Research On Foam Flooding With Low Gas-Liquid Ratio For Conventional Heavy Oil

Compared with the conventional reservoir, the recovery of the heavy oil reservoir is at least 10% lower than that of conventional reservoir. The high oil mobility ratio of heavy oil leads to the low sweep efficiency, so it is more important to improve sweep efficiency than microscopic displacement efficiency for the EOR technology suitable for heavy oil reservoir. Previous researches have proved that foam flooding can increase the sweep efficiency and control gas mobility, and thus increase oil recovery. However, its application was restricted due to the high cost and injection pressure, so foam flooding with low gas-liquid ratio(GLR) was proposed to enhance the heavy oil recovery.Two foaming systems with good foaming ability and low interfacial tension were selected. The first included 0.2wt% DS and 0.5wt% Na2CO3, the other included 0.2wt% DS, 0.5wt% Na₂CO₃ and 0.1wt% partially hydrolyzed polyacrylamid (HPAM).In core test, taking Zhuangxi heavy oil (325 mPa·s at 55℃) as the object, a series of experiments were performed by increasing the gas-liquid radio incrementally from 0.1:1 to 2:1,it shows that when the gas-liquid ratio is below 0.5:1, the oil recovery increases drastically with the increase of the gas-liquid ratio of foam flooding. When the gas-liquid ratio is above 1:1, the increase of gas-liquid ratio results in only a small incremental recovery. Foam flooding with gas-liquid ratio of 0.2:1 improves oil recovery by about 18.1%, which is 8% higher than alkaline and surfactant flooding under the same conditions. It indicates that the low gas-liquid ratio still results in a good EOR effect. In sand pack tests, polymer enhanced foam flooding improves the oil recovery by 39.8%, which is 11% higher than ASP flooding under the same conditions. And the tertiary oil recovery decreased with the increasing viscosity of crude oil. Polymer enhanced foam flooding in the plate model shows that polymer enhanced foam system has excellent profile modification effect to increase sweep area, it can improves recovery by about 30%.It is discovered by microscopic visual technique that there are two important characteristic of the improving sweep efficiency mechanism of foam. One is that the foam passes the pore throat one by one so there are no foam bridging and plugging. The other is that when foam passes the pore throat foam is deformed, the better elasticity of the foam the bigger resistance due to the extrusion deformation. Moreover, it is discovered by microscopic visual technique that foam is more stable in heavy oil than in light oil.These results confirm that low gas-liquid ratio foam flooding is a promising method for developing conventional heavy oil for its low cost and high recovery. Cost of this technology can be reduced by at least 50% compared to the conventional foam flooding (gas-liquid ratio ranges from 0.5:1 to 1:1).