Contents lists available at ScienceDirect Journal of Petroleum Science and Engineering journal homepage: www.elsevier.com/locate/petrol The study of influence of electromagnetic waves on the wettability alteration of oil-wet calcite: Imprints in surface properties Jaber Taheri-Shakib a , Ali Shekarifard a,* , Hassan Naderi b a Institute of Petroleum Engineering, School of Chemical Engineering, College of Engineering, University of Tehran, Tehran, Iran b Research Institute of Petroleum Industry, Department of Research and Technology of the Rock and Fluid Reservoirs, Tehran, Iran ARTICLE INFO Keywords: Wettability Heavy oil Microwave Calcite Polar ABSTRACT The wettability of reservoir rock is one of the fundamental parameters determining the flow of fluid in the porous media. This study has investigated the effect of microwaves on the wettability of calcite reservoir rock from Yaran, Iran, as the time interval of microwave radiation is one of the most important parameters affecting wettability. The reservoir rock samples were placed in a microwave oven filled with helium gas and subjected to microwave radiation at 5-min intervals from 5 to 35 min. Measurements of the contact angle between the oil and the rock indicated that the microwaves brought the angle from about 120° primary state to 93° at 35 min. At intervals of 5–15 min, no change in the wettability of the oil-wet rock was observed. Sulfur components had high absorption coefficients of microwaves, so initially reduced the amount of sulfur (S) on the surface of the oil-wet rock. Next, the nitrogen (N) and oxygen (O) elements were reduced, and eventually the carbon (C) levels began to decrease. This trend was observed in the zeta potential by changing the surface charge of the rock. Indeed, eliminating SNO polar compounds with a high potential for absorbing microwave caused the rock to become water-wet. Microwave radiation initially produced no change in the Fourier-transform infrared spectroscopy (FTIR) spectrum, as it continued, the peak intensity of the corresponding oil, such as the carboxylic acid functional group, declined, and the corresponding peaks of the rock became more intense, indicating a gradual change in the wettability. It can be interpreted that the aromatic compounds exist in oil and act as surface agent components. The results of this study can be used as a representation of the use of microwave radiation in hydrocarbon reservoirs to change the wettability and increase the production rate of reservoirs. 1. Introduction Wettability plays an important role in the production of oil in hy- drocarbon reservoirs: it not only determines the initial distribution of fluids, but is also an important factor in the process of fluid flow in the porous medium of the reservoir. In hydrocarbon reservoirs, wettability is known to be an important factor in controlling the location, flow and distribution of fluids in the reservoir. Wetting has a great influence on the flow of fluid during oil production from the reservoir (Ahmed, 2006). It also has a great influence on relative permeability, capillary pressure, flooding efficiency, recovery factor, residual oil saturation, irreducible water saturation, electrical properties of reservoir rock and in-situ oil calculations. Reservoir wettability depends on several factors (Ahmed and McKinney, 2011): 1) Type and material of the reservoir rock. 2) Geometry of pore spaces. 3) Temperature and pressure. 4) Oil properties and composition, especially asphaltene content. 5) Proper- ties and composition of formation water, salinity and pH. Wettability is one of the main factors in controlling multiphase fluid flow, which has a significant effect on oil production from reservoirs (Nr, 1995). Compared to water-wet reservoirs (light oil reservoirs), most of the world's reservoirs are oil-wet (heavy oil reservoirs) (Anderson, 1986a; Zhou et al., 2000; Rao et al., 1992). Initial research has shown that altering the wettability toward water-wet will increase the oil recovery (Wagner and Leach, 1959). In primary and secondary oil recovery from reservoirs, wettability and natural fractures patterns play a key role in fluid flow in porous media (Shakib et al., 2015; Taheri-Shakib et al., 2018a). If the reservoir wettability is shifted from a strongly oil-wet to a neutral wet state, the capillary forces that caused remaining of oil in the porous medium reduced and then removed (Salathiel, 1973). The change in wettability towards more water-wet can substantially improve the efficiency of the oil displacement in the porous medium, thus increasing the production from the reservoir. Hence, many studies have been conducted on changes to oil wettability to increase production. Al-Anssari et al. used silica nanofluid to change the wettability of https://doi.org/10.1016/j.petrol.2018.04.062 Received 15 September 2017; Received in revised form 27 April 2018; Accepted 29 April 2018 * Corresponding author. E-mail address: ashekary@ut.ac.ir (A. Shekarifard). Journal of Petroleum Science and Engineering 168 (2018) 1–7 Available online 04 May 2018 0920-4105/ © 2018 Published by Elsevier B.V. T