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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.

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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SUMMARYThe objective of the research is a reference framework set of petrophysical data characterizing the Devonian siliciclastic sediments of the study area. The characterization workflow includes three main stages: the first is the lithological typification from core description, the second is matching of the identified lithotypes with their petrophysical properties and the third is testing the model against wireline logging data. The core from selected wells was described for lithological typification and studied with routine and special core analysis procedures in the laboratory. It is well known that shale content changes the physical properties of the rock, hence the results of the particle size distribution analysis were used to group the samples into classes based on the grain size subject to the ratio of clay material in the rock fabric. The normal trend is observed for increase in shale content with smaller grain size. Based on the lithological description all the samples were grouped into three petrophysical classes then characterized by their own petrophysical relations and constants. This approach is based on the fact that the shave volume as opposed to grain size can be estimated from well logs and then applied to reservoir characterization and differentiation.