Laboratory simulation and CO2 flooding efficiency of oil-water transition zones in a low permeability reservoir in the Jilin Oilfield

Abstract

Geological reserves of oil-water transition zone (OWTZ) in low-permeability reservoirs have been considered as uneconomical resources because of high water cut and low abundance. Though the OWTZ may account for 30 %–50% of a reservoir, it has not been paid more attentions yet. The average oil saturation of the OWTZ is about 35%, which is equal to that of a reservoir after water flooding. Currently, CO2 flooding is an effective technique for residual oil recovery after water flooding, which could reduce the residual oil saturation greatly. Therefore, it is of significance for the EOR of the low-permeability reservoir if the CO2 flooding could be successfully applied in the OWTZ. In this study, a method based on a long core to simulate distribution of oil saturation in OWTZs is set up in the laboratory using bidirectional saturation. In order to investigate CO2 flooding characteristics in OWTZs, experiments are carried out on 3 sets of initial oil saturation, and the recoverable reserves of the OWTZ and its contribution to the EOR are calculated based on the WJ reservoir in the Jilin Oilfield, China. Keywords: Oil-water transition zone, Initial oil saturation, CO2 flooding, Laboratory simulation, CT scanning