Influence of temperature and pressure on quartz–water–CO 2 contact angle and CO 2 –water interfacial tension Mohammad Sarmadivaleh, Ahmed Z. Al-Yaseri, Stefan Iglauer ⇑ Curtin University, Department of Petroleum Engineering, 26 Dick Perry Avenue, 6151 Kensington, Australia article info Article history: Received 10 September 2014 Accepted 2 November 2014 Available online 20 November 2014 Keywords: Carbon geo-sequestration Residual trapping Structural trapping Interfacial tension Contact angle Quartz Carbon dioxide Temperature abstract We measured water–CO 2 contact angles on a smooth quartz surface (RMS surface roughness 40 nm) as a function of pressure and temperature. The advancing water contact angle h was 0° at 0.1 MPa CO 2 pressure and all temperatures tested (296–343 K); h increased significantly with increasing pressure and temperature (h = 35° at 296 K and h = 56° at 343 K at 20 MPa). A larger h implies less structural and residual trapping and thus lower CO 2 storage capacities at higher pressures and temperatures. Furthermore we did not identify any significant influence of CO 2 –water equilibration on h. Moreover, we measured the CO 2 –water interfacial tension c and found that c strongly decreased with increasing pressure up to 10 MPa, and then decreased with a smaller slope with further increasing pressure. c also increased with increasing temperature. Ó 2014 Elsevier Inc. All rights reserved. 1. Introduction Carbon geo-storage (CGS) has been recognized as a key technol- ogy to substantially reduce anthropogenic CO 2 emissions to the atmosphere and thus mitigate climate change [1]. In CGS, CO 2 is pressed into subsurface formations for storage, i.e. into deep saline aquifers or oil and gas reservoirs for enhanced hydrocarbon production [1–4]. However, CO 2 is buoyant because it has a lower density than the formation brine and consequently flows upwards. Four trapping mechanisms prevent the CO 2 from leaking to the surface: (1) Structural trapping [5], (2) Residual trapping [6,7], (3) Dissolution trapping [8] and (4) Mineral trapping [9]. In this context, the wettability of a rock–CO 2 –water system plays a crucial role as it strongly impacts on the two most important trapping mechanisms, namely structural [10–12] and residual trapping [7,13,14], and thus also indirectly on dissolution and mineral trapping [12,15]. It is therefore necessary to understand the interfacial character- istics of the rock-fluid–fluid system in more depth to reduce project risk. Specifically the contact angle between the rock, water and gas h – which quantifies wettability of a mineral substrate [13,17] – and the gas–water interfacial tension c strongly affect residual satura- tions [14,18–20], and the column height of CO 2 (i.e. volume) which can be permanently immobilized beneath a caprock [11,12]. Wettability also significantly influences relative permeabilities [21–23] and capillary pressures [8,13,24–26] and thus reservoir scale (hectometre scale) flow predictions. In fact relative perme- abilities and capillary pressures are essential input parameters into reservoir simulators and the output computations are very sensi- tive to these parameters [27]; so it is important to precisely know these quantities. In order to study the rock–CO 2 –water wettability, several researchers measured water–CO 2 contact angles on silica sub- strates (as a representative of sandstone) and CO 2 –water interfacial tensions at low to high pressure conditions [28–50]. It is clear that c drops with increasing pressure, and there is evidence that c increases with increasing temperature [32,36,45,46]; furthermore, it appears that h increases with increasing pressure although the uncertainty associated with the h measurements is high, cp. the recent review published by Iglauer et al. [13]. This is also true for the influence of temperature on h, no clear trend could be identified and less data is available, particularly there is a lack of systematic investigations. In this context, Saraji et al. [45] and Farokhpoor et al. [47] mea- sured an increase in h with increasing pressure and temperature for deionized (DI) water ([45]: from 12° at approximately 4 MPa and 308 K to 35° at 333 K at 8–12 MPa; [47]: from 10° at 309 K to 20° at 339 K over a pressure range of 35 MPa; Fig. 3). In contrast, Saraji et al. [46] reported a slight decrease in h (by up to 5°) with increasing temperature (333–353 K) at high http://dx.doi.org/10.1016/j.jcis.2014.11.010 0021-9797/Ó 2014 Elsevier Inc. All rights reserved. ⇑ Corresponding author. Fax: +61 8 9266 7063. E-mail address: stefan.iglauer@curtin.edu.au (S. Iglauer). Journal of Colloid and Interface Science 441 (2015) 59–64 Contents lists available at ScienceDirect Journal of Colloid and Interface Science www.elsevier.com/locate/jcis