NMR Pore Distribution Analysis via Delta T2 Signal Differences
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Solution Overview
Problem
Current NMR technologies face challenges in accurately resolving and interpreting pore size distributions from T2 distributions due to regularization and smoothing processes, which limits the resolution and ability to distinguish variations in NMR responses during changes in saturation or fluid composition in rock formations.
Innovation Solution
The method involves calculating differences between NMR decays at different conditions (ΔT2 distributions) using Laplace inversion to produce a distribution that highlights changes in porosity and fluid composition, allowing for better identification of pore size variations and fluid changes, such as during water flooding or invasion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If regularization and smoothing processes are applied to NMR T2 distributions, then the data becomes more stable and easier to interpret, but the resolution of pore size distribution analysis deteriorates
Solution Approach 1:
The patent segments the NMR decay signal into multiple exponential components, each representing different pore size ranges. By fitting the decay to a sum of exponentials with distinct T2 values, the method resolves pore size distributions without applying smoothing that would blur these distinctions. The segmentation allows simultaneous achievement of stability through mathematical modeling and resolution through distinct component identification.
Solution Approach 2:
The patent transforms the one-dimensional T2 distribution problem into a multi-dimensional analysis by considering multiple decay components with different amplitudes and time constants. This dimensional expansion allows the system to resolve fine pore size variations while maintaining stability through the constrained multi-parameter fitting approach, avoiding the need for smoothing operations.
2Adaptability or versatility
If traditional NMR methods are used to measure porosity, then the measurement is independent of lithology, but the ability to distinguish fluid composition changes and pore size variations deteriorates
Solution Approach 1:
The patent applies local quality by analyzing different segments of the T2 distribution curve with different interpretation criteria. Short T2 components are interpreted as small pores or bound fluid, while long T2 components represent large pores or free fluid. This localized analysis within different parts of the distribution enables simultaneous lithology-independent porosity measurement and detailed fluid composition discrimination.
Solution Approach 2:
The patent changes the interpretation parameters of the NMR data by fitting multiple exponential components with varying T2 values and amplitudes. By analyzing the distribution of these parameters across the decay curve, the method extracts both total porosity (lithology-independent) and detailed pore size/fluid composition information, resolving the contradiction between versatility and precision.
3Loss of information
If multiple NMR measurements are taken at different conditions, then more information about fluid changes is obtained, but the complexity of data processing increases
Solution Approach 1:
The patent performs preliminary exponential fitting on each individual NMR decay curve before comparing them. By pre-processing each measurement to extract T2 components and their amplitudes, the system simplifies subsequent comparisons between different conditions. This preliminary action reduces the complexity of analyzing multiple measurements while preserving all information about fluid changes.
Solution Approach 2:
The patent uses the exponential decay parameters (T2 values and amplitudes) as intermediary variables between the raw NMR signals and the final interpretation of fluid changes. These intermediaries provide a standardized framework for comparing measurements at different conditions, reducing processing complexity while maintaining full information about fluid composition and pore size variations.
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 enhances the resolution of pore size distribution analysis and fluid changes, providing more accurate information on porosity and fluid composition, aiding in oil and gas production strategies and reservoir characterization.
Implementation Method 1
NMR tools typically have a DC magnet that produces a static magnetic field at a desired test location
Implementation Method 2
The radio frequency magnetic field produces a torque on the magnetization vector that causes it to rotate about the axis of the applied radio frequency field
Implementation Method 3
Nuclear Magnetic Resonance (NMR) tools used for well-logging or downhole fluid characterization measure the response of nuclear spins in formation fluids to applied magnetic fields
Data Source
AI summary
For a given medium, a property may be inferred based on nuclear magnetic resonance (NMR) data. NMR data that includes two or more different NMR signals are used. Differences between any particular two of the two or more different NMR decays are computed and a distribution is produced based on the computed differences. The property of the medium may be inferred using the produced distribution. The produced distribution features the change in a parameter. The NMR distributions may be T2 distributions, T1 distributions, diffusion, or any other type of NMR data. The NMR data may be acquired: at different times, for different levels of invasion, before and after water flooding, or for different saturation states. The inferred property may pertain to the oil and gas industry, material analysis, medicine, pharmaceuticals, the process industry, or the food industry. For example, the inferred property may be the porosity of a subsurface formation.