Basic ideas about the curves of capillary displacement and their characteristics (review)

UDK: 622.276.031:
DOI: 10.24887/0028-2448-2018-8-24-28
Key words: capillary number, pinched saturation, mobilization threshold, displacement threshold, residual oil, capillary displacement curves, formation regimes of residual oil
Authors: N.N. Mikhailov (Gubkin Russian State University of Oil and Gas (National Research University), RF, Moscow; Oil and Gas Research Institute of RAS, RF, Moscow), S.V. Melekhin (PermNIPIneft Branch of LUKOIL-Engeneering LLC in Perm, RF, Perm)

The results of an experimental study of the curves of capillary displacement of wetting and non-wetting phases of fluids are analyzed. The theory of the capillary number is analyzed and the conditions for the adequacy of this parameter for various types of reservoir and fluids are shown. For the first time a systematic review of foreign and Russian studies for a sixty-year period of studying the curves of capillary displacement is presented. Classical and non-classical experiments of obtaining these curves in a wide range of changes in the number of capillarity are analyzed. The general regularities and features of the behavior of these curves under various experimental conditions, as well as in the absence of the unified methodology for their production, are revealed. It was demonstrated that, unlike the experiments carried out on the Berea and Fontainebleau model cores, the capillary displacement curves change when the structure of the pore space of wettability, porosity, permeability and other reservoir properties of the formation changes. Unlike foreign ones, in Russian publications this problem is reflected in a fragmented way. The generalization of the results allowed the authors to establish a wide range of changes in the threshold for the mobilization of residual oil for rocks with different reservoir properties. Previously conducted foreign and Russian experiments demonstrated the significance of the mobilization threshold in a narrow range of variation in the capillarity numbers. In this paper, based on the structure of the residual oil saturation, the existence of a new parameter - the threshold for the displacement of the capillary-clamped saturation and the corresponding value of capillarity numbers - is justified. The values of the displacement threshold are controlled by the relationship between the tightly bound and the conditionally mobile saturation. The magnitude of the displacement threshold depends on the reservoir properties and wettability. Accounting for the structure of residual oil leads to a nonclassical appearance of the curves of capillary displacement. Various forms of representing the curves of capillary displacement for different types of oil and gas collectors and for various types of saturation are demonstrated.A comparison of the classical and nonclassical curves of capillary displacement indicates a significant variability of these curves for rocks with a different pore space structure and wettability. Despite the proven effectiveness of the capillary displacement curves, the systematic study and accounting of these curves in determining the basic filtration properties and designing the development of the deposit in Russia is not currently carried out.


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