Factorial two-stage analyses of parameters affecting the oil–gas interface and miscibility in bulk phase and nanopores

In this paper, a factorial analysis approach is applied to characterize the potential single and interactive factors as well as their effects on the interface and miscibility of three light oil–CO2 systems under 32 different conditions. First, a modified Peng–Robinson equation of state coupled with the parachor model is applied to calculate the vapour–liquid equilibrium and interfacial tensions (IFTs) at a variation of pore radii and different pressures, based on which the MMPs are determined from the diminishing interface method. Second, by means of the factorial-analysis approach and calculated IFTs and minimum miscibility pressures (MMPs), the following five factors are specifically studied to evaluate their main and interactive effects on the IFTs and MMPs: temperature, initial oil and gas compositions, feed gas to oil ratio (feed GOR), and pore radius. It is found that the main and interactive effects of the five factors on the IFTs are inconsistent at different pressures. The effects of the five factors on the MMPs are evaluated quantitatively, which contribute to screen out significant factors, analyze interactions, and identify schemes for the miscible CO2 enhanced oil recovery. The most positive significant main and interactive effects on the MMPs are Factors C (gas composition) and AB (temperature and oil composition), whereas the most negative results are Factors E (pore radius) and AC (temperature and gas compositions). A three-factor analysis indicates that the MMP is substantially reduced in small pores by controlling the percentage of the CH4-dominated gas in the impure CO2 sample and lowering the feed GOR