The article reveals methodological issues of laboratory flow tests to measure the oil-water displacement ratio. Example data for thin-layered heterogeneous reservoirs presents some cases when researchers go beyond the “classical” industry standards, and this leads to distortions in the assessment of the displacement ratio coefficient. The first violation is non-compliance of the core sample length similarity criterion (Efros criterion). Flow tests are often carried out with single core samples (separate plugs) due to the high reservoir heterogeneity and the limited amount of core material. A positive effect of this approach is the detailing of the reservoir structure, which can later be taken into account in hydrodynamic modeling. However, in the pursuit of additional information, researchers skip the basic step of sample selection – calculation of the minimum length of the core column for the flow test. The area of border effects becomes comparable to the size of the entire core sample when using single samples, and this leads to an incorrect assessment of its saturation. Formal calculations indicate the need to use composite core columns rather than single samples when working with highly permeable intervals. The second significant violation is non-compliance with the content of residual water (or initial oil saturation) in the core sample and in the real reservoir. The authors give an example where researchers displace too much water during the formation of residual water saturation. Mismatch between the initial oil saturation values in the laboratory flow tests and in the reservoir description documents can lead to a significant overestimation of the displacement coefficient and, in general, to overestimation of recoverable reserves values.
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