Mechanistic research of a novel composite nano-oil-displacing agent to enhance low-permeability heavy oil reservoir recovery: taking the Ha-34 fault block as an example

To enhance the oil recovery of the Ha-34 fault block reservoir in the A'nan depression of the Erlian Basin (a low–permeability heavy oil reservoir), a novel composite nano-oil-displacing agent was formulated, several indoor experiments (stability, wettability, interfacial tension, emulsion state, oxygen-17 nuclear magnetic resonance, dynamic light scattering, zeta potential, and core flooding) were performed, and outdoor well group flooding projects were conducted. The following results were obtained: (1) visual observation (no precipitation) and a higher zeta potential (> | ±30 mV |) demonstrated exceptional stability of the nanofluid system; (2) the composite nano-oil-displacing agent (hereinafter referred to as the displacing agent) increased the contact angle of the oil droplets on the glutenite surface from 29.3° to 151.1°; (3) the displacing agent had a solid capacity to reduce the oil/water interfacial tension (0.065 mN/m, ultra lower) and could let the oil pass through the capillary throats; (4) the displacing agent increased the sweep efficiency of the reservoir and decreased the mobility ratio of the injection fluid to the formation fluid; (5) the SiO 2 nanoparticles dispersed in the fluid weakened the hydrogen bonds and formed small water clusters, which was the essence of oil displacement agents entering low porosity; (6) the displacing agent could detach the oil droplets from rock surfaces through structural disjoining pressure, which was the key to oil displacement agent peeled off the oil droplets; and (7) outdoor two-well and five-well group flooding projects increased oil production by 1269.55 tons (enhanced oil recovery 59.1%) and 3376.22 tons (enhanced oil recovery 53.3%), respectively. In other words, the displacing agent could peel off the oil droplets in the Ha-34 fault block reservoir by stronger oil‒rock (water) interactions, higher sweep coefficient, lower pore throat limit for oil displacement agents to enter, and greater structural disjoining pressure.