On the Wetting of Carbonate Surfaces By Oil And Water

Abstract

Abstract The relaxation of initially advancing and receding contact angles has been studied for two basic systems, water/ saturated air/marble, and aqueous solution/oil/marble, and static advancing contact angles have been studied in the water/air/marble system. All experiments were conducted at room temperature but other experimental conditions have been varied so as to permit comparison between these laboratory results and certain aspects of the recovery of oil from limestone fields. A preliminary study also has been made to elucidate which components of crude oil affect the wettability of calcium carbonate, and to assess the stability of the adsorbed layers to solvent attack and to oxidation. AN IMPORTANT FACTOR influencing the efficiency of secondary recovery of oil from limestone strata by waterflood is the ability of water to displace oil from capillaries within the rock. It is well established that changing the wettability of the porous medium from oil-wet to water-wet during the displacement by water enhances oil recovery. In such processes both the dynamic and static oil/water/rock contact angles play fundamental roles. This work is intended to improve our understanding of the fundamental properties of the types of interfaces which determine these contact angles. In particular, dynamic aspects of the wetting of a carbonate surface are considered. This paper presents the results of experiments designed to simulate certain aspects of the recovery of oil from such strata and to determine the nature of the surface-active substances in the oil. This latter study involves investigation of the influences on the wettability of marble, and of the stability to oxidation and to solvent attack, of layers of these substances adsorbed at the marble surface. Marble was chosen asthe experimental surface because it can be regarded as the idealized surface of a limestone reservoir and because of its suitability for use with techniques well established in these laboratories(1–6). The smooth marble surfaces, which are chemically similar to the reservoir surfaces, give a well-defined geometrically simple model system in which reproducible contact angles can be measured. However, the size and distribution of micropores in the surface layers differ from that found in natural oil-bearing strata because the surfaces were either polished or finely ground. Apparatus and experimental techniques Material Distilled water was re-distilled from alkaline permanganate under an atmosphere of nitrogen in an all glass, grease-free apparatus. The hydrocarbon oil, Bayol D (kindly supplied by the Iraq Petroleum Co. Ltd.), exhibited a surface tension (Sugden's maximum bubble pressure method) and an interfacial tension (Wilhelmy plate method) against water of 28.5 ±O.3 and 49.5 ±0.5 dyne cm−1 respectively after passage through an activated alumina column, which treatment removed a yellow band from the oil. Bayol D is a light-fraction paraffin mixture said to contain no branched molecules. Oil saturated with water was produced by storage over water, with periodic stirring, for 5 days, and exhibited a limiting interfacial tension against water 45.0 ±0.5 dyne cm−1.