Abstract:

Based on the coring samples, injection water and formation water, optimized air foam, etc, from a typical tight oil block in Changqing oilfield, the 1D long core flooding system is utilized to carry out the experiments of injection capacity of pure foaming liquid, air and air foam into the core matrix and fracture. The experimental results indicate that under the real formation conditions, the air foam is not able to be injected into the tight core matrix directly, but because some of the foaming surfactant is absorbed by the reservoir rock, the defoamed liquid and air are able to flow into the tight core matrix and realized the stable displacement. According to the actual formation characteristics, three-core parallel flooding experiment is designed which include two matrix cores with permeability difference of 10 and one fractured core and the profile-controlling mechanisms by air foam are analyzed and determined. The air foam majorly flows into the fractured core and plugs the fractures, a part of defoamed liquid and air flow into the matrix cores to displace the waterflooded residual oil.Finally, the residual oil saturation of air foam flooding is 21.12% lower than that of waterflooding, and the oil displacement efficiency is 32.89% higher, which indicates encouraging performance following waterflooding. In order to avoid the inefficient production phase of ultra high watercut, it is recommended to convert to air flooding as early as possible before the water cut reaches 90%, so as to enhance oil rate and economic performance.

Key words: tight oil, air foam, permeability, displacement, fracture, oil displacement efficiency