New representations of wettability of oil and gas reservoirs
Key words: microstructure, reservoir, hydrocarbons, wettability, capillary pressure, disjoining pressure
Authors: N.N. Mikhailov (Gubkin Russian State University of Oil and Gas, RF, Moscow), I.P. Gurbatova (PermNIPIneft Branch of LUKOIL-Engineering LLC in Perm, RF, Perm), K.A. Motorova (Lomonosov Moscow State University, RF, Moscow), L.S. Sechina (Oil and Gas Research Institute of RAS, RF, Moscow)
This paper discusses a wide range of physical and geological factors that determine the wettability of oil and gas reservoirs. Wettability is an important parameter in oil recovery as it affects relative permeability characteristics, capillary pressure, electrical properties and other characteristics of the reservoir. Neglecting the effects of wetting causes erroneous distribution of saturation in geological modeling and development of substandard forward-looking indicators in simulation. Existing types of wettability and their applications were analyzed: strongly water-wet, strongly oil-wet, neutrally wet and fractional wettability. The phenomenon of hydrophobic pore surface by adsorption of surfactants (polar) oil components in the natural hydrophilic mineral surfaces was considered. On the basis of modern ideas about the physics of microscopic processes in porous media and stages of the geological formation of deposits substantiates a type of fractional wettability –microstructural wettability in which the oil-wet and water-wet surfaces of pores and capillaries have various wettability. Hydrophobization at pores and channels forms microstructural wettability, since pores of different size, shape and mineral composition different hydrophobized and therefore have different wettability. In the process of water repellency decreases the amount of free long oil takes a different size pores and in various forms (film, meniscus, contact), change the configuration of the pore space (in the presence of hydrocarbons configuration smoothed). These phenomena lead to the need for a detailed study of the physics of water-repellency at the micro level. There is connection between pore space structure and pores form of the rock and wettability of all pores size range. Along with the identified patterns of adsorption of hydrocarbons, depending on the shape, size and distribution of pores, they also investigated the effect of mineralogical composition (composition and particle size, the presence of clay) pore surface adsorption of water and oil phases. The conclusions from these studies are that the composition of the rock also significantly affects the adsorption processes.
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