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 rocks and carbonate 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. 800 m by a sampler (500 ml 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 site 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.