The presence of paramagnetic species such as vanadyl complexes (VO2+) and free carbon radicals in petroleum disperse systems (PDSs) such as crude oil, bitumen, or kerogen causes significant interest of studying the structure of PDS, high-molecular weight components, and their effects on the physical and chemical properties of PDS products by magnetic resonance techniques. However, the lack of detailed studies keeps the exact structure, aggregation mechanism, and interaction with complex composites of the PDS still disputable. In this contribution, detailed electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) investigations, including advanced fast field cycling dynamic nuclear polarization, of heavy crude oil focused on vanadyl complexes are presented. A perceptible room-temperature 1H dynamic nuclear polarization (DNP) solid effect at the X-band (magnetic field of 300–400 mT corresponding to the EPR frequency of 9.5 GHz and NMR frequency of 14.6 MHz), with enhancement ±5, is observed at moderate microwave irradiation power in crude oil with a high concentration of VO2+, while no Overhauser DNP contribution is found. Using NMR T 2-encoding, DNP spectra and molecular dynamics, two components are distinguished, from which the one with slower dynamics exhibits higher DNP enhancement via VO2+ complexes. The observed difference is discussed in terms of electron–nuclear interaction and relative parts of hyperpolarized nuclear spins using an advanced model for DNP data simulation.

We present a detailed study of electron/nuclear interaction in a specific crude oil by continuous-wave and pulsed EPR, electron–nuclear double resonance (ENDOR) at W-band (94 GHz), and fast field-cycling dynamic nuclear polarization (FFC-DNP) at X-band. A perceptible non-Overhauser (solid) effect is found at room temperature as a result of the polarization transfer from the intrinsic oil “free” radicals to the 1H nuclei with different dynamics. On the basis of the analysis of the longitudinal nuclear relaxation times, three dynamical components described by different electron–proton coupling parameters were found, which in combination with ENDOR provides information about the distribution of the radicals in the high-molecular oil components.

Dynamic nuclear polarization (DNP) is one of the most useful methods to increase sensitivity in NMR spectroscopy. It is based on the transfer of magnetization from an electron to the nuclear spin system. Based on previous work that demonstrated the feasibility of integrating DNP with fast field cycling (FFC) relaxometry and the possibility to distinguish between different mechanisms, such as the Overhauser effect (OE) and the solid effect (SE), the first FFC study of the differential relaxation properties of a copolymer is presented. For this purpose, concentrated solutions of the polystyrene-block-polybutadiene-block-polystyrene (SBS) triblock copolymer and the corresponding homopolymers were investigated. T -T relaxation data are discussed in terms of molecular mobility and the presence of radicals. The DNP selective data indicate a dominant SE contribution to the enhancement of the NMR signal for both blocks of the triblock copolymer and for the homopolymer solutions. The enhancement factors are different for both polymer types and in the copolymer, which is explained by the individual H T relaxation times and different electron-nucleus coupling strength. The T relaxation dispersion measurements of the SE enhanced signal were performed, which led to improved signal-to-noise ratios that allowed the site-specific separation of relaxation times and their dependence on the Larmor frequency with a higher accuracy.

Molecular dynamics of the ionic liquid 1-ethyl-3-methylimidazolium bis­(trifluoromethyl sulfonyl)­imide (Emim-Tf2N) with either of the four organic stable radicals, TEMPO, 4-benzoyloxy-TEMPO, BDPA, and DPPH, is studied by using Nuclear Magnetic Resonance (NMR) and Dynamic Nuclear Polarization (DNP). In complex fluids at ambient temperature, NMR signal enhancement by DNP is frequently obtained by a combination of several mechanisms, where the Overhauser effect and solid effect are the most common. Understanding the interactions of free radicals with ionic liquid molecules is of particular significance due to their complex dynamics in these systems, influencing the properties of the ion-radical interaction. A combined analysis of EPR, DNP, and NMR relaxation dispersion is carried out for cations and anions containing, respectively, the NMR active nuclei 1H or 19F. Depending on the size and the chemical properties of the radical, different interaction processes are distinguished, namely, the Overhauser effect and solid effect, driven by dominating dipolar or scalar interactions. The resulting NMR relaxation dispersion is decomposed into rotational and translational contributions, allowing the identification of the corresponding correlation times of motion and interactions. The influence of electron relaxation time and electron–nuclear spin hyperfine coupling is discussed.

