Two-Dimensional NMR Asphaltene Quantification via Diffusivity Relaxation Ratio
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Solution Overview
Problem
Current methods for in-situ measuring asphaltene content in hydrocarbon reservoirs are limited in accuracy, particularly in heavy oil reservoirs, as one-dimensional NMR measurements struggle with overlapping signals, and existing methods like downhole fluid analysis are not effective in determining concentration distributions.
Innovation Solution
A two-dimensional low-field NMR method is developed to estimate asphaltene concentration by measuring diffusivity and relaxation time in multiple samples, creating a linear model that correlates the ratio of diffusivity to relaxation time with asphaltene concentration, allowing for precise determination of asphaltene content in solutions using a system with an NMR probe and computer processor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If one-dimensional NMR measurement is used to measure asphaltene concentration, then the measurement process is simple, but the measurement precision is poor due to signal overlapping
Solution Approach 1:
The patent transitions from one-dimensional NMR measurement to two-dimensional NMR measurement by adding the diffusivity dimension to the traditional T2 relaxation time dimension. This dimensional expansion separates overlapping signals from different fluid components (asphaltenes, resins, aromatics, paraffins) in the T2-D joint spectrum, enabling precise identification and quantification of asphaltene concentration that was not possible with 1D NMR alone.
2Loss of information
If downhole fluid analysis with optical filters is used to measure asphaltene content, then the compositional analysis is provided, but the concentration distribution determination is limited
Solution Approach 1:
The patent changes the measurement parameters from optical properties (color identification via optical filters) to physical properties (diffusivity and relaxation time). By measuring the T2 relaxation time and diffusivity coefficients of different fluid components and comparing them to reference values, the system can accurately determine asphaltene concentration distribution, overcoming the limitations of optical methods in providing quantitative concentration data.
3Measurement precision
If two-dimensional NMR measurement is used to determine asphaltene concentration, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The patent performs preliminary measurements of T2 relaxation time and diffusivity coefficients for multiple fluid components (asphaltenes, resins, aromatics, paraffins) under controlled conditions before actual field application. These reference values are stored and used to interpret field measurements, simplifying the complex inversion process and enabling accurate asphaltene concentration determination without requiring complex real-time analysis systems.
Data Source
AI summary
A method for determining the concentration of asphaltenes in a solution is described. A model is first established for estimating the concentration of asphaltenes in a solution based on multiple samples of solutions of asphaltenes in the solvent in which the concentrations are known. The multiple samples have varying concentrations of asphaltenes. The diffusivity and relaxation time are measured for each sample using two-dimensional NMR. The ratio of diffusivity to relaxation time for each sample is then calculated. A linear equation is determined to fit the relationship between the ratio of diffusivity to relaxation time and the asphaltene concentration by weight for the multiple samples, thus creating the model. For a given solution sample for which the concentration of asphaltenes is desired to be determined, diffusivity and relaxation time are determined using two-dimensional NMR, and the ratio of diffusivity to relaxation time is calculated. This ratio is then used with the model, so that the linear equation can be solved for the asphaltene concentration in the given solution sample.