Coefficient of Gas-Oil System Under High Temperature and High Pressure

As the technology of enhanced oil recovery by gas injection has already been applied worldwide, the research of the transmit mechanism between injected-gas and oil is important to the optimization of gas injection plan. Diffusion is an important phenomenon during the process of gas injection displacement. Because of diffusion, gas molecules will penetrate into the oil phase, while the oil will penetrate into the gas phase. Oil and gas could get balance with time. Diffusion affects the parameters of system pressure, component properties and balance time, which thus affect the efficiency of displacement. Molecular diffusion, which we usually refer to, includes mass transfer diffusion and self-diffusion. Mass transfer diffusion mainly occurs in non-equilibrium condition of the chemical potential gradient ( i  ) .The moleculars move from high chemical potential to low chemical potential of molecular diffusion until the whole system reaching equilibrium. The self-diffusion refers to free movement of molecules (or Brownian motion) in the equilibrium conditions. Mass transfer diffusion and self-diffusion can be quantitatively described by the diffusion coefficient. Up till now, there is no way to test the molecular diffusion coefficient directly. As for the question how to obtain the diffusion coefficient, it is a requirement to establish the diffusion model firstly, and then obtain the diffusion coefficient by analysis of experiments’ results.