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Abstract

From June 2008 to August 2013, slightly more than 67 kt of CO2 were injected at the Ketzin pilot site (Brandenburg, Germany). The CO2 reservoir is a saline aquifer at a depth of 630 – 650 m with initial pressure and temperature conditions of about 33 °C/62 bar. These reservoir conditions are near the critical point of pure CO2 (31.0 °C/73.8 bar) and the CO2 liquid-vapour equilibrium. In order to avoid phase transitions and near-critical phenomena throughout the injection process the CO2, which was delivered by road tankers and stored in intermediate storage tanks on site at ∼ -18 °C/21 bar, was pre-conditioned at site and pressurised to ∼ 65 bar and heated to ∼ 40 °C during regular operation. This injection process design worked exceptionally well. However, such a pre-conditioning and heating of the injected CO2 to elevated temperature is unrealistic for an industrial sized CO2 storage setting as the energy need is high and costly and the CO2 will be delivered by pipeline already at ambient temperature. To study the effects of lower pre-conditioning temperature and effects of potential two-phase flow on the injection process, a “cold injection” experiment was carried out between March and July 2013. The injection wellhead temperature was decreased stepwise from 40 °C down to 10 °C. Below 20 °C two-phase flow developed in the surface installations and in the injection well down to the reservoir and a mixture of gaseous and liquid CO2 has been injected. This two-phase CO2 injection ran smoothly for eight weeks without any operational issues.