Key words: supercritical fluids, oil cracking, aqueous-hydrocarbon fluids, growth of quartz crystals, synthetic inclusions, oil, hydrocarbon gases, solid bitumen, thermobarogeochemistry of fluid inclusions
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.
doi:10.1134/S1990793114070045