Conditions of formation of oil deposits in flysch sediments at the north-western part of the Pre-Carpathian foredeep

Abstract

The research has shown that in the Inner Zone of the Pre-Carpathian foredeep as a whole and the Boryslav oil field in particular, oil and gas condensate fields are located naturally due to the spread of deep faults within. It is established that oil and gas deposits of fields represent a set of sand lenses within a certain complex of flysch rocks, the increased oil saturation of which is associated with fracture. The obtained results showed that the oil deposits in Boryslav sandstone have a lenticular structure, and the high productivity of wells is associated with the vein form of hydrocarbons in the sand layers. In order to determine the nature of productivity Boryslav sandstone, we modeled a map of integrated oil production from deposits in Boryslav sandstone from Boryslavska deep fold, which shows all the wells that opened this layer. It is established that in the area, which covers only 0.8 of the area of Boryslav sandstone (eastern part of the field), from the wells that exploit it, extracted 15% of the total oil production from the Boryslavske field as a whole. At the same time, the distance between the most productive wells is only 110 m. Also, on the same site between high-performance wells at a distance of only 50-100 m there were also those in which from Boryslav sandstone oil inflows were not received at all. It is characteristic that industrial inflows of oil are received from small intervals (1-2 m) in the cross-section of 20-30 m of a powerful sandy horizon. The intervals of tides could be both in the roof and in the plantar part or in the middle part of the formation. While in some areas and even in the vaulted part of the folds (theoretically the most promising for anticlinal folds) tides are not obtained at all. We believe that for effective exploration of Boryslav oil field it is necessary to change its methodological basis. Namely, exploration wells must be drilled based on the location of wells that gave an industrial influx of oil, placing them gradually at short distances.

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