Silica Scaling Trial and Injection of Cold Separated Geothermal Water at Wairakei, New Zealand

Abstract

The depositional characteristics that might be associated with the injection of cold separated geothermal water (SGW) were investigated in a month long trial at the Wairakei geothermal field. This was achieved by passing 2000 m3 of aged and cooled SGW through a bed (250 mm diameter 4.2 m long pipe) packed with dacite chips 5-8 mm. No silica was deposited in the packed bed but less than 50 g of an iron and silica rich (32wt% and 33wt% respectively) scale deposited at the inlet screen. It is likely that the colloidal silica was flocculated by the iron corrosion product. Based on these positive results Contact Energy implemented an injection trial, with 200 t/hr of cold SGW injected into a cooler outfield sector west of the field, which successfully ran for 10 months.