Incorporating Nanoscale Effects into a Continuum-Scale Reactive Transport Model for CO₂-Deteriorated Cement

Abstract

Wellbore cement deterioration is critical for wellbore integrity and the safety of CO storage in geologic formations. Our previous experimental work highlighted the importance of the portlandite (CH)-depleted zone and the surface dissolution zone in the CO-attacked cement. In this study, we simulated numerically the evolution of the CH-depleted zone and the dissolution of the cement surfaces utilizing a reduced-dimension (1D) reactive transport model. The approach shows that three nanoscale effects are important and had to be incorporated in a continuum-scale model to capture experimental observations: First, it was necessary to account for the fact that secondary CaCO precipitation does not fill the pore space completely, with the result that acidic brine continues to diffuse through the carbonated zone to form a CH-depleted zone. Second, secondary precipitation in brine begins via nucleation kinetics, and this could not be described with previous models using growth kinetics alone. Third, our results suggest that the CaCO precipitates in the confined pore space are more soluble than those formed in brine. This study provides a new platform for a reduced dimension model for CO attack on cement that captures the important nanoscale mechanisms influencing macroscale phenomena in subsurface environments.

Pore-Scale Modeling of Nucleation and Growth in Porous Media

“…Recently attempts have been made to incorporate CNT into the reactive transport simulators. Li et al 10 incorporated CNT in a continuum-scale reactive transport simulator to model precipitation of calcite while simulating the chemical alterations of wellbore cement in the context of wellbore integrity of CO2 storage processes. Prasianakis et al 11 coupled a pore-scale reactive transport solver with CNT to show how the homogeneous and heterogeneous precipitation kinetics can affect the evolution of a porous media.…”

The apparent activation energy and pre-exponential kinetic factor for heterogeneous calcium carbonate nucleation on quartz

“…In current numerical models that include solid phase formation, nucleation is usually approximated by precipitation on seeds of the secondary phase because the parameters required for numerically simulating nucleation process is lacking. However, the seeded model can miss important characteristics of nucleation, such as the high specific reactive surface area of nuclei and the rate-limiting role of nucleation 14,21 . To incorporate nucleation into simulations, we need a deeper understanding of its kinetic and thermodynamic parameters [21][22][23][24] .…”

Reactive Transport in Evolving Porous Media

“…The formation of secondary minerals may lead to fractures through generated internal mechanical stresses. This can lead to the deterioration of mechanical properties (Chagneau et al 2015;Li et al 2017). For cement materials, the delayed formation of ettringite (Taylor et al 2001) or atmospheric carbonation (Auroy et al 2013) are typical examples of precipitation processes that can induce fracturing, which can be detrimental in the context of CO 2 sequestration or radioactive waste management.…”

“…However, there is experimental evidence that in some cases mineral precipitation will not completely clog the porous media. Li and co-workers observed that despite the formation of a distinct calcite cement band in cement subject to CO 2 attack, the porosity did not go completely to zero as evidenced by the continued progress of the primary portlandite dissolution front (Li et al 2017). They attributed this to be due to either the lack of precipitation in nanopores that were still able to allow for diffusive transport of the uncharged H 2 CO 3 molecule into the unaltered cement, or alternatively due to continued micro-fracturing.…”

“…This is due to the fact that dissolution rates of primary minerals are affected by the diffusion of calcium through the degraded layers. Several reactive transport studies managed to adequately reproduce the extent of measured degradation depths using either Archie's law (Galíndez et al 2006;De Windt and Badreddine, 2007;Chagneau et al 2015;Li et al 2017;Georget et al 2018) or an exponential relation (Mainguy et al 2000;Seigneur et al 2017) to describe tortuosity evolution as a function of changing porosity. However, the choice of the cementation factor n or the exponential factor a differs between the studies in a way that is not straightforward to predict, depending on the conditions and the materials considered.…”