Tectonic units of the Krosno (Silesia) cover of the Folded Carpathians: Tykhiy (Ukraine) and Vetlina (Poland) structures – geological structure and gas-bearing potential

Abstract

In the south-western part of the Krosno cover in the terrain of the Ukraine, that is called jednostka Szląska (Silesia Unit) in the adjoining Polish territory, two tectonic structures Tykhiy and Vetlina composed of flysh of the Cretaceous-Paleogene age, are correspondingly present. They are in the same scale and represent preserved anticlinal fold of the north-western strike. The Tykhiy and Vetlina structures were defined according to results of drilling. In consequence of executed drilling works the commercial gas presence of both structures was determined. Maximum gas discharges from the deposits of Oligocene at both structures are estimated to be approximately 60th m3/day. The production reserves of the Vetlina structure are estimated at 73 million m3 of gas. The deposit is not being developed due to localization in the area within the Beskydy National Park. The authors don’t recommend to carry out exploratory drilling within the limits of the structure, in located further north-east of the Tykhiy structure the Volosianka–Pidpolozzia and Husne–Bukovets scales as the ineffective drilling because of the absence of perspective objects in their composition. There are prerequisites to suppose the presence of just one more gas-saturated fold, Liuta, further south-west of the Tykhiy structure, under the Duklya–Chornohora cover. It is located within the hydrocarbon field, favourable for the search for hydrocarbons. The potential industrial gas potential of the forecasted promising structure is evidenced by the inflows of oil and gas in the mapping wells of Liuta Square. Significant manifestations of hydrocarbons were observed in well 18-Liuta. From a depth of 40 m, and then 190 m recorded oil manifestations – oil films on the surface of the clay solution (d 20 – 0.843 g/cm3; viscosity in 0E – 1.92; S – 0.22 %, the beginning of boiling – 97 °C, up to 350 °C – 56 %). Intense gas manifestations were noted from a depth of 167 m (CH4 – 95.36 %; CO2 – 1.01 %; N2 – 3.63 %). To check this supposition, it is expedient to conduct seismic survey.