Lithogeochemistry of black shales of the Phanerozoic of the Western Ukraine ‒ unconventional hydrocarbon reservoirs

Abstract

The purpose of this work is to compare the lithological, geochemical and mineralogical features of carbonaceous clayey and siliceous-clay rocks of Cretaceous-Paleogene flysch of the Ukrainian Carpathians and Lower Silurian of the Volyn-Podillya edge of the East European Platform and to determine the factors that contributed to the formation of zones of “unconventional reservoirs” in these sedimentary strata of cracked and mixed types. Data from the lithology, geochemistry and mineralogy of bituminous siliceous-clay rocks and siliceous rocks of Lower Cretaceous and Oligocene of the Carpathians and black argillites of Lower Silurian of the Volyn-Podillya edge of the East European Platform are presented. Sedimentogenesis of Lower Cretaceous and Oligocene bituminous deposits of the Carpathians and Lower Silurian deposits of Volyn-Podillya took place in anoxic conditions (phases of oceanic anoxic events: OAE-1 (Barrem–Albian), OAE-4 (Oligocene) and at the border of Ordovician and Silurian. Paleoceanographic conditions of their sedimentation differed significantly. The first are deep-sea formations at the foot of the continental slope of the Carpathian segment of the Tethys Ocean, the second were accumulated in the warm shallow sea on the eastern shelf of the West European Sea Basin. The layered texture of carbonaceous deposits, as well as the catagenetic transformation of rock-forming clay and siliceous minerals and their hydrophobization, played a significant role in the formation of the filtration capacity properties of “unconventional reservoirs”. In Cretaceous-Paleogene flysch deposits of the Carpathians, “unconventional reservoirs” are usually terrigenous-clay or siliceous-clay rocks with shale and layered texture or compacted sandstones localized in conventional oil, gas or condensate deposits. Lower Silurian clay deposits of Volyn-Podillya are promising for the search for “shale gas”.