Gravity-Stable Nitrogen Displacement of Oil

Abstract

Abstract A series of experiments to investigate secondary and tertiary, gravity stable, immiscible, nitrogen displacement of oil in the presence of connate water is presented. Both high and low pressure experiments have been conducted using water wet sandstone cores and dead oils. Effluent production was recorded and the spatial distribution of oil along the core was determined using a radioactive tracer technique. Experimental results are presented for secondary nitrogen injection at different flow rates, connate water saturations and core orientations. In-situ saturation measurements in a low pressure experiment have revealed a residual oil saturation to gas of 0.15 after 68 days of drainage. The results of a tertiary nitrogen injection experiment at low pressure are presented. The residual oil saturation to water flooding was 0.47. During the tertiary gas flood, an oil bank was observed to develop and the oil saturation decreased to 0.08 after 86 days of gas flooding. This experiment demonstrates that tertiary gas injection can result in significant oil production, even at low pressures where the process is expected to be least efficient. Oil relative permeability data have been derived from the in-situ saturation measurements and permeabilities down to 10-5 observed.