LITHO-STRATIGRAPHIC FEATURES OF THE LOWER CRETACEOUS DEPOSITS OF THE SKYBA AND DUKLA-CHORNOGORA NAPPES OF THE UKRAINIAN CARPATHIANS AND PROSPECTS FOR THEIR OIL AND GAS POTENTIAL

Abstract

Lower Cretaceous sediments are widespread within the Skybа and Dukla-Chornorgora Nappes (Spas and Shypot Formations) over a considerable area. These deposits contain sandstones that can be industrial reservoirs for hydrocarbons. Such sandstones are described both on the surface and identified in deep wells. Thick sandy strata in the middle part of the Spas and Shypot formations formed as deposits of gravity flows at the second level of avalanche sedimentation, at the foot of the continental slope of the northern continental margin of the Tethys Ocean. Their formation is correlated with global regression in Aptian time. Porous sandstones of the Spas formations are present on the surface in the areas of the villages of Tershiv and Busovysko. They sometimes form bundles up to 60 m thick. They are exposed in the Oryv and Berehyv Skybas by deep wells 1-Lugy, 1-Shevchenko, and 4-Maksymivka. During the drilling of the 1-Shevchenko well from a depth of 6,900 meters, a film of oil and gas continuously flowed into the drilling mud. According to the results of industrial and geophysical studies, the section of the Spas formations of the second (lower) scale in the interval of 6,940–7,520 m was recognized as the most promising in terms of oil and gas potential. Two promising objects in the intervals of 7020–7070 and 6945–6985 m were identified, the oil and gas saturation coefficients of which are 65–70%. Similar sandstones are noted in the Hoverla sub-Nappe of the Dukla-Chornogora Nappe along the Balzatul River and its tributaries (Bila Tysa River Basin) as part of the Shypot Formation. Sandstones with an open porosity of 8–12 % were identified in the 1-Hrynyava and 1-Semakiv wells in the deposits of the Shypot Formation of the Skupiv sub-Nappe according to the results of industrial-geophysical research. When testing them in the 1-Semakiv well, from the total interval of 473–569 m, they received inflows of combustible gas and light oil with flow rates of 3,000 m3/day and 2.64 m3/day, respectively. The analyzed materials testify to the prospects of the Spas and Shypot formations in relation to the discovery of industrial accumulations of hydrocarbons.