Résumé
Using a combination of core flooding experiments and wettability measurements, we evaluate the sealingefficiency of Heletz caprock under CO2 sequestration conditions. The flow through experiments consisted offlowing CO2 enriched fluid into two micro-fractured cylindrical cores (15 mm length - 9 mm diameter, withhydraulic aperture: 2.7 µm for the sample named H18A and 13 µm for sample named H18B) and monitoring thepermeability changes, the evolution of the chemistry from the inlet and outlet fluid. The changes in microstructuresand mineralogy were also studied using an environmental scanning electrons microscope (ESEM) and X-raymicro-tomography (XRMT) images.The fracture permeability was found to decrease significantly in the two experiments from 14.1×10-12 m2 to5.0×10-12 m2 for experiment H18B and from 6.5×10-13 m2 to 2.8×10-13 m2 for experiment H18A. Calcitedissolution and reconversion of k-feldspar to illite and kaolinite were the main reaction on sample H18B while“calcite precipitation” in batch condition was the dominant reaction on sample H18A. Accordingly, the decreasein permeability was induced by the dispersion of dissolution products and the re-organization of clay particleswithin the fracture for sample H18B as shown by micro-tomography and ESEM images. The fracture healing dueto the calcite and clay mineral precipitation along the fracture was attested by ESEM image for sample H18A.The results of capillary pressure breakthrough calculated by applying the Washburn equation and the reservoirscaling method from intrusion of mercury are approximately 380 kPa and 310 kPa for H18B and H18A respectively. Although, these values are sensibly different but close to each other and in good agreement to indicate theweak storage capacity of the heletz caprock. Subsequently less than 90 m of CO2 column height can be efficientlystored in the Heletz reservoir. Thus the self-mitigation of the CO2 leakage is expected only when few quantity ofCO2 will be injected.