Laboratory and Field Tests of CO2–water Injection into the Ogachi Hot Dry Rock Site, Japan

This paper reports the results of laboratory and field experiments of CO2 sequestration into the Ogachi hot dry rock(HDR; the temperature is 200 degree C) site, where a part of CO2 will be expected to be fixed as carbonates by interaction with rocks (Georeactor; Ca extraction from rock and carbonated fixation). In 2007, CO2 dissolved water (river water with dry ice) was directly injected into OGC-2 (from September 2nd to 9th) and Run #2(from September 11th to 16th). Several tracers were also injected at the same time. Water samples are collected at the depth of ca. 800m by a sampler (500ml in volume) and monitored for their chemical and isotopic compositions. During the Run #2 experiment, river water was injected into OGC-1 at 2 days after injection of CO2 water into OGC-2.During the field experiments, dissolution or precipitation rates of calcite were determined by using a technique of "in situ analyses". Calcite crystals covered with Ti rod or Au film is hold in a crystal cell and set in a crystal sonde. The crystal sonde is then put into OGC-2 and water samples at the certain depth is introduced into the sonde. After 1 hour, the sonde is recovered and the calcite crystal is observed by a newly developed phase shift interferometer to analyze the dissolution or precipitation rates of calcite from the reservoir fluids. The "in situ analyses" show that calcite precipitation was observed within 2 day after the injection. This supports the view that most of CO2 injected might be fixed as carbonate. (C) 2009 Elsevier Ltd. All rights reserved