Experimental study on residue oil distribution after the supercritical CO2 huff-n-puff process in low permeability cores with Nuclear Magnetic Resonance (NMR)

Abstract

In this paper, two sandstone cores with permeabilities of 1.7mD and 2.6mD were employed and the ScCO2 huff-n-puff processes were carried out to check the oil recovery efficiency as well as the oil mobilization laws under the conditions of 50 °C and 25 MPa. Both cores were cut half after the completion of the process and the residue oil distribution in the entire core as well as the front half and back half of the core were scrutinized with help of the Nuclear Magnetic Resonance (NMR) measurements. It is found longer soaking time of 5 days leads to higher oil recovery rate of 17.2% in comparison with 15.2% after 1 day’s operation time. NMR measurement results show that more oil in the large pore spaces of the core is produced, while the oil in the small pore spaces is rarely mobilized after the ScCO2 huff-n-puff process. NMR results further show that the oil saturation in the large pores of the front part is obviously lower than that of the back part of the core, which indicates that a round of huff and puff operation mainly produced the oil in the large pore spaces from the front part of the core, while leave a considerable part of the oil undeveloped in the rear part of the core.