Experimental and numerical investigation of the impact of design parameters on the performance of WAG and SWAG injection in water-wet and mixed-wet systems

Experiments involving three-phase flow in porous media including Water-Alternating-Gas (WAG) injection are time-consuming andexpensive. Therefore, it is not feasible to experimentally consider all alternative injection schemes of these processes for different wettability and IFT (interfacial tension) conditions. The standard approach is to perform numerical simulations using models preferably tuned by laboratory data and experiments. We present the results of a series of two-phase (WF and GF) and three-phase (WAG and SWAG) coreflood experiments performed in both water-wet and mixed-wet rocks. The objective of the experiments was to understand the impact of wettability and injection strategy, as well as generating reliable data for tuning a simulation model. A numerical model was developed and validated via experimental results under both wettability conditions, and then used to investigate the effect of a large number of parameters including; WAG starting time and slugsizes well as oil/gas IFT and wettability on the performance of different injection scenarios. The results show that for water-wet systems, the highest oil recovery is achieved by SWAG (Simultaneous Water and Gas) and WAG injections and the poorest injection scheme is primary WF (water flood), whereas in the mixed-wet system, WAG and SWAG are the best and worst injection scenarios, respectively. In water-wet systems, the SWAG performance improved by increasing the ratio of gas to water while in mixed-wet systems, SWAG performance decreased by increasing gas to water ratio. Under water-wet conditions, better performance was achieved by smaller WAG slug sizes (higher number of WAG cycles) but for mixed-wet systems WAG performance decreased with increasing the number of the cycles. Our results also show that under near-miscible oil/gasconditions (IFT = 0.04 mN.m^-1), the oil recovery by primary GF (Gas Flood) was much higher for water-wet systems compared to the mixed-wet conditions. Although the same trend has been observed for the immiscible condition (IFT = 9.4 mN.m^-1), but under immiscible conditions the difference between the performance of GF for the two wettabilities(water-wet and mixed-wet) is not significant.For all oil/gas IFT values tested, WAG performance was found to be higher in mixed-wet systems compared to their water-wet counterparts, however, the effect of wettability was more pronounced in higher gas/oil IFT conditions. For both wettability conditions, starting WAG before water breakthrough of theprimary WF increased oil recovery.