Synthesis and performance evaluation of high stability foaming agent for air foam flooding

The pores in low permeability reservoirs are structurally complex with large surface area, so the adsorption loss of foaming agent in reservoirs is serious in the process of air foam flooding and consequently the application effect of air foam flooding is impacted. The reservoirs in Ganguyi Block of eastern Yanchang Oilfield are of low porosity (average 10.76%) and extra low permeability (average 0.933 mD). In order to reduce the adsorption of foaming agent to the reservoirs and increase the stability of foam solution, a new kind of anionic surfactant foaming agent based on aliphatic alcohol polyoxyethylene ether-phthalic acid ester sodium salt was developed according to the actual geological characteristics of the oil reservoirs. Then, its basic performance was evaluated systematically, e.g., foamability, tolerance to high temperature and salt, adsorption loss, oil resistance, and interfacial tension. And the following research results were obtained. As for the stability, the foam height is over 180 mm when the concentration of foaming agent is more than 2 000 mg/L, and the foamability of the new foaming agent is superior to that of sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (ABS) in the case of 2 000 mg/L and 30 ℃. Speaking of the stability in presence of oil, the foaming is slightly interfered if foam occurs after the crude oil is added with the dosage less than 20%. If the crude oil is added after the foaming, the stability of the foam is still better when the dosage is 20%. It is revealed that the new foaming agent is much better than the ABS and the BK6A adopted in foam flooding system of Ganguyi Block in term of stability in presence of oil. As for the adsorption loss, the foaming volume decreases from 620 mL to 590 mL when 25 g oil sand is added. Obviously, the adsorption amount is small. The excellent foamability, foam stability and tolerance to high temperature and salt of new foaming system provide the important substantial basis for foam flooding agent system. It is not only suitable for the extra low permeability oil reservoirs in the shallow layers in eastern Yanchang, but also for the extra low permeability oil reservoirs in the middle and deep layers in western Yanchang.