Open AccessAnalysis of the composition and properties of heavy oils in situ by Low Field NMR relaxation method
Author(s) -
Vladimir Ya. Volkov,
Boris V. Sakharov,
N. M. Khasanova,
Д. К. Нургалиев
Publication year - 2018
Publication title -
georesursy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.291
H-Index - 5
eISSN - 1608-5078
pISSN - 1608-5043
DOI - 10.18599/grs.2018.4.308-323
Subject(s) - asphaltene , chemistry , analytical chemistry (journal) , relaxation (psychology) , amplitude , pulse sequence , in situ , nuclear magnetic resonance , chromatography , organic chemistry , physics , psychology , social psychology , quantum mechanics
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.