Analytical Sciences

Colorimetric pH Measurement of Pressurized Groundwater Containing CO₂

Saeko MITO,* Kei OKAMURA,** and Hideshi KIMOTO***

*Research Institute of Innovative Technology for the Earth (RITE), 9-2 Kizugawadai, Kizugawa, Kyoto 619-0292, Japan
**Center for Advanced Marine Core Research, Kochi University, B200 Monobe, Nankoku, Kochi 783-8502, Japan
***Kimoto Electric Co. Ltd., 3-1 Funahashi, Ten-noji, Osaka 543-0024, Japan

A gas-tight pH measurement is needed to monitor water chemistry at a CO₂ geological storage site. In the CO₂ reservoirs, the temperature and pressure are generally more than the critical point of CO₂ (31.2°C and 7.38 MPa). In this study, a colorimetric pH measurement method was examined up to 20 MPa for future application to various CO₂ reservoirs. A mixture of two color indicators, bromocresol green (BCG) and metacresol purple (mCP), was considered to be a suitable measurement method between pH 3 and 9. The uncertainty up to 20 MPa was less than 0.12 pH units without any correction of pressure effects. We demonstrated a pH measurement of formation water at the Nagaoka CO₂ post-injection site. The pH measurement was successfully accomplished under a high-pressure condition (ca. 11 MPa) and without degassing of CO₂.

J-STAGE: View this article in J-STAGE