Application of Lithological and Geochemical Approach to Determine the Genesis of Dolomite Cavernous Reservoir (Lower Devonian, Gydan Peninsula)

To evaluate the origin of cavernous hydrocarbon reservoir in the Lower Devonian dolostones (Western Taimyr, eastern coast of the Gydan Peninsula), the host rocks and the infilling carbonate minerals were studied using an integrated approach, including petrographic, cathodoluminescence, isotopic, geochemical and fluid inclusion studies. This approach showed that limestones that accumulated in the open subtidal shelf zone underwent dolomitization in early diagenesis, and dolomites with a fine-crystalline matrix were formed; the dolostones were significantly compacted during subsequent subsidence and geostatic compaction. The dolostones underwent fracturing the Late Hercynian tectonic phase (Late Carboniferous – Permian); fractures are associated with fissure caverns. Both fractures and caverns are partially filled with high-temperature generations of dolomite, quartz and calcite; low negative δ18о values and high positive Eu/ Eu* anomalies confirm their hydrothermal genesis. Similarity in PAAS-normalized patterns of Rare Earth Elements in the host rock and vein (cavernous) carbonate mineral indicates that the source for the infilling carbonate was the host rock. The results obtained show the high potential of using the applied approach in establishing the stages of development of a carbonate reservoir and for predicting its distribution in the section and area.