Low-field NMR Method for Analysis of Heavy Oils without Extraction of Asphaltenes

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 signal's 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.