ACID STIMULATION OF KAWERAU INJECTION WELL PK4A USING HYDROFLUORIC ACID

Abstract

Injection well PK4a at the Kawerau Geothermal Field was acidised with 10% HCl / 5% HF in May 2017. This work, along with a program of several other acid well work-overs between 2016 and 2017, was conducted as part of a wider investigation to address silica management at Mercury’s geothermal fields, several of which have silica saturation indices in excess of 1.7, as described in Addison et al. (2015). Despite the use of various plant designs to reduce the risk of silica polymerization and deposition, injection well decline continues to be an issue.
PK4a was selected as a candidate well for acid stimulation, as it is known to suffer from injection decline that both modelling and laboratory testing supports being a result of silica scaling in the near wellbore formation. PK4a was acidised previously in 2010 also using 10% HCl / 5% HF, however the initial improvement in injectivity was short lived.
The 2017 PK4a acidisation program was optimised based on lessons learned from 2010 and from international case studies, in order to improve the chance of success. The results of this acid stimulation of PK4a are compared against the first acid stimulation of this well., as well the results of acid stimulations reported by other geothermal operators.