Сверхкритические флюиды. Теория и практика
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2013, N2, pp. 39-60

V.S. Balitsky, G.V. Bondarenko, J. Pironon, S.V. Penteley, L.V. Balitskaya, M.A. Golunova, T.M. Bublikova

On the causes of vertical zoning in hydrocarbon distribution in earth interior: experimental evidences of crude oil cracking in high-temperature aqueous-hydrocarbon fluids

An experimental research was conducted to study the features of the hydrocarbons behaviour and their phase states at temperatures from 220 up to 500 °C and saturated vapour pressure and above (up to 150 MPa). The study was realized using the synthetic fluid inclusions in the quartz crystals which had been grown simultaneously with the interaction between the water solutions and crude oil. It was shown that the aqueoushydrocarbonic fluids generated at temperatures below 320 °C (approximate pressure of 30—50 MPa), depending on the thermobaric parameters and ratio of the water solution (L1), oil (L2) and the gas phase (G) (presented by water vapour), could exist as the three-phase (from L1>G≥L2 up to L2≥L1>G) and two-phase (from L1≥L2 up to L2≥L1) states. The cracking of oil in such aqueous-oil fluids is not observed. The fluids formed at temperatures above 330 °C (and especially at 380—450 °C) have higher amount of light oil fractions, gaseous hydrocarbons and residual solid bitumen. This means that the hydrocarbons in the hydrothermal systems are exposed to the cracking at the specified temperatures. Reheating of such multi phase inclusions to temperatures 240—280 °C leads to the complete dissolution of the liquid hydrocarbons in the gaseous and aqueous phases. Therefore, the fluid becomes bi phasic (water solution + gaseous hydrocarbons saturated by liquid hydrocarbons). The consecutive increase of temperature from 350 up to 380 °C transfers the fluid in homogeneous liquid or gaseous state, or in supercritical state. Fluid cooling results in its heterogenization, and all intermediate phases are consecutively restored. As a whole, the experimental studies confirm influence of the hydrocarbons cracking on the occurrence in the earth interior of the vertical zonal distribution of various types of the oil-and-gas deposits.

Key words: supercritical fluids, oil cracking, aqueous-hydrocarbon fluids, growth of quartz crystals, synthetic inclusions, oil, hydrocarbon gases, solid bitumen, thermobarogeochemistry of fluid inclusions

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