The Tertiary FAWAG Process on Gas and Water Invaded Zones: An Experimental Study

Abstract

In this research, experimental investigations of foam-assisted water alternating gas and water alternating gas processes in carbonate cores are studied in order to estimate the increases in the oil recovery in the gas and water invaded zones. Core flooding experiments were performed for low-temperature fractured carbonate cores, chosen from one of the Iranian carbonate oil reservoirs, under tertiary recovery conditions. The experiments were conducted on 1.5-in. diameter carbonate cores, using live oil and synthetic/field brine (with 5,000 ppm of salts) as the water formation and also sodium lauryl sulfate as an anionic surfactant along with pure CO₂ as the injection gas. The samples were initially saturated with live oil and connate water and then flooded with brine to reach residual oil saturation at reservoir conditions (115°F and 1,700 psia) to imitate the water invaded zone in the core. In addition to that, since the reservoir has a secondary gas cap, the same procedure was used to provide the gas invaded zone with methane as well. After performing water and gas flooding processes, several cycles of foam-assisted water alternating gas and water alternating gas were injected into the core. The experimental results indicated that a better swept efficiency and, consequently, a higher improved oil recovery can be achieved by the foam-assisted water alternating gas process. The recoveries are shown to be 19.2 and 28.7% of the residual oil in place for gas and water invaded zones, respectively. Furthermore, the results indicate that in the foam-assisted water alternating gas process, the produced free gas decreases due to foam generation inside the core.

Keywords:

• core flooding
• foam-assisted water alternating gas process
• gas invaded zone
• minimum miscibility pressure (MMP)
• surfactant
• water invaded