EVALUATION METHOD AND APPLICATION OF FOAM DYNAMIC STABILITY IN HETEROGENEOUS CORES BASED ON NUCLEAR MAGNETIC RESONANCE TECHNOLOGY

Based on the conservation of effective pore volume and nuclear magnetic resonance technology, an evaluation method for the dynamic stability of foam in the cores was established. The oil and water calibration method was used to measure the volume of the oil phase and foam liquid in the cores, and the dynamic stability factor of the foam during the core displacement process was calculated. The transverse relaxation spectrum and nuclear magnetic resonance image of the double-layer heterogeneous core were tested. The oil displacement effect and dynamic stability factor of the nanoparticles-enhanced foam and the surfactant foam were compared. The results showed that the water phase volume in the core rose rapidly before 2.0 PV of foam was injected and then was basically stable; while the gas volume increased gradually, and the rising rate decreased after 5.0 PV of foam was injected. The dynamic stability factor of the foam had experienced three stages which was sharp decreasing, progressive increasing and stabilization. The oil displacement effect in the early stage of the foam mainly depended on the water phase. As the water phase volume was basically stable, the oil production rate of the cores had an obvious positive correlation with the growth rate of the foam dynamic stability factor, that was, the displacement of the remaining oil depended on the foam gas during middle and late stages. Compared with surfactant foam, nanoparticles-enhanced foam improved the sweeping capacity and oil displacement efficiency in the low permeability layer, inhibited the unstable stage of foam development and improved the final equilibrium value of the dynamic stability factor. The stability evaluation method could be used to reflect the characteristics of foam seepage and to screen stable foam systems suitable for reservoir characteristics.