NMR Pore Size Distribution Analysis for Complex Carbonate Reservoirs
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Solution Overview
Problem
Current methods struggle to accurately determine the pore size distribution in sedimentary rock reservoirs, particularly for complex carbonate rocks, due to irregular microscopic pore volumes and reliance on assumptions in measurement methods.
Innovation Solution
A method involving drilling a core sample, determining porosity distribution, obtaining T2-distributions at different saturation levels, performing time domain subtraction, and analyzing NMR measurements to determine pore throat size distribution and surface relaxation, ultimately plotting pore throat sizes versus relaxation times to determine the pore size distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional measurement methods are used to determine pore size distribution, then the measurement process is simplified, but the accuracy and reliability of the results deteriorate due to reliance on assumptions and simplifications of irregular microscopic pore volumes
Solution Approach 1:
The patent replaces conventional mechanical measurement methods with Nuclear Magnetic Resonance (NMR) logging technology. The NMR method uses magnetic fields and radio waves to measure the transverse relaxation time (T2) of hydrogen protons in pore fluids, which correlates with pore size. This substitution eliminates the need for physical core analysis and provides accurate pore size distribution data for complex carbonate rocks without relying on simplifying assumptions.
Solution Approach 2:
The patent utilizes the relationship between NMR relaxation time parameters and pore size characteristics. By measuring the T2 distribution and applying appropriate scaling factors, the method transforms the NMR signal parameters into meaningful pore size distribution data. This parameter transformation allows accurate characterization of pore structures in carbonate rocks while maintaining measurement efficiency.
2Measurement precision
If X-ray microtomography is used to accurately describe irregular microscopic pore volumes, then the geometric description accuracy is improved, but the measurement complexity and time consumption increase significantly
Solution Approach 1:
The patent extracts the essential information needed for pore size distribution (hydrogen proton signals from pore fluids) using NMR logging, without requiring the complete and time-consuming 3D geometric reconstruction that X-ray microtomography provides. This extraction approach captures the critical pore size characteristics while avoiding the excessive time and computational resources required for full microtomographic analysis.
Solution Approach 2:
The patent creates a simplified but effective representation of pore size distribution through NMR T2 distributions, which serve as a proxy for the more complex X-ray microtomography data. This copying method provides sufficient accuracy for reservoir characterization and fluid flow modeling without requiring the time-intensive direct observation of complete pore geometries.
3Ease of operation
If conventional methods with assumptions are used to determine pore size distribution, then the ease of operation is improved, but the reliability of the pore size distribution data deteriorates for complex carbonate rocks
Solution Approach 1:
The patent replaces conventional measurement methods that rely on simplifying assumptions with NMR logging technology. The NMR method directly measures the magnetic properties of hydrogen protons in pore fluids, providing reliable pore size distribution data for complex carbonate rocks without requiring assumption-based interpretations. This substitution maintains operational ease while significantly improving data reliability.
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 provides a comprehensive and accurate method for determining pore size distribution, enhancing the understanding of fluid flow and capillary-pressure characteristics in reservoirs, which is crucial for oil recovery.
Implementation Method 1
obtain T2-distributions at different saturation levels of the core sample
Implementation Method 2
obtaining T2-distributions at different saturation levels of the core sample with formation brine, performing time domain subtraction on the T2-distributions
Implementation Method 3
obtaining T2-distributions at different saturation levels of the core sample with formation brine
Implementation Method 4
plotting the pore throat sizes as function of the relaxation times T2 to obtain the surface relaxation
Data Source
AI summary
A method for determining the pore size distribution in a reservoir, including the steps: drilling a core sample out of the reservoir, determining a porosity distribution along the core sample, obtaining T2-distributions at different saturation levels of the core sample with formation brine, performing time domain subtraction on the T2-distributions to obtain T2-distributions at all saturation levels, determining the pore throat size distribution along the core sample, determining first porosities from the T2-distributions that correspond to second porosities of the pore throat size distribution for each saturation level, determining T2-distributions at the first porosities from the T2-distributions, determining pore throat sizes at the second porosities from the pore throat size distributions, plotting the pore throat sizes as function of the relaxation times T2 to obtain the surface relaxation, and determining the pore size distribution of the reservoir.