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

Abstract

Wettability 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.

Determination of Sessile Drop Wetting Angle Based on μCT without the Direct Angle Measurement

“…There are direct and indirect methods for determining wettability. Direct quantitative methods include measurement of the contact angle (θ) and the isothermal drying method . Indirect methods comprise Amott, USBM, liquid adsorption, capillary pressure curves, capillary impregnation, relative phase permeability curves, nuclear magnetic resonance, etc.…”

“…Direct quantitative methods include measurement of the contact angle (θ) and the isothermal drying method. 8 Indirect methods comprise Amott, 9 USBM, 10 liquid adsorption, 11 capillary pressure curves, 7 capillary impregnation, 12 relative phase permeability curves, 13 nuclear magnetic resonance, 14 Most approaches for wettability determination give an integral characteristic of wetting, which does not take into account the structure of the pore space. At the same time, it is important to preserve the natural state of the surface of the rock sample for laboratory wettability studies.…”

Adsorbed residual oil saturation and phase permeability relationship for oil in Western Siberia productive formations

“…Особую значимость эта процедура приобретает в связи с интенсивным вводом в разработку залежей с трудноизвлекаемыми запасами, характери-зующихся низкой проницаемостью [16][17][18]. Причем доля этих залежей как в карбонатных, так и в терригенных коллекторах с каждым годом увеличивается [19][20][21]. Растет и доля вводимых в разработку месторождений, не имеющих аналогов среди залежей, находящихся длительное время в разработке [22][23][24].…”