Assessment of fluid heterogeneity of the reservoirs in the J3 Formation during the construction of a two-dimensional reservoir model

Introduction. Heterogeneity of fluid saturation in the Tyumen Formation reservoirs significantly complicates the correct interpretation of well logging data and building a 2D geological model. Uncertainties associated with reservoir heterogeneity require detailed study. Current conditions necessitate the development of approaches that allow to reconstruct the reservoir structure, taking into account the complicating factors of low permeability and high discontinuity.

The objective of this study is to build a 2D geological model of the reservoir, taking into account the existing fluid heterogeneity.

Materials and methods. This study is based on well logging and core data. A capillary saturation model was built using the Brooks and Corey model. The 3D CDP seismic data was used to build the structural surfaces of the top and bottom of J3 reservoir and to interpret the shale-out zone. The reserves estimation maps were built in Isoline SW.

Results. The fluid type uncertainty analysis for the polyfacial terrigenous sediments of J3 reservoir of the Tyumen Formation are described. A comprehensive set of laboratory core studies, combined with well logging data, established a direct correlation between the degree of oil saturation in low-permeable reservoirs and their porosity and permeability properties, contrary to the general notion that it varies with reservoir height. A single well was used to demonstrate the presence of type I capillary barriers preventing complete reservoir charge within the established oil-bearing contour.

Conclusion. The geological model developed with account of reservoir fluid heterogeneity is capable of most accurate representation of the fluid type distribution patterns in reservoirs. The interpreted capillary barriers and saturation heterogeneity indicate the need for an integrated approach to the interpretation of well logging and core data. The obtained data can be used to update high-water-cut zones in developed fields with heterogeneously saturated reservoirs.

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