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

Abstract

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 1H quantum excited states, explaining T2 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 T2 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 Θ 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 CO2 pressure, with an exceptional fit to experimental data (R2 > 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 Θ demonstrated its reliability as an indicator of emulsion stability. It revealed a significant reduction of over 50% in the linear fit residual variance of Θ before and after subjecting the sample to 10 MPa carbon dioxide treatment, highlighting improved fluctuation stability. The slope of the Θ 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 Θ 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.