Development of the diagenetic reservoirs in the Paleozoic carbonate deposits of the West Taimyr potential oil and gas bearing area

Introduction. The Paleozoic sedimentary series of the Enisey-Khatanga oil and gas bearing region has undergone a complicated geological history. Carbonate rocks composing significant volume of the strata show various traces of the secondary alterations that have both positive and negative effects on the reservoir properties of the carbonate rocks. Of particular importance in the exploration of oil and gas in carbonate depositional systems is the study of post-sedimentary changes in carbonate reservoirs and linking these changes with the stages of tectonic evolution of the region. This allows to solve the questions of reservoirs genesis and make conclusions about their spatial distribution. During the studies of the carbonate rocks in the first exploration well (Leskinsky license area on the left bank of the Enisey Bay) unique information was obtained on the composition and secondary transformations of Paleozoic carbonate reservoirs of the West Taimyr potential oil and gas bearing area.
Materials and methods. In the well the secondary dolomite reservoir rocks were described within several stratigraphic units; samples from that section were obtained for the detailed studies using a complex of instrumental methods. The samples were studied using standard optical (petrography and cathodoluminescence) microscopy, SEM-EDX, microtomography, data on stable isotope composition and thermobarometry of the twophase gas-liquid inclusions was obtained.
Results. The main intervals of the dolomite reservoirs were found in the Silurian — Lower Devonian and Emsian — Upper Devonian seismostratigraphic units (between reflecting horizons VII_bot и VIIa, VIa и VII, respectively). Silurian secondary porous and cavernous dolostones are dedicated to reef series. A system of well-connected secondary voids has formed over primary porous and well-permeable reef limestones. In the Emsian strata low-permeable limestones of shallow-deep subtidal were replaced by dolostones with separate vug porosity. Pore space here was formed due to fracturing and leaching of corals and stromatoporoid skeletons. The Upper Devonian dolostones were formed during the replacement of low-permeable microbial bindstones of the peritydal flat. For all the intervals diagenetic history was reconstructed and paragenetic diagrams were put together.
Conclusion. The results of the study of diagenetic dolomite reservoirs contain important information for predicting their distribution within the West Taimyr potential oil and gas bearing area.

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