In the field of oil and gas extraction, reservoir modification is the core strategy for improving crude oil recovery efficiency. With the development of unconventional resources, nanofluid technology has attracted much attention due to its ability to significantly enhance reservoir permeability and crude oil fluidity. Nanofluids effectively improve rock wettability and reduce interfacial tension through their particle dispersibility and hydrophilicity, thereby enhancing the effectiveness of reservoir modification. However, how to accurately evaluate the performance of nanofluids has always been a challenge in the industry. Low field nuclear magnetic resonance (LF-NMR) technology, with its quantitative and non-destructive testing capabilities, has become a key tool for revealing the behavior of nanofluids and providing data support for optimizing reservoir improvement plans.

Application background of low field nuclear magnetic resonance technology

Traditional reservoir modification methods often rely on chemical flooding or hydraulic fracturing, but these technologies have problems of low efficiency and high cost. The introduction of nanofluids, through the unique properties of nanoparticles, can penetrate into the micropores of reservoirs and improve the efficiency of crude oil displacement. However, the dispersibility and hydrophilicity of nanoparticles directly affect their migration and interaction in reservoirs: poor dispersibility can lead to particle aggregation and blockage of pores, while insufficient hydrophilicity reduces their interaction with crude oil. Traditional detection methods such as microscopic observation, sedimentation testing, or spectroscopic analysis typically require sample pretreatment, which may damage fluid structures and cannot monitor dynamic processes in real-time. Low field nuclear magnetic resonance technology has emerged, which can perform in-situ analysis of nanofluids under non-destructive conditions, meeting the requirements for accuracy and real-time performance in reservoir modification research.

Brief Introduction to the Principle of Low Field Nuclear Magnetic Resonance

Low field nuclear magnetic resonance technology is based on the relaxation behavior of atomic nuclei in a magnetic field, particularly the response of hydrogen nuclei (such as hydrogen in water molecules). When the sample is placed in a low-intensity magnetic field, the hydrogen nucleus will release a signal and gradually relax back to equilibrium after being excited by radio frequency pulses. The T ₂ relaxation time (transverse relaxation time) reflects the degree of freedom of molecular motion: in nanofluids, the surface of particles binds water molecules, limiting their rotation and diffusion, thereby shortening the T ₂ time. By analyzing the T ₂ distribution spectrum, the specific surface area, dispersion state, and surface wetting characteristics of particles can be inverted, and the entire process does not require chemical labeling or physical invasion, maintaining the original properties of the sample.

Application of Low Field Nuclear Magnetic Resonance Technology in Nanofluid Research

Low field nuclear magnetic resonance technology provides multidimensional insights for the performance evaluation of nanofluids by measuring T ₂ relaxation time spectra.

Firstly, in terms of particle dispersibility evaluation, the T ₂ relaxation time directly reflects the state of the particles in the solvent: the shorter the T ₂ time, the larger the specific surface area and better dispersibility of the particles; On the contrary, prolonged T ₂ time implies particle aggregation and poor dispersion. This helps researchers optimize the formulation of nanofluids, ensuring uniform particle distribution and avoiding reservoir pore blockage. Secondly, in hydrophilicity analysis, the linear relationship between relaxation rate and particle surface area can be used to determine whether the particle surface is fully wetted by water molecules. Nanoparticles with strong hydrophilicity will adsorb more water molecules, restrict their movement, and shorten the overall relaxation time, thereby enhancing the wetting modification effect in the reservoir. In addition, this technology can also achieve real-time monitoring of dispersion stability: by continuously measuring the changes in T ₂ over time on the same sample, tracking the sedimentation and agglomeration process of nanoparticles, evaluating the long-term stability of fluid systems, and providing guarantees for persistent applications in reservoir modification.

Low field nuclear magnetic resonance technology is becoming a powerful tool in the study of nanofluid enhanced reservoir improvement effects. By accurately quantifying particle dispersibility, hydrophilicity, and stability, it not only deepens our understanding of the mechanism of nanofluid action, but also promotes innovation in reservoir modification technology. In the future, with the further popularization of this technology, combined with artificial intelligence data analysis, it is expected to achieve more intelligent oil and gas recovery strategies, injecting new impetus into the sustainable development of global energy. The synergistic application of nanofluids and low field nuclear magnetic resonance will undoubtedly lead the field of reservoir improvement towards a new era of higher accuracy and efficiency.