FEATURES OF THE FLUID REGIME OF POSTSEDIMENTOGENIC PROCESSES DURING THE FORMATION OF GAS CAPACITY OF THE TRANSCARPATHIAN BASIN (WITHIN THE LIMITS OF UKRAINE)

Abstract

Gases in migrating paleofluids of the Transcarpathian Basin in Ukraine proper were investigated. Their properties were analyzed using fluid inclusions in minerals and fluids occurring in closed pores of promising gas-bearing rocks. Samples were taken from wells drilled within the Mukachevo (1-Borodivsk-Novosilsk) and Solotvyno (1-Bushtyno, 4-Hrushovo, 1-Danylovo, 28-Solotvyno) depressions. According to the data from mass-spectrometric chemical analysis, methane and its homologues and carbon dioxide were found in the composition of volatile compounds, which coincides with the identified advantage of methane and its homologues, on the one hand, and carbon dioxide, on the other hand, in the natural gases of fields of the Transcarpathian gas-bearing area. Methane (98.2 vol. %), ethane (1.2 vol. %) and propane (0.6 vol. %) are found in fluid inclusions in calcite of veinlet in the rock from the well 28 of the Solotvyno structure, which includes the Solotvyno natural gas field. Only methane is found in closed rock pores. Natural gases of the Solotvyno gas field contain methane (53.86%), ethane (2.65%) and propane + butane (1.34-0.32%). СО2 contents as high as 97.3 vol. % occur in fluid inclusions in calcite of veinlets in rocks of the well 1 at Ruski Komarivtsi of the Mukachevo depression and 100 % in fluid inclusions in zeolite (?) from impregnates in rocks of the well 1 at Bushtyno of the Solotvyno depression. This can be explained by the activity of two different composition paleofluids, namely reduced or oxidating types present in bowels of the Transcarpathian Basin. They are associated with significant amount of reduced compounds (methane and its homologues) or a high concentration of oxidized compounds for their (mainly СО2). This was determined by differences in the composition of the primary high-energy abiogenic deep fluid: hydrocarbon-containing or carbon dioxide-containing. The gas composition of paleofluids indicates that two types of natural gas deposits may exist, mainly hydrocarbon or mainly carbon dioxide rich and, accordingly, the discovery of natural gas fields such as Solotvyno and carbon dioxide – such as Martovo. Hydrocarbon formation over a wide range of conditions and primary material ("oil polygenesis") allows the assessment of oil and gas resources of the region. A polygenetic approach for understanding hydrocarbon formation processes requires a changes in exploration strategy. More geochemical and thermobarometric research as well thermodynamic study of mineral-forming fluids is needed in promising geologic structures of the Transcarpathian gas-bearing area. This necessary, in order to predict possible occurrence of high-energy gas deposits and to determine areas for exploration.