Injection of carbon dioxide in deep saline aquifers is considered as a method of carbon sequestration. The efficiency of this process is dependent on the fluid-fluid and rock-fluid interactions inside the porous media. For instance, the final storage capacity and total amount of capillary-trapped CO2 inside an aquifer are affected by the interfacial tension between the fluids and the contact angle between the fluids and the rock mineral surface. A thorough study of these parameters and their variations with temperature and pressure will provide a better understanding of the carbon sequestration process and thus improve predictions of the sequestration efficiency. In this study, the controversial concept of wettability alteration of quartz surfaces in the presence of supercritical carbon dioxide (sc-CO2) was investigated. A novel apparatus for measuring interfacial tension and contact angle at high temperatures and pressures based on Axisymmetric Drop Shape Analysis with no-Apex (ADSA-NA) method was developed and validated with a simple system. Densities, interfacial tensions, and dynamic contact angles of CO2/water/quartz systems were determined for a wide range of pressures and temperatures relevant to geological sequestration of CO2 in the subcritical and supercritical states. Image analysis was performed with ADSA-NA method that allows the determination of both interfacial tensions and contact angles with high accuracy. The results show that supercritical CO2 alters the wettability of quartz surface toward less water-wet conditions compared to subcritical CO2. Also we observed an increase in the water advancing contact angles with increasing temperature indicating less water-wet quartz surfaces at higher temperatures.

No abstract

The successful implementation of geologic CO 2 sequestration schemes in deep saline aquifers requires storage sites with minimum risk of CO 2 leakage through the caprock and maximum storage capacity in the reservoir rock. Some of the essential parameters that affect the effectiveness of a storage scheme are the density of CO 2 , the interfacial tension between CO 2rich and aqueous phases, and the wettability of reservoir rock and caprock in contact with these fluids at reservoir conditions [1]. In this study, densities, interfacial tensions, and dynamic contact angles of CO 2 /brine/quartz systems at high temperatures and pressures were simultaneously measured using the Axisymmetric Drop Shape Analysis with no-Apex (ADSA-NA) method. Measurements were performed at pressures (2000-4000 psig), temperatures (50-100 °C), and brine salinities (0.2 to 5 M) relevant to carbon sequestration in deep saline aquifers. These experimental conditions had not been investigated in the past. Additionally, the effect of SO 2 as a co-contaminant (0-6 wt.%) was investigated on these parameters for the first time. Contact angle hysteresis was also examined and the possible implications of the results on different CO 2 trapping mechanisms were discussed.

A model of the dominant molecular and stable colloidal structures of asphaltenes has been proposed, the Yen− Mullins model. The formation of clusters of asphaltene nanoaggregates in toluene was reported elsewhere to occur at a concentration of a few grams per liter with a cluster aggregation number of approximately 8 (Mullins, O. C. Energy Fuels 2010, 24, 2179−2207). Here, we measure the DC-conductivity signal of toluene as a function of asphaltene concentration obtaining support for the critical clustering concentration (CCC) of a roughly 1.7 g/L in toluene. In addition, the small change in the Stokes drag at the CCC indicates that the cluster aggregation number is small, less than 10. The temperature variation of the CCC is measured to be small and within error, suggesting that cluster formation is entropically driven. Centrifugation experiments were also performed on asphaltene−toluene solutions at different concentrations. These experiments confirmed that a significant change in asphaltene aggregation occurs in the concentration range of the CCC. The CCC values from centrifugation and DC-conductivity measurements are roughly the same. The centrifugation experiments confirm a cluster size of ∼5 nm corroborating the small aggregation number found in the DC-conductivity experiments. These results add to the growing body of literature validating the Yen−Mullins model.

No abstract