Nitrogen is used in both the miscible and immiscible gas injection processes in oil reservoirs. In heterogeneous formations, gas tends to early breakthrough due to overriding and fingering. Surfactant alternating gas (SAG) injection is one of the methods commonly used to solve this problem. The foam which is composed in contact area of nitrogen and surfactant, increases injected gas viscosity. However, adsorption of surfactant on rock surface can increase cost of process. This work describes theexperimental study of SAG injection versus water alternating gas (WAG) and water flooding. In this study the concentration of surfactant was optimized to minimize adsorption of surfactant on rock surface which lower the cost of surfactant. Results show that using the concentration of 1500 ppm of surfactant solution is economically cost effective. Results also shows that the SAG ratio of 1:1 with rate of 0.2 cc/min at temperature and pressure of 70°C and 144.74×105 Pa, has the maximum oil removalefficiency. In this SAG ratio, stable foam was formed and viscous fingering delayed in comparison with other ratios. Finally, this study demonstrated that SAG injection has higher oil recovery in comparison with other displacing methods (water flooding, gas flooding and WAG).
Key words: Surfactant alternating gas (SAG), cycle ratio, foam, sand pack, spectrophotometer.
Abbreviations: SAG, Surfactant alternating gas; WAG, water alternating gas; BPR, back pressure regulator; API, American Petroleum Institute; SDS, sodium dodecyl sulfate; PV, pore volume; SO, safranin O; S.S, surfactant solution; OOIP, original oil inplace; MMP, minimum miscible pressure.
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