Molecular Dynamics Simulation of Water/CO2-quartz Interfacial Properties: Application to Subsurface Gas Injection

Abstract

Global warming due to Carbon Dioxide (CO 2 ) emissions from fossil fuel consumption remains an extremely difficult problem to mitigate. One of the many purposed methods to tackle rising emissions of CO 2 is subsurface injection into geological formations known as Carbon Capture and Storage (CCS).A major challenge, that projects involving subsurface gas injection have, is predicting the amount of gas that will be trapped in the formation effectively and safely. A major contributing factor to this uncertainty is the lack of accurate experimental data on contact angles between the subsurface rocks, formation water and CO 2 . The two main difficulties with employing experimental work to estimate these parameters are the existence of partially contradicting results and the difficulty in accurately recreating the range of subsurface conditions in the laboratory. Molecular dynamics computer simulations provide a microscopic approach to recreate subsurface conditions and to explain experimental contradicting results.We report here molecular dynamics investigations on the influence of divalent salts on the CO 2 /water/quartz contact angle. We also investigate N 2 /water/quartz and H 2 S/water/quartz systems, in order to assess the impact that the gas has on the contact angles. The quartz surface used for these simulations was a fully coordinated quartz crystal. In addition, we present results for a hydroxylated quartz crystal model, which we have developed for this work. The dependence of the contact angles on the degree of hydroxylation is discussed.

Receding and advancing (CO 2 + brine + quartz) contact angles as a function of pressure, temperature, surface roughness, salt type and salinity

“…However, h a and h r both increased with pressure, up to h a = 34°and h r = 13°at and T = 296 K (figures 4 and 5). The increase in h a and h r with increasing pressure was also observed for experiments conducted at T = (323 and 343) K (figures 4 and 5), which is consistent with most of the literature data [10,12,15,[25][26][27][28][29][30][31], and molecular dynamics (MD) simulations [32][33][34]. Iglauer et al [33] explained this behaviour by rapid increase in CO 2 density with pressure, which strengthens the intermolecular interactions between CO 2 and quartz, and thus leads to de-wetting of the surface.…”

“…Furthermore, the molecular dynamics (MD) simulations found that contact angles decrease with increasing temperature [33]; the discrepancy between the MD predictions and the measurements are probably due to the inadequate representation of the quartz surface chemistry (which is complex [36]) in the MD model, e.g. surface silanol groups exist [37] and significantly lower h [34]; furthermore the silanol groups can dissociate, and this has not been implemented into the MD models yet.…”

Influence of CO2‐wettability on CO2 migration and trapping capacity in deep saline aquifers

“…[3][4][5][6][7][8] Among all these types of CO 2 storage sites, deep saline aquifers are considered more suitable, because they have the largest CO 2 storage capacity and the widest geographical spread. 13,27,[29][30][31][32][33][34][35][36][37][38][39] Wettability, as has been previously shown in laboratory experiments (at the mm to cm scale), has a significant effect on residual trapping 15,[40][41][42] and structural trapping. Indeed, water contact angles between 0°(strongly water-wet) and 170°(strongly CO 2 -wet) have been measured, where CO 2 -wettability mainly depends on the surface chemistry, and to a lesser extent on temperature, pressure, and brine composition.…”

“…31,32,35,36,53 Thus, to perform hectometer-scale reservoir simulations, an upscaling mechanism is required. 31,32,35,36,53 Thus, to perform hectometer-scale reservoir simulations, an upscaling mechanism is required.…”

Impact of fines and rock wettability on reservoir formation damage

“…As discussed earlier (Al‐Yaseri et al . ), silanol groups on the water‐wet quartz surface (Zhuravlev ; McCaughan, Iglauer, and Bresme ) strongly attract the hydroxyl groups on the water‐wet Barite surface (Fenter et al . ).…”