Fluid-rock interactions during intermittent injection of supercritical CO2: An investigation for CO2 storage in the depleted Nini West oil field, Danish North Sea.

• During injection of 5 cycles of scCO 2 /brine, no change in injectivity was observed. • The main minerals of the glauconitic sandstone, i.e. glauconite, quartz and feldspar seems to be unaffected mineralogically by cyclic injection of scCO 2. • Measured initial brine permeabilities are in average 81 % of measured N 2 permeabilities. • Effective ScCO 2 permeability measured between 22 and 38 % of the initial brine permeability. • The low viscosity ratio of scCO 2 to brine (µ CO2 /µ brine = 0.1) resulted in poor displacement of brine by scCO 2 , resulting in high residual water saturation after number of scCO 2 flooding. CO 2 that is planned to be stored in the depleted Nini West oil field will be delivered by ship which results in intermittent injection of supercritical CO 2 (scCO 2). It is important to investigate the effect of this injection scenario on rock specimens in the early phase of the storage program. In this regard, core flooding experiments have been conducted at current reservoir conditions of 200 bar and 60 °C. The state of plug samples pre- and post-scCO 2 injection were compared by coupled scanning with the scanning electron microscope (SEM) and micro-CT scanning to track mineralogical changes at core-scale. The coupled approach shows partial dissolution of garnet, specifically almandine and carbonate minerals such as siderite, rhodochrosite and calcite in the glauconitic sandstone after 5 sets of scCO 2 injection periods. Effluent brine ion content measured after each brine injection operation shows an increase in Fe tot , Si + , and Mn 2+ in the effluent brine compared with the injection brine, which agrees with dissolution of minerals captured by the SEM and micro-CT scan. ScCO 2 effective permeability at the end of each scCO 2 injection period ranges between 18 and 34 % of the initial brine permeability at 100 % water saturation (S w). The conclusion is that CO 2 permeability over these periods of injection is not affected by neither the dissolution of minerals, since these minerals are present only in low concentrations, nor the salt precipitation due to scCO 2 injection. [ABSTRACT FROM AUTHOR]

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