Scale Precipitation during Circulation of the Hijiori HDR Site, YAMAGATA, JAPAN

Several kinds of scale precipitated in the pipeline and production well during a two-year circulation test in the Hijiori HDR system in Yamagata Prefecture, Japan. Amorphous silica and calcium carbonate scale tended to precipitate in the flow line, with the ratio of silica and calcium carbonate depending on fluid temperature and chemical composition. In the case of well HDR-2, located closer to the injection well, the flowing wellhead temperature was about 120 deg C and the major scale was calcium carbonate, with a precipitation rate of 13mm/month. However, in the case of well HDR-3, located further from the injection well, the wellhead temperature is about 160 deg C and there was a slight precipitation of amorphous silica scale. Anhydrite scale precipitated at the highest temperature zones in the deep part of the production wells because anhydrite has a reverse solubility curve and the fluid has a rich anhydrite composition dissolved from the rock of the deep reservoir.