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LOW-FIELD NMR METHOD FOR ANALYSIS OF HEAVY OILS WITHOUT EXTRACTION OF ASPHALTENES

Nailia Khasanova, Boris Sakharov, Vladimir Volkov, Danis Nourgaliev

Abstract

For the analysis of heavy oil samples of the Ashalchinskoye deposit the combined nuclear magnetic resonance (NMR) method to measure the free-induction decay (FID) together with the Carr-Purcell-Meiboom-Gill (CPMG) echo signalпїЅs decay was used. The measurements were carried out on a NMR analyzer Chromatek-Proton 20M, operating at a frequency of 20 MHz. Special control program was created on the NMR analyzer, which automatically tunes and measures full FID curve, then switches to measuring the echo amplitudes decay by the CPMG pulse sequence, and the study is completed by co-processing together all experimental data. This technique makes it possible to measure the amplitudes of the NMR signals and the relaxation times T2 of the protons of heavy oil components in situ, including asphaltenes, without introducing any perturbations into the analyzed system. Under the influence of paramagnetic centers included to the composition of asphaltene, mainly vanadyl complexes on EPR data, the amplitude-relaxation characteristics of protons in the samples are divided into 6 groups related to solid asphaltenes (in crystalline and amorphous states), resins (high and low density), aromatic and saturated compounds. The amplitudes of NMR signals characterize the content of these fractions in the sample, and the relaxation times are determined by the mobility of molecules and the dynamics of their exchange between fractions. The proposed NMR method is promising for on-line monitoring the technological processes of heavy oil mining, transportation and processing under real conditions on temperature, pressure and the presence of dissolved gases, provided that the design of NMR sensor is adapted to industrial applications.

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DOI resolver: doi.org/10.5593/sgem2017h/15/s06.038

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