Review of chemical cleaning methods in geothermal wells

Abstract

We have reviewed technologies and techniques applied to geothermal well cleaning to recover lost productivity from wells using chemical cleaning methods. We have undertaken a review of the publicly available literature on geothermal well cleaning and adjacent technologies in the petroleum industry. Whilst many hypothetical solutions are proposed in laboratory-based studies, we found that the predominance of real-world applications is limited to the use of simple Hydrochloric (HCl) and Hydrofluoric (HF) acid blends.
Acid treatments are usually accompanied by mechanical cleaning operations using drilling rigs and coiled tubing units as part of well intervention programmes. To decouple pure chemical cleaning from mechanical cleaning is difficult as the combined effects are intended to achieve more than a pure chemical or pure mechanical treatment alone.
The predominant use of HCl and HF acids for chemical cleaning is likely due to the availability of these chemicals, the cost of transport and the relatively well-known and understood reactions that take place between scale materials and these acids. On reviewing more than 112 well workover examples, 89 of these cases used a blend of HCl/HF. The rest of the wells were cleaned using blends of either Sodium Hydroxide (NaOH), Formic Acid, proprietary organic acids, condensate waters, or acetic acids.
As a corollary, the global petroleum well cleaning industry is also dominated by the use of HCl/HF acids for cleaning scale and stimulating production formations, even though many proprietary acid blends are offered through service providers; we found no evidence that exotic chemical blends have achieved significant uptake in cleaning geothermal wells.