Analysis of the composition and properties of heavy oils in situ by Low Field NMR relaxation method

Abstract

For the analysis of heavy oils, the method of simultaneous measurement of the free induction decay (FID) together with the decay of the echo signal in the Carr-Purcell-Meiboom-Gill (CPMG) pulse program was used. The measurements were carried out on a «Chromatek-Proton 20M» NMR analyzer operating at a frequency of 20 MHz. A special control program was created on the NMR analyzer that automatically tunes and measures the full FID curve, then switches to measuring the decay of the echo amplitude by the CPMG pulse sequence, and then the investigation ends with a joint processing of all the experimental data. This method makes it possible to measure the amplitudes of NMR signals and the relaxation times T2 of protons of heavy oil components in situ, including asphaltenes, without any perturbations in the analyzed system. Under the influence of paramagnetic centers located in asphaltenes, the amplitude-relaxation characteristics of oil protons are divided into 7 groups associated with solid asphaltenes in crystalline and amorphous states, resins with high and low density, aromatic and saturated compounds. The NMR amplitudes of these fractions correlate well with the group composition of heavy oils as determined by gravitational-chromatographic SARA method. The combined FID + CPMG method can be recommended for determining the SARA composition and other properties of oil in situ. The behavior of fractions of heavy oil in the temperature range (-15оС ÷ +60оС) was investigated by SARA-NMR method. For the first time in situ, it has been shown that resins participate in the formation of asphaltenes in a closed volume when the oil is cooled from a stable state at room temperature, and vice versa, asphaltenes are disaggregated by heating with the release of resins. The SARA-NMR method is promising for the on-line monitoring of the production, transportation and processing of heavy oil in real conditions of temperature, pressure and dissolved gases. However, the design of the NMR sensor must be adapted to industrial applications. The possibilities of designing NMR probes on process pipelines of larger diameter than in laboratory instruments can be extended taking into account the procedure proposed for correcting the inhomogeneity of the magnetic field in the probed volume based on the FID signal of the liquid oil fraction.

Native Vanadyl Complexes in Crude Oil as Polarizing Agents for In Situ Proton Dynamic Nuclear Polarization

“…The integral intensity of component “B” with an average value of ⟨ T 2 ⟩ = 180 μs is 23 ± 2% and probably corresponds to the resin and asphaltene components (see Table ) in assumption of lower values of relaxation times because of aggregates and slower dynamics and 1 H spin density because of higher aromaticity in the corresponding fractions of oil; this interpretation is in agreement with typical values of relaxation times obtained for asphaltenes in solutions or crude oil. Hence, the residual unresolved peak “A” in the T 1 – T 2 map is expected to relate to the remaining fractions of oil, that is, the saturated and aromatic components.…”

“…It follows that the highest concentration of VO 2+ is in asphaltenes. As a result, Volkov et al 42 assumed that the relaxing effect of PCs of asphaltenes is transmitted through spin−spin systems of resins to protons of saturated and aromatic compounds. In our research, we do not exclude that VO 2+ complexes in resins also give a contribution to the obtained magnetic resonance results taking additionally into account the relatively large amount of resin components in oil (see Table 1).…”

“…In this contribution, crude oil from deposition of Ashalchinskoe was chosen because of the rather high vanadyl content and viscosity. Despite the fact that its composition is quite complex, it has been extensively studied by different analytical methods including various NMR and EPR techniques ,− and references therein. Mn-catalyzed oxidation of the Ashalchinskoe heavy oil in porous media was examined in ref by combining X-ray powder diffraction, thermal analysis, nonisothermal kinetic methods, and EPR approaches.…”

Probing the surface of synthetic opals with the vanadyl containing crude oil by using EPR and ENDOR techniques

“…We have chosen Ashalchinskoe oil (Volga-Ural basin, Republic Tatarstan, Russia) as one of the most complex petroleum systems but, from other side, as the most studied by different analytical methods including NMR, EPR, X-band ENDOR techniques (see [26][27][28][29][30][31][32] and references therein). Mn-catalyzed oxidation of the Ashalcha heavy oil in porous media was examined in ref.…”