Experimental study of CO2 injection in a simulated injection well: the MIRAGES experiment

The MIRAGES experiment mimics an injection well at the lab scale (1/20). This experiment allows the injection of supercritical CO2 under geological conditions of pressure and temperature. The injection flow rate, confinement and injection pressures and temperatures are recorded during the 30 days of the experiment. Chemical parameters (pH, major element contents) are also monitored. The reservoir is represented by a core sampled in the formation of Lavoux limestone. The core is drilled to form an injection well in which an injection tube (made of stainless steel) is sealed with class G Portland cement together with two discs of Callovo-Oxfordian clay representing the caprock. After the experiment, the core sample is studied to follow the petrophysical changes of the well materials and rocks. The interfaces between the reservoir, caprock, cement, and steel are investigated using scanning electron microscopy, cathodoluminescence, and Raman spectrometry. The main results suggest (i) good cohesion of the different interfaces despite the carbonation of the cement, (ii) the precipitation of different carbonate phases relating the changes in the chemistry of solution as a function of time, (iii) the enrichment in silica of the cement phase subjected to the action of CO2 providing evidence of new mechanisms of in situ silica re-condensation, and (iv) the very good mechanical and chemical behavior of the caprock clay despite the alkaline flux from the cement and the acidic attack from the dissolved CO2.