-saturated Geothermal Fluids |
|---|---|
| Authors | Rhemal T. TAMBOBOY, Gabriel M. ARAGON, Mark H. REED |
| Year | 2015 |
| Conference | World Geothermal Congress |
| Keywords | Mt. Apo, acidic geothermal fluids, caustic injection, scaling, corrosion |
| Abstract | Some production wells in the Mt. Apo Geothermal Project in the Philippines have highly acidic, SO4¬-rich, silica-saturated fluid discharges. Downhole chemistry simulations using SOLVEQ-XPT show that the pH of the fluids is about 5 deep in the reservoir, but drops to 3.5-2.5 at shallow depths and in surface facilities. Monitoring of corrosion in these acid-discharging wells shows that corrosion rates are higher than acceptable for commercial well utilization of more than 25 years. One of the methods to reduce corrosion is to modify the chemistry of the acidic fluid by neutralization using a base such as NaOH, but this poses a risk of mineral scaling and wellbore blockage. Published studies of field tests conducted in other geothermal projects, however, showed that scaling can be minimized and that it is both a factor of geothermal fluid chemistry and process optimization. This study presents the results of the series of caustic injection side-stream tests conducted in one of the acidic geothermal wells in Mt. Apo, and discusses the mineral and fluid equilibrium changes with caustic addition using the titration model of CHIM-XPT geochemical software. Initial results showed that increasing the pH of a highly acidic SiO2-saturated geothermal fluid increases the risk of silica scaling due to the accelerated polymerization of silica and not due to reduced solubility. Further tests of operating parameters are recommended prior to downhole tests of caustic injection. |