According to the literature and our own experimental data, the known types of residual oils, methods for determining the predominant type of residual oils for the oil reservoir targeted stimulation in order to increase oil recovery are considered. The qualitative characteristics of the properties of residual oils, by which it is possible to assess their changes by modern technical means are revealed. At residual oils additional displacement from the water-flooded reservoir, the phase state of the reservoir fluids, due to the redistribution of components between two reservoir fluids (reservoir water and residual oil), as well as a change in the phase state depending on the saturation of the oil - solid phase and wax precipitation in reservoir conditions - play an important role. Examples of studying at a particular field not only the composition of the residual oil, but also the degree of development of reservoir reserves under conditions of its washing with fresh water, when oil wells geophysical prospecting can't provide reliable information about the oil saturation of different intervals of the reservoir in the flooded area, are given. The change in the phase state (wax precipitation in reservoir conditions) of surface samples and degassed deep oil samples taken from the same oil well in different years are given. It is recommended for the analysis of changes in the properties of reservoir fluids to create an operational data bank with a data monitoring function, the ability to build maps and histograms of the distribution of physical and chemical properties both along the strike and along the depth of the beds.
The obtained on the basis of areal and temporary monitoring information on changes in the properties of reservoir fluids allows to identify the oil reservoir zones with varying degrees of oil saturation and assess the quality of residual oils, which makes it possible to monitor the state of the developed deposit and adopt optimal management decisions.
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