NMR T2 Cutoff Estimation Using Multifractal Analysis
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Solution Overview
Problem
Conventional methods inaccurately predict NMR T2 cutoff values for rock samples with complex pore structures, hindering the prediction of petrophysical properties essential for reservoir model building.
Innovation Solution
A nuclear magnetic resonance (NMR) logging method that uses multifractal dimension analysis and a temperature correction function to determine a temperature-corrected NMR T2 cutoff value, incorporating downhole temperature measurements and fractal parameters to accurately calibrate NMR responses for tight rock samples with varied mineral compositions and formation conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional prediction methods are used for NMR T2 cutoff values, then the process is simple, but the prediction accuracy is poor for rock samples with complex pore structures
Solution Approach 1:
The patent applies parameter changes by transforming the NMR T2 distribution parameters (mean, standard deviation, skewness, kurtosis) as functions of temperature. By establishing regression relationships between these parameters and temperature, the method accurately predicts T2 cutoff values at different temperatures, resolving the contradiction between prediction accuracy and method complexity.
Solution Approach 2:
The patent replaces conventional empirical prediction methods with a physics-based approach using NMR theory and statistical parameter analysis. By substituting the mechanical/empirical prediction system with a system based on NMR distribution parameter regression, the method achieves higher accuracy for complex pore structures while maintaining computational feasibility.
2Measurement precision
If temperature correction is not applied, then the measurement process is simpler, but the NMR T2 cutoff values are inaccurate for downhole conditions
Solution Approach 1:
The patent applies preliminary action by measuring the NMR T2 distribution parameters at multiple known temperatures during laboratory analysis before downhole application. This preliminary temperature-dependent characterization allows the development of regression models that can subsequently predict parameters at any downhole temperature, eliminating the need for actual downhole temperature measurements during the prediction process.
Solution Approach 2:
The patent creates a theoretical model (copy) of the temperature-dependent NMR T2 distribution behavior based on laboratory measurements. This model copies the essential temperature effects without requiring physical presence at downhole conditions, allowing accurate prediction of T2 cutoff values at reservoir temperatures through mathematical relationships rather than direct measurement.
3Loss of information
If multifractal dimension analysis is used, then the pore structure characterization is more detailed, but the parameter quality and resolution are reduced
Solution Approach 1:
The patent extracts the essential temperature-dependent parameters (mean, standard deviation, skewness, kurtosis) from the complete NMR T2 distribution without requiring full multifractal decomposition. By taking out only the critical statistical parameters that capture the dominant pore structure characteristics, the method maintains adequate characterization quality while avoiding the resolution degradation associated with complex multifractal analysis.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach generates a high-quality formation petrophysical property model for reserve assessment and production optimization by accurately predicting permeability and irreducible saturation, overcoming the limitations of low resolution and poor quality multifractal parameters in conventional methods.
Implementation Method 1
nuclear magnetic resonance (NMR) logging method includes obtaining an NMR well log
Implementation Method 2
determining an NMR distribution for each rock sample at multiple temperatures and determining a first parameter of the NMR distribution at each of a plurality of laboratory measured temperatures
Data Source
AI summary
A nuclear magnetic resonance (NMR) logging system and method is disclosed. The method may include obtaining an NMR well log, a measured downhole temperature, and at least one rock sample for a formation in a subsurface region. The method may further include determining an NMR distribution for each sample and selecting a set of samples based on the determined NMR distribution. For each selected sample, the method may further include determining a first parameter of the NMR distribution, a regression parameter of a relationship, and a first and second fractal parameters of the NMR distribution. The method may further include determining a second parameter of the NMR distribution based on the first and second fractal parameters, the regression parameter, and the downhole temperature. The method may still further include determining a parameter of the formation based on the second parameter of the NMR distributions of the set of samples.