Case Study of Calcium Carbonate Scale at EGS and Hot Spring Binary System

Abstract

Calcium carbonate is one of major scale in geothermal system. Not only conventional system but in new concept geothermal system, EGS and hot spring binary systems calcium carbonate scale precipitate in well, pipeline and heat exchanger. For example, at Hijiori EGS test site, calcium carbonate scale on pipeline of HDR-2 rapid increased after thermal breakthrough of reservoir. To decrease scaling, we try to inject scale inhibitor from injection well HDR-1 and about 20% scale decreased with 20 ppm inhibitor.In other case, at Otari hot spring, calcium carbonate precipitate not only on hot spring water path due to degas from fluid but on cooling water path due to increasing temperature. Recently, many hot spring sites introduce small binary system but they face to the problem of scaling including calcium carbonate. Then, we estimate scaling possibility and develop the scale preventing method, for example, electrode method besides scale inhibitor.