Surface energy characterization of sandstone rocks Naveed Arsalan a , Sujeewa S. Palayangoda a , Daniel J. Burnett b , Johannes J. Buiting c , Quoc P. Nguyen a,n a Department of Petroleum and Geosystems Engineering, The University of Texas at Austin,1 University Station, C0300, Austin, TX 78712-1061, USA b Surface Measurement Systems, 2125 28th Street SW, Suite 1, Allentown, PA 18103, USA c Saudi Aramco, P.O. Box 11391, Dhahran 31311, Saudi Arabia article info Article history: Received 3 December 2012 Received in revised form 22 February 2013 Accepted 26 February 2013 Available online 16 March 2013 Keywords: A. Interfaces A. Multilayers C. Photoelectron spectroscopy C. X-ray diffraction D. Surface properties abstract The fundamental forces of adhesion are responsible for the spreading of fluids such as crude oil/brine on the reservoir rock surface. These physico–chemical interactions determine the surface energetics of a reservoir and thus their wetting phenomena. Inverse Gas Chromatography (IGC) is introduced to characterize the surface energy of sandstones (Ottawa sand and Berea sandstone). The surface chemistry of the sandstone rocks is further elucidated using X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) techniques. The behavior of the polar and non-polar interaction forces was investigated at varying water coverage and at different temperatures. The results indicated that in general as the water coverage increased, the Lifshitz–van der Waals component of surface energy decreased to nearly that of the bulk water, while the acid–base component also showed a decreasing trend. The Lifshitz–van der Waals component of surface energy always decreased with increase in temperature, while the acid–base properties showed contrasting trends in line with changes in surface chemistry of the sandstones, due to the change in temperature. Finally, the wetting properties arising in reservoir sandstones were related to the surface chemistry of the reservoir fluids and their interactions with the reservoir rock surface. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction An accurate description of the surface chemistry of a reservoir rock is essential to understand the attractive forces between the crudes, brines and the rock surface. These physico–chemical inter- actions determine the fundamental nature of the reservoir proper- ties such as rock wettability. Wettability describes the tendency of a fluid to spread on a rock surface in the presence of another immiscible fluid. Based on the affinity of the rock surface towards oil and water phase, the reservoir is termed oil wet, water wet or intermediate wet. Wetting characteristics of a rock surface control important parameters such as capillary pressure and relative permeability and hence influence reservoir production, waterflood recovery and the performance of Enhanced Oil Recovery (EOR) processes. The conditions that establish a given reservoir wettability are not well known. Reservoir rock is a high-energy surface with well developed pores and large surface/volume ratio. It can strongly adsorb polar molecules such as surfactants and polymers resulting in the change of wettability. The wettability of the rock could also be changed due to the interactions with surface active agents present in both the aqueous and oil phase. Thus, an attempt is made to understand the interactions between the reservoir fluids and the rock surface which are responsible for the adhesion phenomena. These interactions are physical and chemical in nature, which determine the energy of forming a unit area of interface. As a result, the characterization of surface energetics is essential for an improved understanding of the factors affecting the reservoir wettability to accurately predict the reservoir performance. Sandstone and carbonate reservoirs are dominant petroleum producers. Thus, the objective of this paper is to investigate the surface energetics of sandstone rocks subjected to varying water coverage at different temperatures and understand the forces that play a crucial role at the rock–water interface before the oil migration. In particular, this investigation will focus on two sandstone rocks – Ottawa sand and Berea sandstone. Ottawa sand comprises of rounded grains of clear and colorless quartz (SiO 2 ), uncontaminated by clay. However Berea sandstone is a fairly homogeneous rock containing some clay. Due to its industrial importance, silica has been an extensively studied surface. However, one observes a wide variance in the test silica surfaces [1–3], the methods used to study them [4–6] and thus the surface energy pattern displayed in literature. As a result, it remains an active object of study [7]. In the absence of a defined surface characterization of sandstone rocks, attempts have been made to correlate the wettability of a mineral with the composi- tion of crude oil [8,9] by isolating the acidic and basic components of the crude oil. However, the surface chemistry of the rock surface Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jpcs Journal of Physics and Chemistry of Solids 0022-3697/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jpcs.2013.02.027 n Corresponding author. Tel.: þ1 5124711204; fax: þ1 5124719605. E-mail address: quoc_p_nguyen@mail.utexas.edu (Q.P. Nguyen). Journal of Physics and Chemistry of Solids 74 (2013) 1069–1077