Wettability Phenomena at the CO₂–Brine–Mineral Interface: Implications for Geologic Carbon Sequestration

Abstract

Geologic carbon sequestration (GCS) in deep saline aquifers results in chemical and transport processes that are impacted by the wettability characteristics of formation solid phases in contact with connate brines and injected CO(2). Here, the contact angle (θ) at the CO(2)-brine-mineral interface is studied for several representative solids including quartz, microcline, calcite, kaolinite, phlogopite, and illite under a range of GCS conditions. All were found to be water wetting (θ < 30°) with subtle but important differences in contact angles observed between the surfaces. Temperature and pressure conditions affected the results but did not produce discernible trends common to all surfaces. Brine composition, in terms of pH and ionic strength, was a better predictor of interfacial behavior. For the nonclays, the wettability is impacted by the pH at the point of zero charge of the solid. For the clays, the response was more complex. Under nonequilibrium conditions, hysteretic effects were observed when CO(2) was dissolving into the bulk fluid and this effect varied between minerals. Contact angle was found to decrease during the CO(2) phase transition from supercritical or liquid phase to gas phase. These results are useful for developing a more complete understanding of leakage through caprocks and capillary trapping in GCS.

Direct Measurement of Static and Dynamic Contact Angles Using a Random Micromodel Considering Geological CO2 Sequestration

“…Average contact angles on flat surface inside micromodel at pressure of one and eight megapascals are 62° ± 7° and 49° ± 21°, respectively, in agreement with Kim et al [58] observations showing a wide range of contact angles from 40° to 80° inside a uniform micromodel. Contact angles on a flat surface in this study are higher than those shown in previous sessile drop or captive bubble tests with large droplet of water or bubble of CO2 (i.e., 8° to 45° on silica or glass surface) [18,22,43,[50][51][52]. This could be due to the micro-scaled CO2 bubble size on a flat surface inside the micromodel of [18,22,43,[50][51][52].…”

“…Contact angles on a flat surface in this study are higher than those shown in previous sessile drop or captive bubble tests with large droplet of water or bubble of CO2 (i.e., 8° to 45° on silica or glass surface) [18,22,43,[50][51][52]. This could be due to the micro-scaled CO2 bubble size on a flat surface inside the micromodel of [18,22,43,[50][51][52]. This could be due to the micro-scaled CO 2 bubble size on a flat surface inside the micromodel of the present study in comparison with the other studies with larger dimension of bubble ranging from a few to tens of millimeter.…”

“…Because of different level of relaxation of the interfaces, various mode of interfaces before stoppage (i.e., receding or advancing), and pinning effect originated from solid surface imperfection, SCA shows wide range of values for the two different tests and also for each test in any throat sizes. The range of SCA at each pore throat size is higher than that of equilibrium contact angle (ECA) measured with CO 2 or water droplet on flat surface (i.e., 8 • to 45 • on silica or glass surface) [18,22,43,[50][51][52]. Static contact angle during drainage and imbibition processes.…”

Fundamental study of CO2-H2O-mineral interactions for carbon sequestration, with emphasis on the nature of the supercritical fluid-mineral interface.

“…Previous work in the CO 2 storage literature related to the changing magnitude of the chemical potential of water and/or adsorptive and capillary water focuses mainly on: 1) near-wellbore saline water evaporation and concomitant salt precipitation that may reduce scCO 2 injection rates due to permeability losses [16,17,[28][29][30]; 2) chemical reactivity under humid scCO 2 including precipation-dissolution and water intercalation in clays as a function of water content in scCO 2 [7,10,[31][32][33][34][35][36]; and 3) laboratory observation or theoretical estimation of thickness of water films in scCO 2 [26,27,37]. Common approaches for assessing near-wellbore dry-out, in calculating water activity in the CO 2 -rich phase, typically neglect any effects of capillary potential or surface adsorption potential on the total chemical potential of water [e.g., see 36,38].…”

“…Moreover, alteration that changes surface mineralogy or morphology can lead to altered wettability. Mineral wetting properties strongly affect reservoir permeability with respect to water and the supercritical phase, play a key role in determining integrity of caprock seals, and control capillary and residual trapping processes and hence, reservoir storage capacity estimates [79].…”