CASE STUDY: ONLINE GEOTHERMAL WELL STIMULATION AND SILICA-BASED FORMATION SCALE REMOVAL

Abstract

Silica remains one of the prominent problems that cause the loss of capacity in geothermal reinjection systems. Until recently, no solutions were available to stimulate or completely recover reinjection capacity if the formation beyond the wellbore was scaled with silica or silicon-based deposits.
Historically, in New Zealand, hydrofluoric acid (HF) or mud acid was used to try to improve and recover reinjection well capacity; however, the risk to the assets, the cost of the application, the risk to the environment, and the risk posed to the people doing the job did not warrant the short-term and marginal results achieved using the HF intervention.
Recently, an application approach and chemistries that often enable geothermal operators to recover the full capacity of their reinjection systems were developed. This new technique has many advantages over traditional methods. Advantages include avoiding the need to shut down the well; reducing cleaning time to two days during full and normal operation; using far lower concentrations of chemicals; and recovering,
in many cases, well capacity that exceeds 100% of the full historical capacity.
One of the world’s leading geothermal operators invested significant resources into the understanding of this new method and thus has been able to contribute to the collaborative advancement of this technique to the wider geothermal industry.
This paper documents three case histories using this new online well stimulation process and includes a comparison with offline cleans using HF. The geothermal company reviewed the two methods and found that the online method was at a minimum 13 times better in terms of ROI and benefits than offline techniques.