Effects Evaluation on Multiround Injection of a N2 Foam & Viscosity Reducer to Improve the Recovery of Fault-Block Heavy Oil Reservoir with Edge-Bottom Water: A Two-Dimensional Visualization Experimental Study

The majority of edge-bottom water fault-block reservoirs in China have the problem of a low recovery factor during water flooding. Most of them suffer from serious water channeling, a rapid increase in water cut, and low sweeping efficiency. Measures need to be taken to further increase the recovery factor, among which nitrogen foam flooding and viscosity reducer flooding technologies are highly anticipated for this purpose. To fill this gap, this work targets reservoirs with edge-bottom water and fault blocks. First, on the basis of evaluating the effects of foaming agent and viscosity reducer, a 2D visual large flat physical model is designed to simulate the fault-block reservoirs with edge and bottom water. Then, after comparing the oil displacement effects of nitrogen foam and viscosity reducer systems using different injection methods, the flow characteristics and action patterns of foam and viscosity reducer are studied. The recovery factor of the hybrid injection scheme increased by 18.3% compared to the water flooding and was 4.2% higher than the slug injection. The water cutoff of the hybrid injection showed a linear decrease. Finally, the experiment clarifies the impact of injection rounds on nitrogen foam with viscosity reducer flooding and summarizes the mechanism of it through the changes in the oil saturation. The viscosity reducer significantly reduces the viscosity of crude oil and assists in foam plugging. Additionally, as the injection rounds increase, the effectiveness of profile control and water plugging decreases. In addition, most methods of profile control and water plugging are one-time injection; the experiment changes it to multiple rounds and introduces a conversion method of resistivity and oil saturation innovatively. The physical displacement experiment of big-scale size two-dimensional visualization model is carried out under simulated reservoir conditions, the influence of injection methods on recovery factor is studied, and the mechanism of enhancing oil recovery is clarified. Also, it is expected to address issues in edge-bottom water reservoirs with fault blocks, such as severe water channeling and limited displacement range.