Visual in-situ monitoring of the behavior and phase states of water-hydrocarbon inclusions at high temperatures and pressures

Abstract

Experiments aimed at examining interactions between hydrothermal solutions and caustolithic rocks, oil, and its major fractions were carried out to obtain model water-hydrocarbon fluids (WHCF) and study their behavior and phase states at high P-T parameters. Simultaneously we experimentally synthesized and grew quartz crystals with inclusions as the major source of information on the behavior and phase state of the model WHCF. The inclusions were then examined with the application of conventional and local IR spectroscopy, gas and liquid chromatography, fluorescent and X-ray diffraction analysis, and the microthermometry of fluid inclusions. Interactions between hydrothermal solutions and caustolithic rocks were proved to result in the synthesis of an oil-like liquid, gaseous hydrocarbons (mostly methane), and solid bitumen. The behaviors and phase states of WHCF generated at temperatures below 260–320°C and above 330–500°C (under saturated vapor pressure and higher) were proved to be different, with these differences predetermined by oil cracking in hydrothermal solutions at temperatures above 330°C (particularly at 350–500°C) with the synthesis of predominantly light and intermediate hydrocarbon fractions. As the temperature was increased, the WHCF generated at temperatures of 260–320°C were transformed into two-phase oil-water fluids without free gas. In contrast to them, the heating of the fluids generated at 330–500°C first resulted in two-phase gas-liquid fluids with light oil fractions dissolved in them. As soon as the critical point (370–380°C) was reached, these fluids passed into a homogeneous supercritical state. The content of oil dissolved in hydrothermal weakly alkaline and alkaline solutions (visual estimations at temperatures of 260–400°C and pressures up to 90 MPa; the inclusions decrepitated at higher pressures) increased from a few hundredths and a few tenths of a percent to 8–10 vol % or, upon oil cracking at 380–450°C, to 20–30 vol % and more.