Prospects for oil and gas presence in carbonate deposits of Silurian age in the Berezhany-Buchach zone of tectonic dislocations of Volyn-Podillia area

Abstract

The Berezhany-Buchach zone of local uplifts belongs to the Podillia promising district, located in the southern part of the Volyn-Podillia oil and gas region. Most of the local structures of the district are genetically related to tectonic disturbances. The structuring factor of the Berezhany-Buchach zone of tectonic dislocations is a fault of subregional extension, probably of a reverse-thrust character. Organogenic structures of the Silurian age are spatially connected with it. According to the results of lithologic-facies studies, they were deposited in lagoon-shelf conditions in a narrow strip 15–40 km wide, which stretches from the border with Romania in the southeast to the border with Poland in the northwest. According to the predominance of the remains of organisms, coral, stromatopore, crinoid, ostracod, brachiopod and algal species are distinguished among carbonates. They are recrystallized as a result of epigenetic processes. The reservoir rocks are composed of silty-detrital limestones, dolomitized limestones, and dolomites. There are both porous and cavernous, as well as fissure-pore and fissure-cavern collectors. Primary porosity is caused by voids inside and between organisms, and secondary capacity is caused by recrystallization, dolomitization, leaching, cavernous and fissure formation. The open porosity of carbonates varies on average from 4 to 16 %, permeability – from 0.01 to 2 mD. In the southeastern direction, the collector properties of carbonates deteriorate. Industrial deposits of hydrocarbons in the Silurian carbonates of Volyn-Podillia have not been established, however, numerous oil and gas occurrences were recorded during drilling. Based on the materials of lithologic and facies studies, the results of studying the reservoir properties of reservoir rocks, seismological and magnetometric constructions, and data from surface geochemical studies, the probable Berezhany, Dobrovoda, and Buchach objects were identified, their resource base was estimated at 48.6 million tons of oil and 1.3 billion m3 of dissolved gas, and the tasks for 3D seismic exploration were substantiated for the purpose of preparing the mentioned objects for exploratory drilling for oil and gas.