Origin and migration of oil from the Ukrainian Outer Carpathians to their Mesozoic basement: the case of the Lopushna traps

Abstract

1 Na tional Acad emy of Sci ences of Ukraine, In sti tute of Ge ol ogy and Geo chem is try of Com bus ti ble Min er als, Naukova 3a, 79060 Lviv, Ukraine The Lopushna oil field has been dis cov ered in Mesozoic-Paleogene strata of the plat form base ment be neath the Ukrai nian Outer (Flysch) Carpathians. Oils from two main ac cu mu la tions, oc cur ring in Up per Cre ta ceous sand stone and Up per Ju rassic lime stone res er voirs, have been ana lysed in or der to iden tify their or i gin and re la tion to the known pe tro leum sys tems in the re gion of the Outer Carpathians and the base ment of the Carpathian Foredeep. Re sults of geo chem i cal in ves ti ga tions of oils, in clud ing biomarker and iso to pic data, show a good cor re la tion with oils ac cu mu lated in Carpathian flysch strata. The oils are low-sul phur and did not un dergo sig nif i cant deg ra da tion. They were gen er ated from Type II or II/III kerogen, de posited in anoxic en vi ron ments in clastic sed i ments. Gen er a tion oc curred at the peak of "oil win dow", prob a bly in the tem per ature range of 122 to 126 o C. The pres ence of oleanane in di cates Cre ta ceous or youn ger source rocks. Good cor re la tion of biomarker and iso to pic data with the or ganic mat ter dis persed in the Oligocene Menilite Beds oc cur ring at the top of the Carpathian flysch suc ces sion al lowed iden ti fi ca tion of these as source rocks for oils of the Lopushna field, which thus can be re garded as an oil fam ily of the Outer Carpathians. The mi gra tion dis tance for both the Lopushna oils and oils ac cu mu lated in the Carpathian flysch strata was sim i lar. A num ber of sub-ver ti cal dis lo ca tions, along which the sub sided flysch strata oc cur at the same depth level as the Ju ras sic and Cre ta ceous rocks of the plat form, can be as sumed as pos si ble mi gra tion pathways from the ma ture source rocks of the Oligocene Menilite Beds of the Boryslav-Pokuttya, Skyba or Krosno units to the Lopushna type traps, which sug gests the pos si bil ity of ex is tence of other hy dro car bon ac cu mu la tions of this type. The Lopushna field so far is unique in con tain ing this type of oil found in the base ment of the Ukrai nian Carpathian Foredeep.

Burial and Thermal History Modeling of the Paleozoic–Mesozoic Basement in the Northern Margin of the Western Outer Carpathians (Case Study from Pilzno-40 Well, Southern Poland)

“…In the Austrian part of the Alpine fold-and-thrust belt, hydrocarbon migration from sub-thrust Oligocene source rocks into the undeformed foreland Cenomanian reservoirs by the fault system has also been emphasized [7]. The possibility of filling the reservoirs in the Mesozoic basement with the hydrocarbons generated within the Carpathian flysch strata suggests that other structures similar to the Ukrainian Lopushna field may have accumulated hydrocarbons, and that new discoveries of such fields are possible [99].…”