Petrophysical criteria for differentiation of the Lower Carboniferous terrigenous sequence of the Republic of Bashkortostan

UDK: 553.98.061.32
DOI: 10.24887/0028-2448-2020-1-36-41
Key words: sandstones, siltstones, clay, petrophysical classes, well logs methods, electrophysical analysis
Authors: T.V. Burikova (RN-BashNIPIneft LLC, RF, Ufa), G.I. Minigalieva (RN-BashNIPIneft LLC, RF, Ufa), A.V. Dvorkin (RN-BashNIPIneft LLC, RF, Ufa), O.R. Privalova (RN-BashNIPIneft LLC, RF, Ufa), B.L. Khashper (RN-BashNIPIneft LLC, RF, Ufa), G.F. Baiburina (RN-BashNIPIneft LLC, RF, Ufa)

In the Paleozoic section of Bashkortostan the Lower Carboniferous terrigenous sequence is the largest hydrocarbon reserve. Significant oil accumulations in these deposits were discovered back in the 40s of the last century. However nowadays in Bashkortostan exploratory drilling has been actively conducted. So oil deposits discoveries replenished significantly. New licensed areas have not enough petrophysical information. So in this work the available geological and petrophysical information has been summarizing. The methodology of the work is based on a consistent study of data complex including detailed core study, lithotypes of rocks identification, comparing them with petrophysical heterogeneity and justification of factors affecting the reservoir properties. Mass clay can be used as a determining factor affecting the structure and filtration and capacitive properties of terrigenous rocks. All terrigenous differences were divided into three petrophysical classes according to boundaries selected by clay. For each class of rocks their own petrophysical dependencies are obtained and the boundary values of the filtration and capacitive parameters for reservoir identification were determined. Based on the core and well logs analysis results a lithofacial analysis has been carried out for electrofacies identification according to V.S. Muromtsev methodology. The filtration and capacitive properties distribution described by the petrophysical classes in accordance with the identified facies zones is shown, which gives an understanding of terrigenous deposits collector properties predicting possible accuracy by using lithofacial heterogeneity maps. So lithological heterogeneity of terrigenous rocks is revealed and confirmed. Proposed methodology also allows specify deposits geological structure when reservoir productivity predicting.


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