Oil Recovery by Near-Miscible SWAG Injection

Abstract

Abstract We present micromodel visualization of pore-scale displacement mechanisms and fluids distribution during recovery of residual oil by near-miscible Simultaneous-Water- And-Gas (SWAG) injection under conditions of very low gas-oil interfacial tension (IFT) and negligible gravity forces. A 3- phase fluid system with gas-oil IFT of 0.08 mN/m, representing a near-miscible fluid system, together with high-pressure (5100 psia) micromodel were used for the flow experiments. We demonstrate that in near-miscible SWAG injection, the oil recovery continues significantly and almost all of the oil that has been contacted by the gas will be recovered, after the main gas breakthrough. This oil is recovered by a microscopic mechanism, which is strongly linked to the low IFT between the oil and gas and to the perfect spreading of the oil over water, both of which occur as the critical point is approached. We have performed experiments with different SWAG (gas/water volumetric) ratios and we show that the ultimate oil recovery during SWAG injection is almost independent of SWAG ratio, within the tested range of 20 to 50%. This makes SWAG injection an attractive IOR process especially for reservoirs where continuous and high rate gas injection is not possible (e.g. due to supply constraint). In oil reservoirs that cannot export gas (remoteness from the market) WAG (for abundant gas volume) or SWAG (for low or high volume of gas) can be implemented.