Advanced Research for CO2 Fixation in Geothermal Field


This research was carried out conducted by Research Institute of Innovative Technology for the Earth (RITE), Central Research Institute of Electric Power Industry and Mitsubishi Materials Corporation, and was entrusted from New Energy and Industrial Technology Development Organization (NEDO).

1. Purpose

Reaction rate of CO2 and some mineral increases and solubility of carbonate minerals decreases under high temperature condition. In the case of CO2 storage into geothermal field, CO2 fixation as carbonate minerals is expected. Once carbonate minerals precipitate forming a sealing layer, CO2 storage will be possible under the sealing layer. Then this study is carried out to estimate the possibility of CO2 storage technology into geothermal filed.

Concept of CO2 fixation system

Concept of CO2 fixation system

2. Results

Assessment of CO2 storage capacity and cost in geothermal field

We discussed the possibility and application of the CO2 fixation system in Japan. To assess the practical use, we selected the geothermal areas excluding the national park area and main CO2 generate facilities (thermal power plants and cement factories) 20km or more away. Several geothermal areas for practical use exist in Hokuriku and Kyusyu area of Japan. Total capacity of CO2 storage was estimated at 1.18 billion tons CO2 on the basis of assumed rock porosities (average: 4%) and the solubility of CO2 (3 wt%). The cost was evaluated at 5136 yen/ton- CO2 in the case of storage rate of 1 million tons CO2 per year and transport distance of 20km.

Laboratory experiment of CO2-water-rock interaction under hydrothermal conditions

CO2-water-rock interaction under hydrothermal conditions was investigated by the batch and column tests. The mineral and rock samples were plagioclase (labradorite) and granodiorite in Ogachi geothermal field, respectively. In the case of experimental with plagioclase, it was clarified that Ca and Si are released from the rock surface by CO2-water-rock interaction. In the case of experimental with granodiorite, it was observed that anhydrite, mica and chlorite dissolved followed by precipitation of AlO (OH) and goethite on the rock surface.

Field experiment in Ogachi geothermal field

Field experiments were performed to investigate CO2-water-rock interaction in Ogachi geothermal field. CO2 dissolve water (4.3 wt%) was injected into the bored hole and granodiorite (Ogachi rock) was soaked. The temperature was 208 °C, and soaking time were 16.5 hours. After the soaking, the dissolution of anhydrite was observed as well as the laboratory experiment.

Simulations of CO2-water-rock interaction under hydrothermal conditions

Laboratory and field experiments were simulated by geochemical code. The results indicated that plagioclase (anorthite) will dissolve and calcite, clay minerals (kaolinite) will precipitate subsequently. Then sealing layer will form as a result of CO2 fixation.

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