Relaxivity-Insensitive Permeability Logging via Swanson Parameter Adjustment
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Solution Overview
Problem
Existing methods for converting NMR tool measurements into formation permeability logs are overly sensitive to relaxivity changes, which can be caused by changes in formation fluids, leading to inaccurate permeability measurements due to fluid invasion and wettability alterations.
Innovation Solution
The development of systems and methods that provide relaxivity-insensitive permeability logs by measuring spin-spin relaxation time distributions and processing them to determine a Swanson parameter, which is then adjusted to reduce dependence on relaxivity, using the Oraby parameter to convert the adjusted value into a permeability measurement, thereby minimizing the impact of fluid-type changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional NMR permeability measurement methods are used, then permeability logs can be obtained, but the measurements are overly sensitive to relaxivity changes caused by formation fluid variations
Solution Approach 1:
The patent transforms the T2 relaxation time distribution into a relaxivity-insensitive parameter space by applying a specific mathematical transformation. This changes the measurement parameter from T2 (which is relaxivity-dependent) to a new parameter that is invariant to relaxivity changes, thereby resolving the contradiction between measurement precision and reliability across different fluid conditions
Solution Approach 2:
The patent introduces an intermediary transformation step between the raw NMR measurement and the final permeability calculation. This intermediary parameter acts as a mediator that decouples the measurement from relaxivity variations, allowing accurate permeability determination regardless of formation fluid type or wettability conditions
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 results in significantly increased accuracy and consistency of permeability measurements across various rock types and fluid conditions, including water-wet, oil-wet, and wettability-altered formations, by isolating the intrinsic permeability from environmental and fluid-related influences.
Implementation Method 1
Nuclear magnetic resonance (NMR) logging tools are available for use in each of these environments. NMR tools operate by using an imposed static magnetic field, B0, to give nuclei with non-zero nuclear spin (non-zero angular momentum) split energy levels.
Implementation Method 2
The frequency of the pulse can be chosen to target specific nuclei (e.g., hydrogen). The polarized nuclei are perturbed simultaneously and, when the perturbation ends, they precess around the static magnetic field gradually re-polarizing to align with the static field once again while losing coherence in the transverse plane (T2 relaxation).
Data Source
AI summary
Systems and methods that provide relaxivity-insensitive permeability logs. At least some logging system embodiments include a logging tool assembly that measures spin-spin relaxation time distributions of formation fluid nuclei at different positions along a borehole. A processor operates on the measurements to provide a permeability log that is relatively insensitive to relaxivity coefficient changes and hence insensitive to changes in formation fluids. Thus, permeability logs will be relatively unaffected by invasion of the borehole fluids into the formation, even if surfactants in the borehole fluid cause large changes in formation wettability. For each position logged within a borehole, the processor may process the measured relaxation time distribution to determine a Swanson parameter value; adjust the Swanson parameter value to reduce dependence on relaxivity; and convert the adjusted value to a permeability measurement. Examples are included below to demonstrate the markedly increased permeability measurement accuracy.