Influence of crude oil cracking on distribution of hydrocarbons in the Earth’s interior (experimental data)

The compositions and phase conditions of water-hydrocarbon fluids in synthetic quartz inclusions were studied by the methods of microthermometry, local IR spectroscopy, and gas-liquid chromatography. Synthetic quartz was grown in near-neutral fluoride, low-alkali bicarbonate, and alkali carbonate solutions with crude oil and its major fractions. The crystals with fluid inclusions were grown under thermal gradient conditions at relatively low temperatures (240–280°C) and pressures (6–45 MPa). After the study, the inclusions of grown crystals were subject to thermal processing in autoclaves at 350–380°C and 80–125 MPa. As a result, the initial water-hydrocarbon inclusions underwent significant changes. Hydrocarbon gases, largely methane and residual solid bitumens, appeared in their composition; the gasoline-kerosene fraction content increased substantially in liquid hydrocarbons (HCs). These changes are caused, first of all, by crude oil cracking, which is manifested already at 330°C and attains its maximum activity at 350–500°C (pressure of saturated vapor and higher). In natural conditions with increase in depths and, thus, the thermobaric parameters, this process is inevitable. According to the obtained experimental data, this very phenomenon and the existence of real thermal and baric gradients in the Earth’s interior provide for the formation of vertical zoning in the distribution of hydrocarbon deposits of different types.     

Phase states of hydrous–hydrocarbon fluids at elevated and high temperatures and pressures: Study of the forms and maximal depths of oil occurrence in the Earth’s interior

Based on synthetic fluid inclusions in quartz grown at 240–490°C and 7–150 MPa in aqueous–oil solutions, the behavior, composition, and phase states of liquid, gaseous, and solid hydrocarbons (HC) were studied. Investigations were performed using common and fluorescent microscopy, microthermometry, local common and high-temperature IR Fourier spectroscopy, Raman spectroscopy, chromatography, and X-ray and microprobe analysis. The data obtained allowed us to understand the influence of thermobaric conditions and volume proportions of the oil, aqueous, and gaseous phases on the composition, phase state, and behavior of hydrous–hydrocarbon fluids and estimate the forms and probable maximal depths of the origin of oil in the Earth’s interior.     

Behavior of oil in interactions with aqueous solutions under elevated and high temperatures and pressures

The behavior of oil was studied, and the solubility of its light and heavy fractions in hydrothermal solutions was evaluated at 260–700°C and pressures of 30–200 MPa. The experiments were accompanied with simultaneous growth of quartz crystals containing fluid inclusions (in the same solutions). These inclusions allowed one to trace, by means of thermobaric geochemistry, the in situ behavior of oil within a wide range of temperatures and pressures. It was shown that the oil undergoes pronounced transformations under the interactions with hydrothermal solutions. Even at 260–300°C (pressures of 30–50 MPa), the oil was enriched in light fractions. The content of these fractions was pronouncedly increased at 330–350°C (70–80 MPa pressure). This process was accompanied by the appearance of mazut-like, semisolid, and solid bitumoids in amounts that increased manifold within the 400–700°C temperature range (up to 200 MPa pressure). The oil transformations were accompanied by an ample emission of methane. At 260–300°C, the oil in the hydrothermal solution occurred mainly as liquid drops. However, at temperatures near 400°C (about 100–150 MPa pressure), the solubility of light fractions increased to about 5–6 vol % which pointed to the ability to transfer significant amounts of oil not only in the liquid-drop form but also in the dissolved form.