Experiments on thermal miscible rules of different gas media and crude oil

The high temperature and high pressure visualization pressure-volume-temperature (PVT) experiments of different gas media-crude oil were carried using the interface disappearance method. There are two miscible temperature domains in the miscibility of CO₂-crude oil during heating process under constant pressure. Under the experiment pressure of 15 MPa, when the temperature is less than 140 °C, the miscible zone shows liquid phase characteristics, and increasing the temperature inhibits the miscible process; when the temperature is greater than 230 °C, the miscible zone tends to show gas phase characteristics, and increasing the temperature is conducive to the miscibility formation. Under a certain pressure, with the increase of temperature, the miscibility of flue gas, nitrogen and crude oil is realized. When the temperature is low, the effect of CO₂ on promoting miscibility is obvious, and the order of miscible temperature of gas medium and crude oil is N₂ > flue gas > CO₂; however, when the temperature is high, the effect of CO₂ on promoting miscibility gradually decreases, and the miscible temperature of N₂ and crude oil is close to that of flue gas. The miscibility is dominated by the distillation and volatilization of light components of crude oil. There are many light hydrocarbon components in the gas phase at phase equilibrium, and the miscible zone is characterized by gas phase.