Study on Foam Flooding Mechanism of Conglomerate Reservoir Based on Low Field Nuclear Magnetic Technology

Based on the combination of nuclear magnetic resonance technology and traditional foam displacement experiment, the morphology and utilization law of residual oil at pore level after foam flooding were explored and studied. The experimental results show that the QPJ-5 foam system with a gas-liquid ratio of 1: 1 and a concentration of 0.5% has a strong plugging effect in Xinjiang conglomerate reservoirs and fluid conditions, and its resistance coefficient reaches about 40. Compared with water flooding, foam flooding can increase oil recovery by 14.4 percentage points. The low-field nuclear magnetic resonance T2 spectrum analysis shows that after saturated oil, the crude oil can fill the large ( T2 > 100ms) and medium ( 10 < T2 < 100ms) pores of the entire core, in which the crude oil is mainly distributed in large pores, followed by medium pores. After a heavy water flooding, the peak area of large and medium pores in T2 spectrum decreased, and the peak area of large pores decreased most obviously, indicating that the heavy water without signal entered the core and displaced the crude oil with signal, so that the crude oil flowed out from the outlet section and the crude oil content in the core decreased. After analysis, heavy water flooding mainly used large pore crude oil. The peak point does not shift, indicating that heavy water in the injection process, along the dominant channel to displace crude oil, there is no obvious selection effect. After injection of 0.5 PV foaming agent and secondary heavy water flooding, the peak area of large and medium pores in T2 spectrum further decreased, and the peak area of medium pores decreased most obviously, indicating that foam flooding mainly used medium pore crude oil. At the same time, the peak point is offset, indicating that the foam agent has its unique profile control effect in the injection process, which increases the sweep effect, further uses the crude oil in the middle pore, makes the peak point shift to the left, and improves the recovery efficiency. It provides basic theory for foam flooding scheme design and effective development of conglomerate reservoirs in Xinjiang.