Does Injected CO2 Affect (Chemical) Reservoir System Integrity? - A Comprehensive Experimental Approach

Abstract

In order to investigate and characterize single fluid-mineral interactions we successfully implemented a new hydrothermal laboratory. CO2-exposure experiments using separates of rock-forming minerals were performed on a hydrothermal rocking autoclave. The system is equipped with flexible Titanium cells allowing for isobaric sampling. Experiments were run for one week at 80°C and 20 MPa/30 MPa. Rietveld refined XRD data reveal that the initial siderite separate is composed of 69.6±1.3 wt% siderite, 26.7±1.2 wt% ankerite and 3.8±0.8 wt% quartz, respectively. 0ver time, siderite abundances increase and ankerite abundances correspondingly decrease, while quartz abundances are constant within error. Fluid data show rapid increases for Ca2+, Mg2+, Mn2+ and Fe2+. After these rapid increases, Ca2+ and Mg2+ reveal slight decreases that are followed by subsequent rises to maximum concentrations at the end of the experiments, while Mn2+ and Fe2+ decrease continuously after the initial maxima. SEM micrographs of CO2-exposed samples indicate dissolution of ankerite, while siderite and quartz are mainly unaffected. The experiments on the siderite separate clearly show that ankerite is dissolved and siderite is stable. We conclude that siderite is a potential CO2 trapping phase in iron-bearing reservoirs.