Methods for quantitative characterization of asphaltenes in solutions using two-dimensional low-field NMR measurement

A method for determining a concentration of asphaltenes in a solution, comprising:

• a. establishing a model for estimating the concentration of the asphaltenes in the solution, comprising the steps of:
• i. preparing a plurality of samples of solutions of the asphaltenes in a solvent wherein the solutions have varying concentrations of the asphaltenes and wherein concentrations of the asphaltenes are known for each sample within the plurality of samples;
• ii. exciting and detecting NMR signals from each sample within the plurality of samples using a two-dimensional NMR spectrometer;
• iii. measuring a diffusivity of an at least one response signal that is an NMR signal from the two-dimensional NMR spectrometer corresponding to each sample within the plurality of samples;
• iv. measuring a relaxation time of the at least one response signal that is the NMR signal from the two-dimensional NMR spectrometer corresponding to each sample within the plurality of samples;
• v. calculating a ratio of the diffusivity to the relaxation time for each sample within the plurality of samples;
• vi. fitting a linear equation to describe a relationship between the ratio of the diffusivity to the relaxation time and an asphaltene concentration by weight for each sample within the plurality of samples;
• and
• b. measuring the diffusivity and the relaxation time of the at least one response signal that is the NMR signal from the two-dimensional NMR spectrometer corresponding to a given solution sample for which the concentration of the asphaltenes is desired to be determined;
• c. calculating the ratio of the diffusivity to the relaxation time for the given solution sample;
• d. solving the linear equation as determined in step (a) (vi) using the ratio of the diffusivity to the relaxation time for the given solution sample as determined in step (c) to determine the asphaltene concentration in the given solution sample.