Experimental and Theoretical Study of Microstructural Wettability of Oil and Gas Reservoirs

Abstract

AbstractWettability of the rock surface is an important parameter. Wettability of the rock surface is a key parameter which determines the development efficiency of any field. Effective solution of such problems as evaluation tasks of reservoir properties, simulation of two-phase filtration processes, determination of oil recovery factor, substantiation of formation and bottom oil area stimulation methods is associated with the adequacy of the existing concepts of wettability determination and the real wettability of the formation. However, the established ideas about wettability, laid down in standards and techniques, were based on research conducted in the last quarter of the XX century and currently need to be updated, as it was based on homogeneous type of wetting. Thus, substantiating of the new perception about wettability and determination methods is an actual task for effective enhancement of oil and gas fields development. In this paper the results of theoretical and experimental studies of the effect of the pore space microstructure on the hydrophobization of oil and gas reservoirs are presented. A new type of heterogeneous wettability – microstructural wettability, and a possible mechanism of formation is described here. The mechanism of the microstructural wettability formation demonstrates that hydrophobization of the inner pore space in mixed wettability can be associated either with large or small pore sizes. It was proven experimentally that the process of hydrocarbon adsorption depends on the shape, size, and distribution of pores, the mineralogical composition (particle composition and size, presence of clay), as well as on the time of contact of hydrocarbons with the inner pore surface. The concept of the hydrophilic nature of rock prior to the migration of oil into it can be considered as accurate. However, as was shown in the experiments, oil can present in the small pores (up to 10 μm), which is especially significant for the carbonate reservoirs.