Influence of Injection Parameters of Black Nanosheets on Enhancing Oil Recovery Performance in Low-Permeability Reservoirs

With the in-depth development of oil and gas resources, low-permeability reservoirs have gradually become a research hotspot for oilfield production increase targets. Increasing the stimulated reservoir volume (SRV) using fracturing is an important method for developing low-permeability reservoirs. However, the effect of water flooding development alone after fracturing remains limited. The black nanosheet (BN) oil displacement system, which has both profile control and oil displacement effects, is currently a popular method for developing unconventional reservoirs. It offers advantages such as a good imbibition oil displacement effect, stable chemical properties, and high sweep efficiency. However, there are few studies on its injection performance and oil displacement mechanism in low-permeability (10 × 10–3 μm2) and ultralow-permeability (1 × 10–3 μm2) reservoirs. In this study, the cationic-modified black nanosheet was taken as the research subject. Core displacement experiments and nuclear magnetic resonance analysis experiments designed through orthogonal design were used to study the influence mechanism of different injection parameters on the injection performance and oil displacement effect of the modified black nanosheet system. Results show that the black nanosheet significantly improved its injection performance compared with water flooding and enhanced the oil recovery degree. When the injection concentration was 0.002 wt %, the injection rate was 0.2 mL/min, the injected pore volume was 0.5 PV, and the core sample permeability was 1 × 10–3 μm2, the increase in oil recovery degree by black nanosheet after primary water flooding was the largest, reaching 14.13%OOIP (original oil in place). The nuclear magnetic resonance T2 spectrum further confirmed that under the above injection parameter conditions, black nanosheets could enter more tiny pores and displace more crude oil compared to water. More crude oil in large pores was displaced due to the reduction of phase boundary tension (i.e., capillary force). The research results of this paper provide a theoretical analysis basis for optimizing the injection parameters of the black nanosheet and improving its profile control and oil displacement effect in low-permeability reservoirs.