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The paper presents the void space configuration and geometry models for the Lower Devonian and Upper Silurian reservoirs of R.Trebs oil field. The productive formations are characterized by heterogeneity and complex architecture of the pore space which includes practically all types of voids – primary and secondary or epigenetic pores, fractures and solution vugs developed along fractures. The study reviews small to large scale methods for analysis of vug component as a fraction of the void volume in the reservoirs – laboratory (thin sections, conventional core plugs and whole or full-diameter core samples), rock physics (sonic waveform logging, nuclear magnetic resonance, imagers) and production logs (flow profile, productivity). The results are used to develop simplified models for reservoir characterization of the pore space architecture for the Lower Devonian and Upper Silurian productive formations and also to identify trends in well productivity as a function or rock physics properties of the reservoirs.

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SUMMARYThe paper reviews the problems of differentiation of reservoirs with mixed types of voids including fractures, vugs and moldic pores for heterogeneous Lower Devonian and Upper Silurian carbonates of R. Trebsa oilfield (NAO) and Tournaisian-Frasnian carbonates of Tabynskoe oilfield (Bashkortostan) using core, wireline logs and production tests. The algorithms are presented to obtain additional information on textural features of the reservoir facies from integration of core data with results of extended logging suite. The study results in the reservoir flow model based on the ratio of connected pores, secondary voids, clay content by volume and to a greater extent relative shaliness. Matching of permeabilities measured on samples in the laboratory both on wholesized core and plugs to permeabilities estimated from well logs and flow tests revealed their different combinations in high-productivity and low-productivity wells producing from complex carbonates ranging in age from Upper Silurian to Lower Devonian on R. Trebsa oilfield and Upper Devonian to Lower Carboniferous on Tabynskoe oilfield. The integrated reservoir characterization from core data, special and standard methods of well logging, flow tests and production tests results in a new classification of reservoir facies and estimation of the range of the poroperm properties for the identified classes.

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