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The understanding of the dissolution and precipitation of minerals and its impact on the transport of fluids in porous media is essential for various subsurface applications, including shale gas production using hydraulic fracturing (“fracking”), CO2 sequestration, or geothermal energy extraction. In this work, we conducted a flow through column experiment to investigate the effect of barite precipitation following the dissolution of celestine and consequential permeability changes. These processes were assessed by a combination of 3D non-invasive magnetic resonance imaging, scanning electron microscopy, and conventional permeability measurements. The formation of barite overgrowths on the surface of celestine manifested in a reduced transverse relaxation time due to its higher magnetic susceptibility compared to the original celestine. Two empirical nuclear magnetic resonance (NMR) porosity–permeability relations could successfully predict the observed changes in permeability by the change in the transverse relaxation times and porosity. Based on the observation that the advancement of the reaction front follows the square root of time, and micro-continuum reactive transport modelling of the solid/fluid interface, it can be inferred that the mineral overgrowth is porous and allows the diffusion of solutes, thus affecting the mineral reactivity in the system. Our current investigation indicates that the porosity of the newly formed precipitate and consequently its diffusion properties depend on the supersaturation in solution that prevails during precipitation.

Three types of natural rocks�Bentheimer and Berea sandstones, as well as Liege Chalk�have been aged by immersion in a bitumen solution for extended periods of time in two steps, changing the surface conditions from water-wet to oilwet. NMR relaxation dispersion measurements were carried out on water and oil constituents, with saturated and aromatic molecules considered individually. In order to separate the different relaxation mechanisms discussed in the literature, 1 H and 19 F relaxation times were compared to 2 H for fully deuterated liquids: while 2 H relaxes predominantly by quadrupolar coupling, which is an intramolecular process, the remaining nuclei relax by dipolar coupling, which potentially consists of intra-and intermolecular contributions. The wettability change becomes evident in an increase of relaxation rates for oil and a corresponding decrease for water. However, this expected behavior dominates only for the spin−lattice relaxation rate R 1 at very low field strengths and for the spin−spin relaxation rate R 2 , while high-field longitudinal relaxation shows a much weaker or even reverse trend. This is attributed in part to a change of radical concentration on the pore surface upon coverage of the native rock surface by bitumen as well as by the change of surface chemistry and roughness. EPR and DNP measurements quantify the change of volume vs surface radical concentration in the rocks, and an improved understanding of the role of relaxation via paramagnetic centers is obtained. By means of comparing different fluids and nuclei in combination with a defined wettability change of natural rocks, a refined model for molecular dynamics in conjunction with NMR relaxation dispersion is proposed.

The use of vanadyl porphyrins either in synthetic compounds or naturally occurring in asphaltenes is investigated as a source of proton hyperpolarization via dynamic nuclear polarization (DNP) in nuclear magnetic resonance (NMR) experiments. The features of dynamics and location of the vanadyl VO2+ complex in aggregates within the oil asphaltene molecules are studied by means of DNP, electron paramagnetic resonance (EPR), and NMR field cycling relaxometry. Both the solid effect and Overhauser DNP were observed for the asphaltene solution in benzene, as well as in the solution and solid states for synthetic compounds. By comparison with a solution of synthetic vanadyl porphyrins, it is shown that vanadyl porphyrins in asphaltene aggregates are localized outside of the interface of the asphaltene aggregates and more exposed to the maltene molecules than “free” carbon-centered radicals associated with the core of asphaltene molecules. The perceptible contribution of scalar interaction is observed in solutions for both synthetic and asphaltene vanadyl porphyrins.