Nitrogen assisted artificial foamy oil flooding (AFO) is an oil recovery process in which nitrogen and foamy oil agent are injected into a water flooded reservoir to drive the remaining oil when it is emulsified with the injected gas and water. The rheological behavior of the emulsified oil is similar with foamy oil flow, so this process is called artificial foamy oil flooding in this paper.
A visible micro-model of etched glass is developed to observe the emulsification process of nitrogen, foamy oil agent, water and oil. The foamy oil agent is a composition of surfactants like foaming agents, foam stabilizers, viscosity reducers and so on. One-dimensional flooding experiments are conducted to measure the resistance factor of artificial foamy oil flow process. The impacts of foamy oil agent concentration and air/liquid ratio upon the resistance factor are assessed in the experiments too. The potential of AFO of overcoming the interlayer interference effect is evaluated with parallel core flooding experiments. Based on experimental results, the reservoir engineering aspects of this technique is discussed and the capability of enhancing oil recovery is demonstrated with a pilot application outcomes.
The mechanisms of AFO unveiled with the etched glass model include: (1) dramatic viscosity reduction with oil/water emulsification; (2) increased elastic energy of oil saturated with micro gas bubbles; (3) Foam blockage in water saturated zones; (4) improvement of drainage factor with pseudo miscible flooding. Compared with the simple treatment with viscosity reducer, AFO is more stable which does not separated within four hours. It reduces the oil viscosity by 80%. The resistance factor can be as high as 58 when the concentration of foamy oil agent is 0.5%. Parallel core flooding experiments reveal that the injection of nitrogen and foamy oil agent after water flooding can reduce water cut by 12%, and enhance oil recovery by 15.8%. In the pilot in Tuha Oil Field, PetroChina, the injected nitrogen compensated the formation pressure rapidly and emulsified with oil to stimulate daily oil production rate and recovery. Demonstrated with reservoir engineering theories and numerical simulation, whose outcomes are compatible with the pilot performance, artificial foamy oil flooding is of great potential to further enhance oil recovery for water flooded reservoirs in Tuha field.
Artificial foamy oil flooding technique, inspired by foamy oil flow in Venezuela, is probably a new EOR solution to reduce water cut and improve oil mobility in water flooded reservoirs, especially in heavy oil reservoirs exploited with water injection in Tuha Field. The mechanisms and recovery potential are unveiled with laboratory experiments and pilot tests.