Petrographic and petrophysical features of the pre-Jurassic volcanogenic deposits of the Krasnoleninsky arch of Western Siberia

A significant volume of hydrocarbon reserves identified in the pre-Jurassic basement of the Krasnoleninsky arch in Western Siberia is associated with volcanic deposits, which are characterized by a variety of rock types. The petrographic and petrophysical features of these rocks determine their ability to host reservoir fluids. Structural and textural features are determined both by the surface conditions of origin of their formation and secondary alterations. Petrophysical parameters are determined by the material composition and structural-textural features of petrotypes. The average mineralogical density of acidic volcanites is 2,64 g/cm3, with a range of 2,58-2,69 g/cm3. Mineralogical density increases from acidic volcanites to basic volcanites up to 2,79 g/cm3. Porosity and permeability coefficients decrease in this direction, except for a few samples of volcanogenic-sedimentary rocks and medium-composition volcanites. Basic volcanites and terrigenous rocks are non-reservoirs. Porosity and permeability of volcanites increase from lavas to volcanic rocks. At the same time, decompacted lavas have greater porosity and permeability than massive-textured lavas. The conditional boundary between lavas and volcanic rocks in terms of porosity and permeability corresponds to: porosity – 0,12 units, permeability – 0,15·10-3 mkm2. Transformed volcanites occupy an intermediate position between lavas and volcanic rocks. The analysis of petrographic features and petrophysical properties showed that lavas (decompressed varieties), volcanic rocks and transformed volcanites of acidic composition, and much less frequently, volcanogenic-sedimentary rocks and volcanites of intermediate composition are promising in the prospect of their reservoir properties.

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