Justification of the heights of the sediments of the Tyumen suite using indirect methods

The studied sediments of the Tyumen suite can be characterized by difficulties in confirming oil saturation coefficients derived from well testing data, including the electrical resistivity. Alternative estimation of oil saturation using a capillary model is complicated. This is because the above-mentioned sediments have a complex deposit structure. In some instances, these deposits are limited by a conventionally accepted depth of the lower oil-saturated interval, without justifying the free water level. For this reason, we must estimate deposit heights indirectly using only core analysis data. This article aims to develop indirect methods for evaluating deposit height within the constraints of geological models. To achieve this aim, we first generalized and analyzed capillary properties under both atmospheric and thermobaric conditions. We utilized direct indicators of oil saturation from core fluorescence under ultraviolet light, to determine boundary values for reservoir properties in the zone of maximum saturation. We then selected appropriate values for residual water saturation. Using these values, we compared total porosity with effective and dynamic porosity and obtained consistent boundary values. Based on the established values for residual water saturation and available capillary pressure curves, we calculated capillary pressures and formation heights. As a result, the results show that capillary pressures ranging from 7 atm to 12 atm are sufficient to establish residual water saturation in the Tyumen suite deposits within the studied areas. These pressures correlate to reservoir heights between 90 to 160 m. This approach facilitates the estimation of oil saturation coefficients using the capillary model in reservoirs with uncertain fluid contacts. It can also serve as supplementary tool for justifying individual lenses and blocks within geological models.

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