Research on nitrogen foam for enhancing oil recovery in harsh reservoirs

Owing to the simultaneous improvement of swept volume and oil displacement, foam flooding is one of the techniques that has been proven successfully in increasing EOR (Enhanced Oil Recovery). However, foam flooding in a harsh condition has not been fully addressed in the previous studies. The objective of this paper is to investigate the high-temperature and high-salinity resistant foam agents as a displacing chemical for improving the efficiency of oil recovery in harsh conditions. Firstly, the foam agents with excellent performances under harsh reservoir conditions were developed by screening and mixing. Then, the foam properties changing with temperature were studied under high pressure in the oil-free/oil-bearing environments. Finally, based on simulating reservoir formation conditions, a series of researches on the flooding characteristics of nitrogen foam were conducted. Results indicated that the optimum foam agents with low surface tension and high interfacial viscoelastic modulus performed excellently under high-temperature and high-salinity. Foam stability increased remarkably as pressure increased, and also largely affected by temperature. Higher concentration and pressure were in favor of foam properties in the presence of crude oil. In foam flooding experiments, the mobility reduction of foam was observed to be larger in the conditions of high pressure and low oil saturation, and nitrogen foam could significantly control the water cut and improve the oil recovery which were subject to the influencing factors (i.e., initial water cut, injected slug, foam quality, injected volume and foam stability).