Revealing petroleum-water-CO2 emulsion stability by NMR about oil recovery and carbon storage

CO2 injection can simultaneously enhance oil recovery and carbon storage, but the stability of petroleum-water-CO2 emulsion affcet the production process and carbon storage. Emulsion characteristics is typically assessed via Nuclear Magnetic Resonance (NMR). It is essential to develop a theory to unlock the mechanisms of experimentation for harnessing the full potential of NMR in assessing emulsion stability and comprehending complex multiphase systems. The theory integrates experiments and a quasi-lattice wave physical model to understand the microscale mechanisms in NMR measurements of crude oil emulsion properties, and uncover the transfer-transition mode of H-1 quantum excited states, explaining T-2 relaxation. This forms a theoretical basis for numerical simulation of CPMG (Carr-Purcell-Meiboom-Gill) experiments by random walk algorithms and the boundary annihilation hypothesis. A strong link between NMR T-2 times and various character properties of Petroleum-Water-CO2 Emulsion samples is reflected, such as environmental scale, viscosity, CO2 adsorption, and molecular thermal motion. Additionally, parameter Theta was proposed to characterize emulsion stability, for penetrating the theory presented in this paper, and to provide a scientifically rigorous representation of crude oil emulsion stability. The experiments with CO2 treatment on crude oil emulsions were performed, demonstrating a highly effective theoretical correlation between interfacial tension in crude oil emulsions and CO(2 )pressure, with an exceptional fit to experimental data (R-2 > 0.99). When the pressure of CO2 treatment exceeds a critical threshold (approximately 17 MPa in this study), there is a substantial reduction in viscosity. Furthermore, a comparative assessment of samples before and after CO2 treatment using the parameter Theta demonstrated its reliability as an indicator of emulsion stability. It revealed a significant reduction of over 50% in the linear fit residual variance of Theta before and after subjecting the sample to 10 MPa carbon dioxide treatment, highlighting improved fluctuation stability. The slope of the Theta linear regression function signifies temporal stability. In a sample with 20% water content, the time evolution of the water phase decreases by 3.04%, while the oil phase experiences a substantial 57.77% reduction. Simultaneously, the midpoint of the range of the Theta linear regression function represents the environmental scale. The water phase environment scale increases by 8.72%, while the oil phase environment scale decreases by 8.74%, highlighting spatial evolution patterns.

Automated summary

This study develops a theory to unlock the potential of Nuclear Magnetic Resonance (NMR) in assessing emulsion stability and comprehending complex multiphase systems. The theory integrates experiments and a physical model to understand the microscale mechanisms in NMR measurements of crude oil emulsion properties. The results show a strong correlation between NMR T-2 times and various character properties of Petroleum-Water-CO2 Emulsion samples, and propose the parameter Theta to characterize emulsion stability.