Evaluation of Naoh Injection into Acid Wells of Leyte Geothermal Production Field and Mindanao 1 Geothermal Project: The Case of MGSD and KN2D Wells

Abstract

This paper focuses on the role of the pKa of HSO;/SO4 buffer and its effect on NaOH injection. The pKa dictates the bufferÆs maximum effectiveness to resist large changes in pH when an acid or base is added, or when the solution is diluted. To be able to break away from the maximum effectiveness of the buffer, resulting pH of the mixture must be higher than the pKa at certain injection temperature and depth.

The results of the study revealed the most likely depths of injection for the acidic wells MGSD and KN2D. In MGSD, these depths range from 950 to 1253 mMD at 0.9 to 1.0% mix of 0.25m NaOH. At these depths, pH of the NaOH mix is higher than the pKa. In KN20, a greater range of depths is plausible. Injection can be set at the well head or at the maximum depth of 2100 mMD. At the well head, 0.1 to 1.0% of 0.25m NaOH mix can also overcome the HSOJSOt- buffer. At ZlOOmMD, 0.7 to 1.0% of 0.25m NaOH mix can also can overcome the buffer. The wide range of injection depths at KN2D compared with MGSD can be related to the closeness of its initial brineÆs pH values to the pKaÆs.