| Title | BOREHOLE TESTING OF CALCITE DISPERSION AND DISSOLUTION CHEMICALS AT TAUHARA GEOTHERMAL FIELD, TAUPO, NEW ZEALAND |
|---|---|
| Authors | J. Seastres Jr., A. Dean, L. Miller, K. Barrie, M. Crisford |
| Year | 2015 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | dispersant, sequestrant, chelant, anti-scalant, inhibition, co-polymers, Tauhara Geothermal Field, calcite, scaling |
| Abstract | Sustainability of fluid supply to Tenon Drying Plant and Te Huka Binary Plant using three production wells located on the Tauhara Geothermal Field, Taupo, New Zealand has been hampered in the past by calcite scaling in the associated producing wells (TH06, TH14 and TH20). Two types of anti-scalant chemicals (GEO907 and GEO905) were trialled in these wells to inhibit wellbore calcite scale. GEO907, a co-polymer of polymaleic anhydrides (PMA) and polyacrylates (PAA) commonly used in geothermal wells, was initially tested. Calcium concentrations remained higher than baseline calcium (i.e. prior to chemical treatment) since anti-scalant dosing was commenced indicating successful calcite inhibition. Supporting well output tests, Tracer Flow Tests (TFT) and downhole surveys confirmed the successful inhibition of the depositing scale. Production well output has remained steady for 2-3 years (i.e. depending on the length of time the tubing was installed) since anti-scalant chemicals were used. GEO905, a combination of PMA and co-polymers alkyl ether polycarboxylic acid and sulfonates, was later tested due to its potential calcite dissolution properties particularly for wells partially blocked by calcite scales. In Tauhara, its effectiveness was primarily gauged in one well (TH20), which was not worked-over of calcite deposits before anti-scalant tubing was installed. The testing indicates that there could be a potential for calcite dissolution likely at higher dosing concentration (>30 ppm). The dosing rate needs to be much higher if further testing will be conducted as chelants are relatively slow in dissolving calcite scales compared to strong acids. |