Lightweight cement slurries for carbon dioxide storage wells

MARTÍN, CHRISTIAN MARCELO

Berisso

Encuentro; DISCO2Store Mid-Term Meeting; 2022

Y-Tec

Lightweight cement pastes based on two classes of hollow glass microspheres (HGMS) under CO2 storage (CS) conditions were studied in this research. The changes induced to the microstructure of the cement pastes due to the presence of HGMS and to the exposure to CS conditions were measured in terms of mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and X-ray diffraction (XRD) with Rietveld phase quantification. HGMS appear to densify the cement matrix but confer an important amount of unconnected porosity to the composite material. Moreover, they accelerate the cement hydration and also react with the cement paste hydration products. The exposure to CS conditions severely affects the cement paste microstructure as cement hydration products (i.e. CH and CSH) react with the CO2 in a process called carbonation. After this exposure, the cement pastes show a coarser microstructure and a bigger porosity. The cement pastes with HGMS appear to be more affected by this mechanism.These microstructural changes affected the mechanical properties of the cement pastes. These were measured by unconfined compressive tests, triaxial tests and dynamic elastic parameters measured in unconfined and confined conditions. Given the unconnected porosity related to the presence of HGMS, the strength of cement pastes with HGMS showed a decreasing trend in all the mentioned mechanical parameters. This decrease was also related to the class of HGMS used, since each of them presented different strengths. Results for carbonated samples after the CS conditions exposure show that the change in the microstructure is related to an alteration of the overall mechanical behavior. Since the cement microstructure is becoming coarser/more disaggregate, when compared to not carbonated samples, the unconfined compressive strength is reduced but the confined strength increases.All these laboratory results are being used to model the behavior of the cement pastes under true carbon injection well conditions with a finite element method model called BIL. This model considers the coupled chemo-poro-mechanical problem for traditional cement pastes, in which an inert (to CS conditions) phase, CH, CSH and CaCO3 are considered, and the resulting compound material is homogenized for obtaining its mechanical parameters. HGMS were included into the model by updating the homogenization equations with those obtained in some previous research.